fix(tui): use neutral Mermaid colors

Co-authored-by: Dax Raad <826656+thdxr@users.noreply.github.com>
Co-authored-by: Aiden Cline <rekram1-node@users.noreply.github.com>

bun.lock

@@ -395,6 +395,7 @@
         "ignore": "7.0.5",
         "immer": "11.1.4",
         "jsonc-parser": "3.3.1",
+        "mime-types": "3.0.2",
         "tree-sitter-bash": "0.25.0",
         "tree-sitter-powershell": "0.25.10",
         "turndown": "7.2.0",
@@ -570,6 +571,20 @@
         "@typescript/native-preview": "catalog:",
       },
     },
+    "packages/merman": {
+      "name": "@opencode-ai/merman",
+      "version": "0.0.0",
+      "dependencies": {
+        "@opencode-ai/plugin": "workspace:*",
+        "@opentui/core": "catalog:",
+        "string-width": "catalog:",
+      },
+      "devDependencies": {
+        "@tsconfig/bun": "catalog:",
+        "@types/bun": "catalog:",
+        "@typescript/native-preview": "catalog:",
+      },
+    },
     "packages/plugin": {
       "name": "@opencode-ai/plugin",
       "version": "1.18.8",
@@ -880,6 +895,7 @@
       "dependencies": {
         "@opencode-ai/client": "workspace:*",
         "@opencode-ai/core": "workspace:*",
+        "@opencode-ai/merman": "workspace:*",
         "@opencode-ai/plugin": "workspace:*",
         "@opencode-ai/schema": "workspace:*",
         "@opencode-ai/simulation": "workspace:*",
@@ -2063,6 +2079,8 @@
 
     "@opencode-ai/httpapi-codegen": ["@opencode-ai/httpapi-codegen@workspace:packages/httpapi-codegen"],
 
+    "@opencode-ai/merman": ["@opencode-ai/merman@workspace:packages/merman"],
+
     "@opencode-ai/plugin": ["@opencode-ai/plugin@workspace:packages/plugin"],
 
     "@opencode-ai/protocol": ["@opencode-ai/protocol@workspace:packages/protocol"],

packages/app/e2e/performance/timeline-stability/scroll-interaction.spec.ts

@@ -134,22 +134,6 @@ test("does not pull a keyboard-scrolled user during shell remeasurement", async
   await reportVisualStability(testInfo, "keyboard-during-resize", trace, anchorPlan(regions))
 })
 
-test("accumulates rapid page key presses", async ({ page }) => {
-  await setupTimeline(page, {
-    messages: history(80),
-    viewport: { width: 1400, height: 700 },
-  })
-  const scroller = page.locator(".scroll-view__viewport", { has: page.locator("[data-timeline-row]") })
-  await scroller.evaluate((element) => (element.scrollTop = element.scrollHeight))
-  await scroller.focus()
-  const before = await scroller.evaluate((element) => ({ top: element.scrollTop, height: element.clientHeight }))
-
-  for (let index = 0; index < 3; index++) await scroller.press("PageUp")
-
-  await page.waitForTimeout(150)
-  expect(before.top - (await scroller.evaluate((element) => element.scrollTop))).toBeGreaterThan(before.height * 2.2)
-})
-
 test("tracks keyboard scrolling from a focused timeline descendant", async ({ page }, testInfo) => {
   const shellID = "prt_descendant_keyboard_01_shell"
   const timeline = await setupTimeline(page, {

packages/app/src/context/server-session-v2-reducer.test.ts

@@ -153,4 +153,88 @@ describe("v2 session reducer", () => {
 
     expect(result).toMatchObject({ sessionID: "ses_1", missing: "msg_user", touched: [] })
   })
+
+  test("removes cancelled input from the pending promotion fold", () => {
+    const reducer = createV2SessionReducer()
+    reducer.reduce(
+      [],
+      event({
+        ...base,
+        id: "evt_admitted",
+        type: "session.input.admitted",
+        data: {
+          sessionID: "ses_1",
+          inputID: "msg_user",
+          input: { type: "user", delivery: "queue", data: { text: "cancel me" } },
+        },
+      }),
+    )
+    reducer.reduce(
+      [],
+      event({
+        ...base,
+        id: "evt_cancelled",
+        type: "session.input.cancelled",
+        data: { sessionID: "ses_1", inputID: "msg_user" },
+      }),
+    )
+    const result = reducer.reduce(
+      [],
+      event({
+        ...base,
+        id: "evt_promoted",
+        type: "session.input.promoted",
+        data: { sessionID: "ses_1", inputID: "msg_user" },
+      }),
+    )
+
+    expect(result).toMatchObject({ missing: "msg_user" })
+  })
+
+  test("keeps steered input available to the promotion fold", () => {
+    const reducer = createV2SessionReducer()
+    reducer.reduce(
+      [],
+      event({
+        ...base,
+        id: "evt_admitted",
+        type: "session.input.admitted",
+        data: {
+          sessionID: "ses_1",
+          inputID: "msg_user",
+          input: { type: "user", delivery: "queue", data: { text: "steer me" } },
+        },
+      }),
+    )
+    reducer.reduce(
+      [],
+      event({
+        ...base,
+        id: "evt_steered",
+        type: "session.input.steered",
+        data: { sessionID: "ses_1", inputID: "msg_user" },
+      }),
+    )
+    reducer.reduce(
+      [],
+      event({
+        ...base,
+        id: "evt_queued",
+        type: "session.input.queued",
+        data: { sessionID: "ses_1", inputID: "msg_user" },
+      }),
+    )
+
+    const result = reducer.reduce(
+      [],
+      event({
+        ...base,
+        id: "evt_promoted",
+        type: "session.input.promoted",
+        data: { sessionID: "ses_1", inputID: "msg_user" },
+      }),
+    )
+
+    expect(result?.messages).toMatchObject([{ id: "msg_user", type: "user", text: "steer me" }])
+  })
 })

packages/app/src/context/server-session-v2-reducer.ts

@@ -29,6 +29,9 @@ export function createV2SessionReducer() {
       case "session.input.admitted":
         pending.set(key(sessionID, event.data.inputID), event.data.input)
         return result([...source])
+      case "session.input.cancelled":
+        pending.delete(key(sessionID, event.data.inputID))
+        return
       case "session.input.promoted": {
         const input = pending.get(key(sessionID, event.data.inputID))
         pending.delete(key(sessionID, event.data.inputID))

packages/app/src/pages/session.tsx

@@ -688,6 +688,8 @@ export default function Page() {
     return {
       queryKey: [...vcsKey(), mode] as const,
       enabled,
+      refetchOnMount: "always" as const,
+      refetchOnWindowFocus: true,
       queryFn: mode
         ? () =>
             sdk()
@@ -701,6 +703,16 @@ export default function Page() {
     }
   })
   const refreshVcs = debounce(() => void queryClient.invalidateQueries({ queryKey: vcsKey() }), 100)
+  createEffect(
+    on(
+      () => desktopReviewOpen() || mobileChanges(),
+      (open, previous) => {
+        if (!open || previous || !desktopFileTreeOpen() || vcsQuery.isFetching) return
+        refreshVcs()
+      },
+      { defer: true },
+    ),
+  )
   const reviewDiffs = () => {
     if (reviewMode() === "git" || reviewMode() === "branch")
       // avoids suspense
@@ -947,19 +959,6 @@ export default function Page() {
     ),
   )
 
-  const stopVcs = sdk().event.listen((evt) => {
-    const details = evt.details as { type: string; properties?: unknown }
-    if (details.type !== "file.watcher.updated" && details.type !== "filesystem.changed") return
-    const props =
-      typeof details.properties === "object" && details.properties
-        ? (details.properties as Record<string, unknown>)
-        : undefined
-    const file = typeof props?.file === "string" ? props.file : undefined
-    if (!file || file.startsWith(".git/")) return
-    refreshVcs()
-  })
-  onCleanup(stopVcs)
-
   createEffect(
     on(
       () => sdk().directory,

packages/client/src/effect/api/api.ts

@@ -263,38 +263,52 @@ export type Endpoint5_23Input = { readonly sessionID: Session.ID }
 export type Endpoint5_23Output = ReadonlyArray<SessionPending.Info>
 export type SessionPendingListOperation<E = never> = (input: Endpoint5_23Input) => Effect.Effect<Endpoint5_23Output, E>
 
-export type Endpoint5_24Input = { readonly sessionID: Session.ID }
-export type Endpoint5_24Output = ReadonlyArray<InstructionEntry.Info>
-export type SessionInstructionsEntryListOperation<E = never> = (
+export type Endpoint5_24Input = { readonly sessionID: Session.ID; readonly inputID: SessionMessage.ID }
+export type Endpoint5_24Output = void
+export type SessionPendingCancelOperation<E = never> = (
   input: Endpoint5_24Input,
 ) => Effect.Effect<Endpoint5_24Output, E>
 
-export type Endpoint5_25Input = {
+export type Endpoint5_25Input = { readonly sessionID: Session.ID; readonly inputID: SessionMessage.ID }
+export type Endpoint5_25Output = void
+export type SessionPendingSteerOperation<E = never> = (input: Endpoint5_25Input) => Effect.Effect<Endpoint5_25Output, E>
+
+export type Endpoint5_26Input = { readonly sessionID: Session.ID; readonly inputID: SessionMessage.ID }
+export type Endpoint5_26Output = void
+export type SessionPendingQueueOperation<E = never> = (input: Endpoint5_26Input) => Effect.Effect<Endpoint5_26Output, E>
+
+export type Endpoint5_27Input = { readonly sessionID: Session.ID }
+export type Endpoint5_27Output = ReadonlyArray<InstructionEntry.Info>
+export type SessionInstructionsEntryListOperation<E = never> = (
+  input: Endpoint5_27Input,
+) => Effect.Effect<Endpoint5_27Output, E>
+
+export type Endpoint5_28Input = {
   readonly sessionID: Session.ID
   readonly key: InstructionEntry.Key
   readonly value: Schema.Json
 }
-export type Endpoint5_25Output = void
+export type Endpoint5_28Output = void
 export type SessionInstructionsEntryPutOperation<E = never> = (
-  input: Endpoint5_25Input,
-) => Effect.Effect<Endpoint5_25Output, E>
+  input: Endpoint5_28Input,
+) => Effect.Effect<Endpoint5_28Output, E>
 
-export type Endpoint5_26Input = { readonly sessionID: Session.ID; readonly key: InstructionEntry.Key }
-export type Endpoint5_26Output = void
+export type Endpoint5_29Input = { readonly sessionID: Session.ID; readonly key: InstructionEntry.Key }
+export type Endpoint5_29Output = void
 export type SessionInstructionsEntryRemoveOperation<E = never> = (
-  input: Endpoint5_26Input,
-) => Effect.Effect<Endpoint5_26Output, E>
+  input: Endpoint5_29Input,
+) => Effect.Effect<Endpoint5_29Output, E>
 
-export type Endpoint5_27Input = { readonly sessionID: Session.ID; readonly prompt: string }
-export type Endpoint5_27Output = { readonly text: string }
-export type SessionGenerateOperation<E = never> = (input: Endpoint5_27Input) => Effect.Effect<Endpoint5_27Output, E>
+export type Endpoint5_30Input = { readonly sessionID: Session.ID; readonly prompt: string }
+export type Endpoint5_30Output = { readonly text: string }
+export type SessionGenerateOperation<E = never> = (input: Endpoint5_30Input) => Effect.Effect<Endpoint5_30Output, E>
 
-export type Endpoint5_28Input = {
+export type Endpoint5_31Input = {
   readonly sessionID: Session.ID
   readonly after?: Event.Seq | undefined
   readonly follow?: boolean | undefined
 }
-export type Endpoint5_28Output =
+export type Endpoint5_31Output =
   | (
       | {
           readonly id: Event.ID
@@ -404,6 +418,33 @@ export type Endpoint5_28Output =
             readonly input: SessionPending.Message
           }
         }
+      | {
+          readonly id: Event.ID
+          readonly created: DateTime.Utc
+          readonly metadata?: { readonly [x: string]: unknown } | undefined
+          readonly type: "session.input.cancelled"
+          readonly durable: { readonly aggregateID: string; readonly seq: Event.Seq; readonly version: Event.Version }
+          readonly location?: Location.Ref | undefined
+          readonly data: { readonly sessionID: Session.ID; readonly inputID: SessionMessage.ID }
+        }
+      | {
+          readonly id: Event.ID
+          readonly created: DateTime.Utc
+          readonly metadata?: { readonly [x: string]: unknown } | undefined
+          readonly type: "session.input.steered"
+          readonly durable: { readonly aggregateID: string; readonly seq: Event.Seq; readonly version: Event.Version }
+          readonly location?: Location.Ref | undefined
+          readonly data: { readonly sessionID: Session.ID; readonly inputID: SessionMessage.ID }
+        }
+      | {
+          readonly id: Event.ID
+          readonly created: DateTime.Utc
+          readonly metadata?: { readonly [x: string]: unknown } | undefined
+          readonly type: "session.input.queued"
+          readonly durable: { readonly aggregateID: string; readonly seq: Event.Seq; readonly version: Event.Version }
+          readonly location?: Location.Ref | undefined
+          readonly data: { readonly sessionID: Session.ID; readonly inputID: SessionMessage.ID }
+        }
       | {
           readonly id: Event.ID
           readonly created: DateTime.Utc
@@ -862,19 +903,19 @@ export type Endpoint5_28Output =
         }
     )
   | EventLog.Synced
-export type SessionLogOperation<E = never> = (input: Endpoint5_28Input) => Stream.Stream<Endpoint5_28Output, E>
+export type SessionLogOperation<E = never> = (input: Endpoint5_31Input) => Stream.Stream<Endpoint5_31Output, E>
 
-export type Endpoint5_29Input = { readonly sessionID: Session.ID }
-export type Endpoint5_29Output = void
-export type SessionInterruptOperation<E = never> = (input: Endpoint5_29Input) => Effect.Effect<Endpoint5_29Output, E>
+export type Endpoint5_32Input = { readonly sessionID: Session.ID }
+export type Endpoint5_32Output = void
+export type SessionInterruptOperation<E = never> = (input: Endpoint5_32Input) => Effect.Effect<Endpoint5_32Output, E>
 
-export type Endpoint5_30Input = { readonly sessionID: Session.ID }
-export type Endpoint5_30Output = void
-export type SessionBackgroundOperation<E = never> = (input: Endpoint5_30Input) => Effect.Effect<Endpoint5_30Output, E>
+export type Endpoint5_33Input = { readonly sessionID: Session.ID }
+export type Endpoint5_33Output = void
+export type SessionBackgroundOperation<E = never> = (input: Endpoint5_33Input) => Effect.Effect<Endpoint5_33Output, E>
 
-export type Endpoint5_31Input = { readonly sessionID: Session.ID; readonly messageID: SessionMessage.ID }
-export type Endpoint5_31Output = SessionMessage.Info
-export type SessionMessageOperation<E = never> = (input: Endpoint5_31Input) => Effect.Effect<Endpoint5_31Output, E>
+export type Endpoint5_34Input = { readonly sessionID: Session.ID; readonly messageID: SessionMessage.ID }
+export type Endpoint5_34Output = SessionMessage.Info
+export type SessionMessageOperation<E = never> = (input: Endpoint5_34Input) => Effect.Effect<Endpoint5_34Output, E>
 
 export interface SessionApi<E = never> {
   readonly list: SessionListOperation<E>
@@ -902,7 +943,12 @@ export interface SessionApi<E = never> {
     readonly commit: SessionRevertCommitOperation<E>
   }
   readonly context: SessionContextOperation<E>
-  readonly pending: { readonly list: SessionPendingListOperation<E> }
+  readonly pending: {
+    readonly list: SessionPendingListOperation<E>
+    readonly cancel: SessionPendingCancelOperation<E>
+    readonly steer: SessionPendingSteerOperation<E>
+    readonly queue: SessionPendingQueueOperation<E>
+  }
   readonly instructions: {
     readonly entry: {
       readonly list: SessionInstructionsEntryListOperation<E>

packages/client/src/effect/generated/client.ts

@@ -80,6 +80,12 @@ import type {
   Endpoint5_30Output,
   Endpoint5_31Input,
   Endpoint5_31Output,
+  Endpoint5_32Input,
+  Endpoint5_32Output,
+  Endpoint5_33Input,
+  Endpoint5_33Output,
+  Endpoint5_34Input,
+  Endpoint5_34Output,
   Endpoint6_0Input,
   Endpoint6_0Output,
   Endpoint7_0Input,
@@ -523,37 +529,58 @@ const Endpoint5_23 = (raw: RawClient["server.session"]) => (input: Endpoint5_23I
 
 const Endpoint5_24 = (raw: RawClient["server.session"]) => (input: Endpoint5_24Input) =>
   preserveEffect<Endpoint5_24Output>()(
-    raw["session.instructions.entry.list"]({ params: { sessionID: input["sessionID"] } }).pipe(
+    raw["session.pending.cancel"]({ params: { sessionID: input["sessionID"], inputID: input["inputID"] } }).pipe(
       Effect.mapError(mapClientError),
-      Effect.map((value) => value.data),
     ),
   )
 
 const Endpoint5_25 = (raw: RawClient["server.session"]) => (input: Endpoint5_25Input) =>
   preserveEffect<Endpoint5_25Output>()(
-    raw["session.instructions.entry.put"]({
-      params: { sessionID: input["sessionID"], key: input["key"] },
-      payload: { value: input["value"] },
-    }).pipe(Effect.mapError(mapClientError)),
+    raw["session.pending.steer"]({ params: { sessionID: input["sessionID"], inputID: input["inputID"] } }).pipe(
+      Effect.mapError(mapClientError),
+    ),
   )
 
 const Endpoint5_26 = (raw: RawClient["server.session"]) => (input: Endpoint5_26Input) =>
   preserveEffect<Endpoint5_26Output>()(
-    raw["session.instructions.entry.remove"]({ params: { sessionID: input["sessionID"], key: input["key"] } }).pipe(
+    raw["session.pending.queue"]({ params: { sessionID: input["sessionID"], inputID: input["inputID"] } }).pipe(
       Effect.mapError(mapClientError),
     ),
   )
 
 const Endpoint5_27 = (raw: RawClient["server.session"]) => (input: Endpoint5_27Input) =>
   preserveEffect<Endpoint5_27Output>()(
-    raw["session.generate"]({ params: { sessionID: input["sessionID"] }, payload: { prompt: input["prompt"] } }).pipe(
+    raw["session.instructions.entry.list"]({ params: { sessionID: input["sessionID"] } }).pipe(
       Effect.mapError(mapClientError),
       Effect.map((value) => value.data),
     ),
   )
 
 const Endpoint5_28 = (raw: RawClient["server.session"]) => (input: Endpoint5_28Input) =>
-  preserveStream<Endpoint5_28Output>()(
+  preserveEffect<Endpoint5_28Output>()(
+    raw["session.instructions.entry.put"]({
+      params: { sessionID: input["sessionID"], key: input["key"] },
+      payload: { value: input["value"] },
+    }).pipe(Effect.mapError(mapClientError)),
+  )
+
+const Endpoint5_29 = (raw: RawClient["server.session"]) => (input: Endpoint5_29Input) =>
+  preserveEffect<Endpoint5_29Output>()(
+    raw["session.instructions.entry.remove"]({ params: { sessionID: input["sessionID"], key: input["key"] } }).pipe(
+      Effect.mapError(mapClientError),
+    ),
+  )
+
+const Endpoint5_30 = (raw: RawClient["server.session"]) => (input: Endpoint5_30Input) =>
+  preserveEffect<Endpoint5_30Output>()(
+    raw["session.generate"]({ params: { sessionID: input["sessionID"] }, payload: { prompt: input["prompt"] } }).pipe(
+      Effect.mapError(mapClientError),
+      Effect.map((value) => value.data),
+    ),
+  )
+
+const Endpoint5_31 = (raw: RawClient["server.session"]) => (input: Endpoint5_31Input) =>
+  preserveStream<Endpoint5_31Output>()(
     Stream.unwrap(
       raw["session.log"]({
         params: { sessionID: input["sessionID"] },
@@ -565,18 +592,18 @@ const Endpoint5_28 = (raw: RawClient["server.session"]) => (input: Endpoint5_28I
     ),
   )
 
-const Endpoint5_29 = (raw: RawClient["server.session"]) => (input: Endpoint5_29Input) =>
-  preserveEffect<Endpoint5_29Output>()(
+const Endpoint5_32 = (raw: RawClient["server.session"]) => (input: Endpoint5_32Input) =>
+  preserveEffect<Endpoint5_32Output>()(
     raw["session.interrupt"]({ params: { sessionID: input["sessionID"] } }).pipe(Effect.mapError(mapClientError)),
   )
 
-const Endpoint5_30 = (raw: RawClient["server.session"]) => (input: Endpoint5_30Input) =>
-  preserveEffect<Endpoint5_30Output>()(
+const Endpoint5_33 = (raw: RawClient["server.session"]) => (input: Endpoint5_33Input) =>
+  preserveEffect<Endpoint5_33Output>()(
     raw["session.background"]({ params: { sessionID: input["sessionID"] } }).pipe(Effect.mapError(mapClientError)),
   )
 
-const Endpoint5_31 = (raw: RawClient["server.session"]) => (input: Endpoint5_31Input) =>
-  preserveEffect<Endpoint5_31Output>()(
+const Endpoint5_34 = (raw: RawClient["server.session"]) => (input: Endpoint5_34Input) =>
+  preserveEffect<Endpoint5_34Output>()(
     raw["session.message"]({ params: { sessionID: input["sessionID"], messageID: input["messageID"] } }).pipe(
       Effect.mapError(mapClientError),
       Effect.map((value) => value.data),
@@ -605,13 +632,13 @@ const adaptGroup5 = (raw: RawClient["server.session"]) => ({
   wait: Endpoint5_18(raw),
   revert: { stage: Endpoint5_19(raw), clear: Endpoint5_20(raw), commit: Endpoint5_21(raw) },
   context: Endpoint5_22(raw),
-  pending: { list: Endpoint5_23(raw) },
-  instructions: { entry: { list: Endpoint5_24(raw), put: Endpoint5_25(raw), remove: Endpoint5_26(raw) } },
-  generate: Endpoint5_27(raw),
-  log: Endpoint5_28(raw),
-  interrupt: Endpoint5_29(raw),
-  background: Endpoint5_30(raw),
-  message: Endpoint5_31(raw),
+  pending: { list: Endpoint5_23(raw), cancel: Endpoint5_24(raw), steer: Endpoint5_25(raw), queue: Endpoint5_26(raw) },
+  instructions: { entry: { list: Endpoint5_27(raw), put: Endpoint5_28(raw), remove: Endpoint5_29(raw) } },
+  generate: Endpoint5_30(raw),
+  log: Endpoint5_31(raw),
+  interrupt: Endpoint5_32(raw),
+  background: Endpoint5_33(raw),
+  message: Endpoint5_34(raw),
 })
 
 const Endpoint6_0 = (raw: RawClient["server.message"]) => (input: Endpoint6_0Input) =>

packages/client/src/promise/generated/client.ts

@@ -58,6 +58,12 @@ import type {
   SessionContextOutput,
   SessionPendingListInput,
   SessionPendingListOutput,
+  SessionPendingCancelInput,
+  SessionPendingCancelOutput,
+  SessionPendingSteerInput,
+  SessionPendingSteerOutput,
+  SessionPendingQueueInput,
+  SessionPendingQueueOutput,
   SessionInstructionsEntryListInput,
   SessionInstructionsEntryListOutput,
   SessionInstructionsEntryPutInput,
@@ -766,6 +772,39 @@ export function make(options: ClientOptions) {
             },
             requestOptions,
           ).then((value) => value.data),
+        cancel: (input: SessionPendingCancelInput, requestOptions?: RequestOptions) =>
+          request<SessionPendingCancelOutput>(
+            {
+              method: "DELETE",
+              path: `/api/session/${encodeURIComponent(input.sessionID)}/pending/${encodeURIComponent(input.inputID)}`,
+              successStatus: 204,
+              declaredStatuses: [409, 404, 401, 400],
+              empty: true,
+            },
+            requestOptions,
+          ),
+        steer: (input: SessionPendingSteerInput, requestOptions?: RequestOptions) =>
+          request<SessionPendingSteerOutput>(
+            {
+              method: "POST",
+              path: `/api/session/${encodeURIComponent(input.sessionID)}/pending/${encodeURIComponent(input.inputID)}/steer`,
+              successStatus: 204,
+              declaredStatuses: [409, 404, 401, 400],
+              empty: true,
+            },
+            requestOptions,
+          ),
+        queue: (input: SessionPendingQueueInput, requestOptions?: RequestOptions) =>
+          request<SessionPendingQueueOutput>(
+            {
+              method: "POST",
+              path: `/api/session/${encodeURIComponent(input.sessionID)}/pending/${encodeURIComponent(input.inputID)}/queue`,
+              successStatus: 204,
+              declaredStatuses: [409, 404, 401, 400],
+              empty: true,
+            },
+            requestOptions,
+          ),
       },
       instructions: {
         entry: {

packages/client/src/promise/generated/types.ts

@@ -502,6 +502,36 @@ export type SessionInputPromoted = {
   data: { sessionID: string; inputID: string }
 }
 
+export type SessionInputCancelled = {
+  id: string
+  created: number
+  metadata?: { [x: string]: any }
+  type: "session.input.cancelled"
+  durable: { aggregateID: string; seq: number; version: 1 }
+  location?: LocationRef
+  data: { sessionID: string; inputID: string }
+}
+
+export type SessionInputSteered = {
+  id: string
+  created: number
+  metadata?: { [x: string]: any }
+  type: "session.input.steered"
+  durable: { aggregateID: string; seq: number; version: 1 }
+  location?: LocationRef
+  data: { sessionID: string; inputID: string }
+}
+
+export type SessionInputQueued = {
+  id: string
+  created: number
+  metadata?: { [x: string]: any }
+  type: "session.input.queued"
+  durable: { aggregateID: string; seq: number; version: 1 }
+  location?: LocationRef
+  data: { sessionID: string; inputID: string }
+}
+
 export type SessionExecutionStarted = {
   id: string
   created: number
@@ -1970,6 +2000,9 @@ export type SessionEventDurable =
   | SessionForked
   | SessionInputPromoted
   | SessionInputAdmitted
+  | SessionInputCancelled
+  | SessionInputSteered
+  | SessionInputQueued
   | SessionExecutionStarted
   | SessionExecutionSucceeded
   | SessionExecutionFailed
@@ -2024,6 +2057,9 @@ export type V2Event =
   | SessionForked
   | SessionInputPromoted
   | SessionInputAdmitted
+  | SessionInputCancelled
+  | SessionInputSteered
+  | SessionInputQueued
   | SessionExecutionStarted
   | SessionExecutionSucceeded
   | SessionExecutionFailed
@@ -3689,6 +3725,27 @@ export type SessionPendingListInput = { readonly sessionID: { readonly sessionID
 
 export type SessionPendingListOutput = { data: Array<SessionPendingInfo> }["data"]
 
+export type SessionPendingCancelInput = {
+  readonly sessionID: { readonly sessionID: string; readonly inputID: string }["sessionID"]
+  readonly inputID: { readonly sessionID: string; readonly inputID: string }["inputID"]
+}
+
+export type SessionPendingCancelOutput = void
+
+export type SessionPendingSteerInput = {
+  readonly sessionID: { readonly sessionID: string; readonly inputID: string }["sessionID"]
+  readonly inputID: { readonly sessionID: string; readonly inputID: string }["inputID"]
+}
+
+export type SessionPendingSteerOutput = void
+
+export type SessionPendingQueueInput = {
+  readonly sessionID: { readonly sessionID: string; readonly inputID: string }["sessionID"]
+  readonly inputID: { readonly sessionID: string; readonly inputID: string }["inputID"]
+}
+
+export type SessionPendingQueueOutput = void
+
 export type SessionInstructionsEntryListInput = { readonly sessionID: { readonly sessionID: string }["sessionID"] }
 
 export type SessionInstructionsEntryListOutput = { data: Array<InstructionEntryInfo> }["data"]

packages/client/test/contract-identity.test.ts

@@ -19,7 +19,7 @@ test("effect entrypoint exposes canonical Schema contracts", () => {
 test("generated Effect API names canonical and composed outputs", async () => {
   const source = await Bun.file(new URL("../src/effect/api/api.ts", import.meta.url)).text()
 
-  expect(source).toContain("export type Endpoint5_3Output = Session.Info")
+  expect(source).toContain("export type Endpoint5_5Output = Session.Info")
   expect(source).toContain("export type Endpoint19_0Output = OpenCodeEvent")
   expect(source).not.toContain("HttpApiClient.ForApi")
 })

packages/client/test/promise.test.ts

@@ -32,6 +32,7 @@ test("exposes every standard HTTP API group", () => {
     "projectCopy",
     "vcs",
     "debug",
+    "migration",
     "websearch",
     "config",
   ])
@@ -356,6 +357,28 @@ test("session.pending.list uses the public HTTP contract", async () => {
   expect(requests).toEqual([{ method: "GET", url: "http://localhost:3000/api/session/ses_test/pending" }])
 })
 
+test("session.pending mutations use the public HTTP contract", async () => {
+  const requests: Array<{ method: string; url: string }> = []
+  const client = OpenCode.make({
+    baseUrl: "http://localhost:3000",
+    fetch: async (input, init) => {
+      const request = input instanceof Request ? input : new Request(input, init)
+      requests.push({ method: request.method, url: request.url })
+      return new Response(null, { status: 204 })
+    },
+  })
+
+  await client.session.pending.cancel({ sessionID: "ses_test", inputID: "msg_cancel" })
+  await client.session.pending.steer({ sessionID: "ses_test", inputID: "msg_steer" })
+  await client.session.pending.queue({ sessionID: "ses_test", inputID: "msg_queue" })
+
+  expect(requests).toEqual([
+    { method: "DELETE", url: "http://localhost:3000/api/session/ses_test/pending/msg_cancel" },
+    { method: "POST", url: "http://localhost:3000/api/session/ses_test/pending/msg_steer/steer" },
+    { method: "POST", url: "http://localhost:3000/api/session/ses_test/pending/msg_queue/queue" },
+  ])
+})
+
 test("event.subscribe exposes the Promise event stream wire projection", async () => {
   const client = OpenCode.make({
     baseUrl: "http://localhost:3000",

packages/core/package.json

@@ -17,6 +17,7 @@
     "opencode": "./bin/opencode"
   },
   "exports": {
+    "./environment": "./src/environment/index.ts",
     "./session/runner": "./src/session/runner/index.ts",
     "./instructions": "./src/instructions/index.ts",
     "./*": "./src/*.ts"
@@ -117,6 +118,7 @@
     "immer": "11.1.4",
     "ignore": "7.0.5",
     "jsonc-parser": "3.3.1",
+    "mime-types": "3.0.2",
     "turndown": "7.2.0",
     "tree-sitter-bash": "0.25.0",
     "tree-sitter-powershell": "0.25.10",

packages/core/src/config/plugin/provider.ts

@@ -13,12 +13,14 @@ export const Plugin = define({
     const config = yield* Config.Service
     const loaded = { entries: yield* config.entries() }
     yield* ctx.integration.transform((integrations) => {
-      const configuredIntegrations = new Set(
-        configuredProviders(loaded.entries).flatMap(([id, provider]) => (provider.env === undefined ? [] : [id])),
-      )
       for (const [id, provider] of configuredProviders(loaded.entries)) {
         const integrationID = id
-        if (!configuredIntegrations.has(id) && !integrations.get(integrationID)) continue
+        if (!integrations.get(integrationID)) {
+          integrations.method.update({
+            integrationID,
+            method: { type: "key", label: "Manually enter API Key" },
+          })
+        }
         integrations.update(integrationID, (integration) => {
           integration.name = provider.name ?? integration.name
         })

packages/core/src/environment/driver.ts

@@ -0,0 +1,9 @@
+import type { ChildProcessSpawner } from "effect/unstable/process/ChildProcessSpawner"
+import type { FilesImpl } from "./files"
+
+export interface Driver {
+  readonly spawner: ChildProcessSpawner["Service"]
+  readonly overrides?: Partial<FilesImpl>
+}
+
+export * as EnvironmentDriver from "./driver"

packages/core/src/environment/environment.ts

@@ -0,0 +1,26 @@
+import { CrossSpawnSpawner } from "@opencode-ai/util/cross-spawn-spawner"
+import { makeLocationNode } from "@opencode-ai/util/effect/app-node"
+import { Context, Effect, Layer } from "effect"
+import { ChildProcessSpawner } from "effect/unstable/process/ChildProcessSpawner"
+import type { Files } from "./files"
+import { makeFiles } from "./index"
+import { makeLocalDriver } from "./local"
+
+export interface Interface {
+  readonly files: Files
+  readonly spawner: ChildProcessSpawner["Service"]
+}
+
+export class Service extends Context.Service<Service, Interface>()("@opencode/Environment") {}
+
+const layer = Layer.effect(
+  Service,
+  Effect.gen(function* () {
+    const spawner = yield* ChildProcessSpawner
+    return Service.of({ files: makeFiles(makeLocalDriver(spawner)), spawner })
+  }),
+)
+
+export const node = makeLocationNode({ service: Service, layer, deps: [CrossSpawnSpawner.node] })
+
+export * as EnvironmentService from "./environment"

packages/core/src/environment/exec-defaults.ts

@@ -0,0 +1,192 @@
+import { Effect, Stream } from "effect"
+import { ChildProcess } from "effect/unstable/process"
+import type { ChildProcessSpawner } from "effect/unstable/process/ChildProcessSpawner"
+import { collectStream } from "@opencode-ai/util/process"
+import { Failed, NotFound, WrongKind, type FileInfo, type FileType, type FilesImpl } from "./files"
+
+/**
+ * Files derived from spawning processes: one process per intent, "$1" is
+ * always the target path. Scripts report classification through an exit-code
+ * protocol (44/45/46) so failures never require parsing localized error text;
+ * LC_ALL=C pins the one stderr match that remains. Requires GNU coreutils and
+ * findutils in the target image — BSD and busybox userlands will not work.
+ * Malformed output from these scripts is our own bug and dies as a defect.
+ */
+
+const MAX_DATA_BYTES = 64 * 1024 * 1024
+const MAX_ERROR_BYTES = 64 * 1024
+const NOT_FOUND = 44
+const WRONG_KIND = 45
+const FAILED = 46
+const TAB = "\t"
+
+const loadMetadata = (flags = "") => `
+metadata=$(stat ${flags} -c '%F${TAB}%s${TAB}%Y' -- "$1" 2>&1) || {
+  case "$metadata" in
+    *'No such file or directory'*|*'Not a directory'*) exit ${NOT_FOUND} ;;
+    *) printf '%s' "$metadata" >&2; exit ${FAILED} ;;
+  esac
+}
+`
+
+const statScript = `
+${loadMetadata()}
+printf '%s\n' "$metadata"
+`
+
+const readScript = `
+${loadMetadata("-L")}
+kind=\${metadata%%${TAB}*}
+if [ "$kind" != 'regular file' ] && [ "$kind" != 'regular empty file' ]; then
+  printf '%s' "$kind" >&2
+  exit ${WRONG_KIND}
+fi
+printf '%s\n' "$metadata"
+if [ "$2" = range ]; then
+  dd if="$1" iflag=skip_bytes,count_bytes skip="$3" count="$4" status=none
+else
+  cat -- "$1"
+fi
+`
+
+const listScript = `
+${loadMetadata("-L")}
+kind=\${metadata%%${TAB}*}
+if [ "$kind" != directory ]; then
+  printf '%s' "$kind" >&2
+  exit ${WRONG_KIND}
+fi
+find -H "$1" -mindepth 1 -maxdepth 1 -printf '%y\\0%f\\0'
+`
+
+const moveScript = `
+${loadMetadata()}
+mv -- "$1" "$2"
+`
+
+interface Result {
+  readonly exitCode: number
+  readonly stdout: Uint8Array
+  readonly stderr: Uint8Array
+}
+
+export const execDefaults = (spawner: ChildProcessSpawner["Service"]): FilesImpl => {
+  const run = (
+    path: string,
+    script: string,
+    args: ReadonlyArray<string> = [],
+    stdin?: Uint8Array,
+  ): Effect.Effect<Result, Failed> =>
+    Effect.scoped(
+      Effect.gen(function* () {
+        const command = ChildProcess.make("sh", ["-c", script, "sh", path, ...args], {
+          env: { LC_ALL: "C" },
+          extendEnv: true,
+          stdin: stdin === undefined ? undefined : Stream.make(stdin),
+        })
+        const handle = yield* spawner.spawn(command).pipe(Effect.mapError((cause) => new Failed({ path, cause })))
+        const [stdout, stderr, exitCode] = yield* Effect.all(
+          [
+            collectStream(handle.stdout, MAX_DATA_BYTES),
+            collectStream(handle.stderr, MAX_ERROR_BYTES),
+            handle.exitCode,
+          ],
+          { concurrency: "unbounded" },
+        ).pipe(Effect.mapError((cause) => new Failed({ path, cause })))
+        if (stdout.truncated || stderr.truncated) {
+          return yield* new Failed({ path, cause: new Error("Process output exceeded its collection limit") })
+        }
+        return { exitCode, stdout: stdout.buffer, stderr: stderr.buffer }
+      }),
+    )
+
+  const classify = <A>(
+    path: string,
+    result: Result,
+    success: (stdout: Uint8Array) => A,
+  ): Effect.Effect<A, NotFound | WrongKind | Failed> => {
+    if (result.exitCode === 0) return Effect.sync(() => success(result.stdout))
+    if (result.exitCode === NOT_FOUND) return Effect.fail(new NotFound({ path }))
+    if (result.exitCode === WRONG_KIND) {
+      return Effect.fail(new WrongKind({ path, actual: parseType(new TextDecoder().decode(result.stderr)) }))
+    }
+    return Effect.fail(processFailure(path, result))
+  }
+
+  const complete = (path: string, result: Result) =>
+    result.exitCode === 0 ? Effect.void : Effect.fail(processFailure(path, result))
+
+  return {
+    stat: (path) => run(path, statScript).pipe(Effect.flatMap((result) => classifyPlain(path, result, parseInfo))),
+    read: (path, range) =>
+      run(
+        path,
+        readScript,
+        range === undefined ? ["whole"] : ["range", String(range.offset), String(range.length)],
+      ).pipe(
+        Effect.flatMap((result) =>
+          classify(path, result, (stdout) => {
+            const newline = stdout.indexOf(10)
+            if (newline < 0) throw new Error("Missing read metadata header")
+            return {
+              info: parseInfo(stdout.slice(0, newline)),
+              bytes: stdout.slice(newline + 1),
+            }
+          }),
+        ),
+      ),
+    write: (path, bytes) =>
+      run(path, `mkdir -p "$(dirname "$1")" && cat > "$1"`, [], bytes).pipe(
+        Effect.flatMap((result) => complete(path, result)),
+      ),
+    list: (path) => run(path, listScript).pipe(Effect.flatMap((result) => classify(path, result, parseList))),
+    remove: (path) => run(path, `rm -rf -- "$1"`).pipe(Effect.flatMap((result) => complete(path, result))),
+    move: (from, to) =>
+      run(from, moveScript, [to]).pipe(Effect.flatMap((result) => classifyPlain(from, result, () => undefined))),
+    mkdir: (path) => run(path, `mkdir -p -- "$1"`).pipe(Effect.flatMap((result) => complete(path, result))),
+  }
+}
+
+/** `classify` for scripts whose protocol never reports WrongKind. */
+const classifyPlain = <A>(
+  path: string,
+  result: Result,
+  success: (stdout: Uint8Array) => A,
+): Effect.Effect<A, NotFound | Failed> => {
+  if (result.exitCode === 0) return Effect.sync(() => success(result.stdout))
+  if (result.exitCode === NOT_FOUND) return Effect.fail(new NotFound({ path }))
+  return Effect.fail(processFailure(path, result))
+}
+
+const processFailure = (path: string, result: Result) =>
+  new Failed({
+    path,
+    cause: new Error(new TextDecoder().decode(result.stderr).trim() || `Process exited with code ${result.exitCode}`),
+  })
+
+const parseInfo = (bytes: Uint8Array): FileInfo => {
+  const [rawType, rawSize, rawMtime] = new TextDecoder().decode(bytes).trim().split(TAB)
+  const size = Number(rawSize)
+  const mtimeMs = Number(rawMtime) * 1_000
+  if (!rawType || !Number.isFinite(size) || !Number.isFinite(mtimeMs)) throw new Error("Invalid stat output")
+  return { type: parseType(rawType), size, mtimeMs }
+}
+
+const parseType = (value: string): FileType => {
+  if (value === "regular file" || value === "regular empty file" || value === "f") return "file"
+  if (value === "directory" || value === "d") return "directory"
+  if (value === "symbolic link" || value === "l") return "symlink"
+  return "other"
+}
+
+const parseList = (bytes: Uint8Array) => {
+  const fields = new TextDecoder().decode(bytes).split("\0")
+  fields.pop()
+  if (fields.length % 2 !== 0) throw new Error("Invalid find output")
+  return Array.from({ length: fields.length / 2 }, (_, index) => ({
+    name: fields[index * 2 + 1],
+    type: parseType(fields[index * 2]),
+  }))
+}
+
+export * as EnvironmentExecDefaults from "./exec-defaults"

packages/core/src/environment/files.ts

@@ -0,0 +1,70 @@
+import { Effect, Schema } from "effect"
+
+export const FileType = Schema.Literals(["file", "directory", "symlink", "other"])
+export type FileType = typeof FileType.Type
+
+export interface FileInfo {
+  readonly type: FileType
+  readonly size: number
+  readonly mtimeMs: number
+}
+
+export interface DirEntry {
+  readonly name: string
+  readonly type: FileType
+}
+
+export class NotFound extends Schema.TaggedErrorClass<NotFound>()("Environment.NotFound", {
+  path: Schema.String,
+}) {}
+
+export class WrongKind extends Schema.TaggedErrorClass<WrongKind>()("Environment.WrongKind", {
+  path: Schema.String,
+  actual: FileType,
+}) {}
+
+export class Failed extends Schema.TaggedErrorClass<Failed>()("Environment.Failed", {
+  path: Schema.String,
+  cause: Schema.Defect(),
+}) {}
+
+export interface FilesImpl {
+  /**
+   * Content operations (`read`, `list`) follow final symlinks; metadata operations (`stat` and entry
+   * tags returned by `list`) do not. `info` describes the target file whose bytes are returned.
+   * The process-backed default caps collected output at 64 MiB; larger whole-file reads fail with
+   * `Failed`, so callers must use ranges for larger files.
+   */
+  readonly read: (
+    path: string,
+    range?: { readonly offset: number; readonly length: number },
+  ) => Effect.Effect<{ readonly info: FileInfo; readonly bytes: Uint8Array }, NotFound | WrongKind | Failed>
+  readonly write: (path: string, bytes: Uint8Array) => Effect.Effect<void, Failed>
+  /** Describes the path entry itself, so a final symlink is reported as `symlink` rather than followed. */
+  readonly stat: (path: string) => Effect.Effect<FileInfo, NotFound | Failed>
+  /** Follows a final symlink to the listed directory while preserving each returned entry's own type. */
+  readonly list: (path: string) => Effect.Effect<ReadonlyArray<DirEntry>, NotFound | WrongKind | Failed>
+  readonly remove: (path: string) => Effect.Effect<void, Failed>
+  readonly move: (from: string, to: string) => Effect.Effect<void, NotFound | Failed>
+  readonly mkdir: (path: string) => Effect.Effect<void, Failed>
+}
+
+export interface Files extends FilesImpl {}
+
+/**
+ * Derives a follow-stat kind from the lstat-like Files contract. A dangling
+ * symlink fails with `NotFound`.
+ */
+export const typeFollowing = (files: Files, path: string) =>
+  files.stat(path).pipe(
+    Effect.flatMap((info) =>
+      info.type === "symlink"
+        ? files.read(path, { offset: 0, length: 0 }).pipe(
+            Effect.map((result) => result.info.type),
+            Effect.catchTag("Environment.WrongKind", (error) => Effect.succeed(error.actual)),
+          )
+        : Effect.succeed(info.type),
+    ),
+  )
+
+export * as EnvironmentFiles from "./files"

packages/core/src/environment/index.ts

@@ -0,0 +1,27 @@
+export * as Environment from "./index"
+
+export { type Driver } from "./driver"
+export {
+  type DirEntry,
+  Failed,
+  type FileInfo,
+  type Files,
+  type FilesImpl,
+  type FileType,
+  NotFound,
+  typeFollowing,
+  WrongKind,
+} from "./files"
+export { execDefaults } from "./exec-defaults"
+export { makeLocalDriver } from "./local"
+export { makeMemoryDriver, type MemoryDriver } from "./memory"
+export { type Interface, node, Service } from "./environment"
+
+import type { Driver } from "./driver"
+import { execDefaults } from "./exec-defaults"
+import type { Files } from "./files"
+
+export const makeFiles = (driver: Driver): Files => ({
+  ...execDefaults(driver.spawner),
+  ...driver.overrides,
+})

packages/core/src/environment/local.ts

@@ -0,0 +1,103 @@
+import fs from "node:fs/promises"
+import path from "node:path"
+import { Effect } from "effect"
+import type { ChildProcessSpawner } from "effect/unstable/process/ChildProcessSpawner"
+import type { Driver } from "./driver"
+import { Failed, NotFound, WrongKind, type FileInfo, type FilesImpl, type FileType } from "./files"
+
+/**
+ * The host filesystem binding. Deliberately raw node:fs rather than effect's
+ * FileSystem service or FSUtil: the contract needs lstat semantics (stat
+ * reports "symlink") and typed directory entries, and effect's node
+ * FileSystem provides neither — its stat always follows symlinks and
+ * readDirectory returns names only. FSUtil hits the same gap and its
+ * readDirectoryEntries already bypasses to raw node readdir internally.
+ * Nothing above the environment seam touches node:fs.
+ */
+export const makeLocalDriver = (spawner: ChildProcessSpawner["Service"]): Driver => {
+  const overrides: FilesImpl = {
+    read: (value, range) =>
+      Effect.gen(function* () {
+        const info = yield* stat(value, true)
+        if (info.type !== "file") return yield* new WrongKind({ path: value, actual: info.type })
+        if (range === undefined) {
+          const bytes = yield* attempt(value, () => fs.readFile(value), true)
+          return { info, bytes }
+        }
+        const bytes = yield* attempt(
+          value,
+          async () => {
+            const handle = await fs.open(value, "r")
+            try {
+              const buffer = new Uint8Array(range.length)
+              const result = await handle.read(buffer, 0, range.length, range.offset)
+              return buffer.subarray(0, result.bytesRead)
+            } finally {
+              await handle.close()
+            }
+          },
+          true,
+        )
+        return { info, bytes }
+      }),
+    stat: (value) => stat(value, false),
+    list: (value) =>
+      Effect.gen(function* () {
+        const info = yield* stat(value, true)
+        if (info.type !== "directory") return yield* new WrongKind({ path: value, actual: info.type })
+        const entries = yield* attempt(value, () => fs.readdir(value, { withFileTypes: true }), true)
+        return entries.map((entry) => ({ name: entry.name, type: fileType(entry) }))
+      }),
+    write: (value, bytes) =>
+      attempt(value, async () => {
+        await fs.mkdir(path.dirname(value), { recursive: true })
+        await fs.writeFile(value, bytes)
+      }),
+    remove: (value) => attempt(value, () => fs.rm(value, { recursive: true, force: true })),
+    move: (from, to) =>
+      Effect.gen(function* () {
+        yield* stat(from, false)
+        const destination = yield* stat(to, false).pipe(
+          Effect.map((info) => (info.type === "directory" ? path.join(to, path.basename(from)) : to)),
+          Effect.catchIf(
+            (error) => error instanceof NotFound,
+            () => Effect.succeed(to),
+          ),
+        )
+        yield* attempt(from, () => fs.rename(from, destination))
+      }),
+    mkdir: (value) => attempt(value, () => fs.mkdir(value, { recursive: true }).then(() => undefined)),
+  }
+
+  return { spawner, overrides }
+}
+
+const stat = (value: string, follow: boolean) =>
+  attempt(value, () => (follow ? fs.stat(value) : fs.lstat(value)), true).pipe(
+    Effect.map((stats): FileInfo => ({ type: fileType(stats), size: stats.size, mtimeMs: stats.mtimeMs })),
+  )
+
+const fileType = (entry: { isFile(): boolean; isDirectory(): boolean; isSymbolicLink(): boolean }): FileType => {
+  if (entry.isFile()) return "file"
+  if (entry.isDirectory()) return "directory"
+  if (entry.isSymbolicLink()) return "symlink"
+  return "other"
+}
+
+function attempt<A>(value: string, run: () => Promise<A>): Effect.Effect<A, Failed>
+function attempt<A>(value: string, run: () => Promise<A>, missing: true): Effect.Effect<A, NotFound | Failed>
+function attempt<A>(value: string, run: () => Promise<A>, missing = false) {
+  return Effect.tryPromise({
+    try: run,
+    catch: (cause) =>
+      missing && isMissing(cause) ? new NotFound({ path: value }) : new Failed({ path: value, cause }),
+  })
+}
+
+const isMissing = (cause: unknown) =>
+  cause !== null &&
+  typeof cause === "object" &&
+  "code" in cause &&
+  (cause.code === "ENOENT" || cause.code === "ENOTDIR")
+
+export * as EnvironmentLocal from "./local"

packages/core/src/environment/memory.ts

@@ -0,0 +1,168 @@
+import path from "node:path"
+import { Effect, PlatformError } from "effect"
+import { make } from "effect/unstable/process/ChildProcessSpawner"
+import type { Driver } from "./driver"
+import { Failed, NotFound, WrongKind, type FileInfo, type FilesImpl, type FileType } from "./files"
+
+type Node =
+  | { readonly type: "file"; readonly bytes: Uint8Array; readonly mtimeMs: number }
+  | { readonly type: "directory"; readonly mtimeMs: number }
+  | { readonly type: "symlink"; readonly target: string; readonly mtimeMs: number }
+
+export interface MemoryDriver extends Driver {
+  readonly symlink: (target: string, path: string) => Effect.Effect<void, Failed>
+}
+
+export const makeMemoryDriver = (): MemoryDriver => {
+  const nodes = new Map<string, Node>([["/", { type: "directory", mtimeMs: Date.now() }]])
+  const key = (value: string) => path.posix.resolve("/", value)
+  const info = (node: Node): FileInfo => ({
+    type: node.type,
+    size:
+      node.type === "file"
+        ? node.bytes.length
+        : node.type === "symlink"
+          ? new TextEncoder().encode(node.target).length
+          : 0,
+    mtimeMs: node.mtimeMs,
+  })
+  const resolveKey = (value: string, followFinal: boolean, seen = new Set<string>()): string | undefined => {
+    const normalized = key(value)
+    const parts = normalized.split("/").filter(Boolean)
+    const base = "/"
+    const walk = (current: string, index: number): string | undefined => {
+      if (index === parts.length) return current
+      const part = parts[index]
+      const candidate = path.posix.join(current, part)
+      const node = nodes.get(candidate)
+      if (node?.type !== "symlink" || (!followFinal && index === parts.length - 1)) return walk(candidate, index + 1)
+      if (seen.has(candidate)) return undefined
+      seen.add(candidate)
+      const target = path.posix.resolve(path.posix.dirname(candidate), node.target)
+      return resolveKey(path.posix.join(target, ...parts.slice(index + 1)), followFinal, seen)
+    }
+    return walk(base, 0)
+  }
+  const lookup = (value: string) => nodes.get(resolveKey(value, false) ?? key(value))
+  const requireParent = (value: string) => {
+    const parentPath = path.posix.dirname(key(value))
+    const parent = nodes.get(resolveKey(parentPath, true) ?? parentPath)
+    if (!parent) throw new Error(`Parent directory does not exist: ${path.posix.dirname(value)}`)
+    if (parent.type !== "directory") throw new Error(`Parent is not a directory: ${path.posix.dirname(value)}`)
+  }
+  const mkdirSync = (value: string) => {
+    const target = resolveKey(value, false) ?? key(value)
+    const existing = nodes.get(target)
+    if (existing?.type === "directory") return
+    if (existing) throw new Error(`Path is not a directory: ${value}`)
+    const parent = path.posix.dirname(target)
+    if (parent !== target) mkdirSync(parent)
+    nodes.set(target, { type: "directory", mtimeMs: Date.now() })
+  }
+  const failed = (value: string, cause: unknown) => new Failed({ path: value, cause })
+  const overrides: FilesImpl = {
+    stat: (value) => {
+      const node = lookup(value)
+      return node ? Effect.succeed(info(node)) : Effect.fail(new NotFound({ path: value }))
+    },
+    read: (value, range) => {
+      const original = lookup(value)
+      if (!original) return Effect.fail(new NotFound({ path: value }))
+      if (original.type === "directory") return Effect.fail(new WrongKind({ path: value, actual: "directory" }))
+      const resolved = resolveKey(value, true)
+      const node = resolved === undefined ? undefined : nodes.get(resolved)
+      if (!node) return Effect.fail(new NotFound({ path: value }))
+      if (node.type !== "file") return Effect.fail(new WrongKind({ path: value, actual: node.type }))
+      const bytes = range === undefined ? node.bytes : node.bytes.subarray(range.offset, range.offset + range.length)
+      return Effect.succeed({ info: info(node), bytes: bytes.slice() })
+    },
+    write: (value, bytes) =>
+      Effect.try({
+        try: () => {
+          mkdirSync(path.posix.dirname(key(value)))
+          const existing = lookup(value)
+          if (existing?.type === "directory") throw new Error(`Path is a directory: ${value}`)
+          const target = existing?.type === "symlink" ? resolveKey(value, true) : resolveKey(value, false)
+          if (!target) throw new Error(`Cannot resolve symlink: ${value}`)
+          requireParent(target)
+          nodes.set(target, { type: "file", bytes: bytes.slice(), mtimeMs: Date.now() })
+        },
+        catch: (cause) => failed(value, cause),
+      }),
+    list: (value) => {
+      const target = resolveKey(value, true) ?? key(value)
+      const node = nodes.get(target)
+      if (!node) return Effect.fail(new NotFound({ path: value }))
+      if (node.type !== "directory") return Effect.fail(new WrongKind({ path: value, actual: node.type }))
+      const entries = [...nodes.entries()]
+        .filter(([entry]) => entry !== target && path.posix.dirname(entry) === target)
+        .map(([entry, child]) => ({ name: path.posix.basename(entry), type: child.type satisfies FileType }))
+        .sort((a, b) => a.name.localeCompare(b.name))
+      return Effect.succeed(entries)
+    },
+    remove: (value) =>
+      Effect.sync(() => {
+        const target = resolveKey(value, false) ?? key(value)
+        for (const entry of nodes.keys()) {
+          if (entry === target || entry.startsWith(`${target}/`)) nodes.delete(entry)
+        }
+      }),
+    move: (from, to) => {
+      const source = resolveKey(from, false) ?? key(from)
+      const node = nodes.get(source)
+      if (!node) return Effect.fail(new NotFound({ path: from }))
+      return Effect.try({
+        try: () => {
+          const requested = resolveKey(to, false) ?? key(to)
+          const destination =
+            nodes.get(requested)?.type === "directory"
+              ? path.posix.join(requested, path.posix.basename(source))
+              : requested
+          if (node.type === "directory" && destination.startsWith(`${source}/`)) {
+            throw new Error(`Cannot move a directory into itself: ${from}`)
+          }
+          const existing = nodes.get(destination)
+          if (node.type === "directory" && existing && existing.type !== "directory") {
+            throw new Error(`Cannot overwrite a non-directory with a directory: ${to}`)
+          }
+          requireParent(destination)
+          const moved = [...nodes.entries()].filter(([entry]) => entry === source || entry.startsWith(`${source}/`))
+          for (const [entry] of moved) nodes.delete(entry)
+          for (const [entry, child] of moved) nodes.set(`${destination}${entry.slice(source.length)}`, child)
+        },
+        catch: (cause) => failed(from, cause),
+      })
+    },
+    mkdir: (value) => Effect.try({ try: () => mkdirSync(value), catch: (cause) => failed(value, cause) }),
+  }
+
+  const spawner = make((command) =>
+    Effect.suspend(() => {
+      const description = command._tag === "StandardCommand" ? command.command : "pipeline"
+      return Effect.fail(
+        PlatformError.systemError({
+          _tag: "Unknown",
+          module: "EnvironmentMemory",
+          method: "spawn",
+          pathOrDescriptor: description,
+          cause: failed(description, new Error("The memory driver cannot spawn processes")),
+        }),
+      )
+    }),
+  )
+
+  return {
+    spawner,
+    overrides,
+    symlink: (target, value) =>
+      Effect.try({
+        try: () => {
+          requireParent(value)
+          nodes.set(resolveKey(value, false) ?? key(value), { type: "symlink", target, mtimeMs: Date.now() })
+        },
+        catch: (cause) => failed(value, cause),
+      }),
+  }
+}
+
+export * as EnvironmentMemory from "./memory"

packages/core/src/file-mutation.ts

@@ -5,6 +5,8 @@ import { Context, Effect, Layer } from "effect"
 import { KeyedMutex } from "./effect/keyed-mutex"
 import { FSUtil } from "@opencode-ai/util/fs-util"
 import { Bom } from "@opencode-ai/util/bom"
+import { Environment } from "./environment"
+import type { Files } from "./environment"
 
 export interface Target {
   readonly absolute: string
@@ -29,13 +31,36 @@ export interface WriteResult {
 }
 
 export interface Interface {
-  readonly write: (input: WriteInput) => Effect.Effect<WriteResult, FSUtil.Error>
+  /** Serialize a complete read/prepare/write mutation transaction by resolved path. */
+  readonly withLock: (
+    targets: ReadonlyArray<string>,
+  ) => <A, E, R>(effect: Effect.Effect<A, E, R>) => Effect.Effect<A, E, R>
+  readonly write: (input: WriteInput) => Effect.Effect<WriteResult, Environment.Failed>
   /** Write text while retaining an existing UTF-8 BOM and emitting at most one BOM. */
-  readonly writeTextPreservingBom: (input: TextWriteInput) => Effect.Effect<WriteResult, FSUtil.Error>
+  readonly writeTextPreservingBom: (
+    input: TextWriteInput,
+  ) => Effect.Effect<WriteResult, Environment.WrongKind | Environment.Failed>
 }
 
 export class Service extends Context.Service<Service, Interface>()("@opencode/FileMutation") {}
 
+export const readText = Effect.fn("FileMutation.readText")(function* (files: Files, target: string) {
+  return Bom.decodeBytes((yield* files.read(target)).bytes)
+})
+
+export const syncTextBom = Effect.fn("FileMutation.syncTextBom")(function* (
+  files: Files,
+  target: string,
+  bom: boolean,
+) {
+  const synced = Bom.syncBytes((yield* files.read(target)).bytes, bom)
+  if (synced.bytes) yield* files.write(target, synced.bytes)
+  return synced.text
+})
+
+/** Share transaction locks across Location graphs that address the same file. */
+const transactionLocks = KeyedMutex.makeUnsafe<string>()
+
 /**
  * Serialize file changes by absolute target. Conditional writes compare and
  * write under the same process-local lock so cooperating OpenCode mutations do
@@ -44,8 +69,12 @@ export class Service extends Context.Service<Service, Interface>()("@opencode/Fi
 const layer = Layer.effect(
   Service,
   Effect.gen(function* () {
-    const fs = yield* FSUtil.Service
+    const environment = yield* Environment.Service
     const locks = KeyedMutex.makeUnsafe<string>()
+    const withLock: Interface["withLock"] = (targets) => (effect) =>
+      [...new Set(targets.map(FSUtil.resolve))]
+        .sort()
+        .reduceRight((result, target) => transactionLocks.withLock(target)(result), effect)
     const withTargetLock =
       (target: Target) =>
       <A, E, R>(effect: Effect.Effect<A, E, R>) =>
@@ -61,8 +90,14 @@ const layer = Layer.effect(
     const write = Effect.fn("FileMutation.write")((input: WriteInput) =>
       withTargetLock(input.target)(
         Effect.gen(function* () {
-          const existed = yield* fs.exists(input.target.absolute)
-          yield* fs.writeWithDirs(input.target.absolute, input.content)
+          const existed = yield* environment.files.stat(input.target.absolute).pipe(
+            Effect.as(true),
+            Effect.catchTag("Environment.NotFound", () => Effect.succeed(false)),
+          )
+          yield* environment.files.write(
+            input.target.absolute,
+            typeof input.content === "string" ? new TextEncoder().encode(input.content) : input.content,
+          )
           return writeResult(input.target, existed)
         }),
       ),
@@ -72,23 +107,24 @@ const layer = Layer.effect(
       withTargetLock(input.target)(
         Effect.gen(function* () {
           const next = Bom.split(input.content)
-          const current = yield* fs
-            .readFile(input.target.absolute)
-            .pipe(Effect.catchReason("PlatformError", "NotFound", () => Effect.succeed(undefined)))
-          yield* fs.writeWithDirs(
+          const current = yield* environment.files.read(input.target.absolute, { offset: 0, length: 3 }).pipe(
+            Effect.map((result) => result.bytes),
+            Effect.catchTag("Environment.NotFound", () => Effect.succeed(undefined)),
+          )
+          yield* environment.files.write(
             input.target.absolute,
-            Bom.join(next.text, Boolean(current && Bom.has(current)) || next.bom),
+            new TextEncoder().encode(Bom.join(next.text, Boolean(current && Bom.has(current)) || next.bom)),
           )
           return writeResult(input.target, current !== undefined)
         }),
       ),
     )
 
-    return Service.of({ write, writeTextPreservingBom })
+    return Service.of({ withLock, write, writeTextPreservingBom })
   }),
 )
 
-export const node = makeLocationNode({ service: Service, layer, deps: [FSUtil.node] })
+export const node = makeLocationNode({ service: Service, layer, deps: [Environment.node] })
 
 /**
  * Deferred until the corresponding integrations exist.

packages/core/src/filesystem/location-watcher.ts

@@ -11,15 +11,6 @@ import { FSUtil } from "@opencode-ai/util/fs-util"
 import { Git } from "../git"
 import { Location } from "../location"
 import { Watcher } from "./watcher"
-import { Ignore } from "./ignore"
-import { Protected } from "./protected"
-
-function protecteds(dir: string) {
-  return Protected.paths().filter((item) => {
-    const relative = path.relative(dir, item)
-    return relative !== "" && !relative.startsWith("..") && !path.isAbsolute(relative)
-  })
-}
 
 export interface Interface {}
 
@@ -44,19 +35,6 @@ const layer = Layer.effect(
       const config = (yield* configService.entries())
         .filter((entry): entry is Document => entry.type === "document")
         .flatMap((item) => item.info.watcher?.ignore ?? [])
-      const home = Protected.isHome(location.directory)
-
-      if (!home && location.vcs) {
-        const updates = yield* watcher.subscribe({
-          path: location.directory,
-          type: "directory",
-          ignore: [...Ignore.PATTERNS, ...config, ...protecteds(location.directory)],
-        })
-        yield* updates.pipe(Stream.runForEach(publish), Effect.forkScoped)
-      }
-      if (home) {
-        yield* Effect.logInfo("location watcher skipped home directory", { directory: location.directory })
-      }
 
       if (location.vcs?.type === "git") {
         const resolved = (yield* git.repo.discover(location.directory))?.gitDirectory
@@ -64,10 +42,7 @@ const layer = Layer.effect(
           ? yield* fs.realPath(resolved).pipe(Effect.catch(() => Effect.succeed(resolved)))
           : undefined
         if (vcs && !config.includes(".git") && !config.includes(vcs) && (!resolved || !config.includes(resolved))) {
-          const ignore = (yield* fs.readDirectoryEntries(vcs).pipe(Effect.catch(() => Effect.succeed([])))).flatMap(
-            (entry) => (entry.name === "HEAD" ? [] : [entry.name]),
-          )
-          const updates = yield* watcher.subscribe({ path: vcs, type: "directory", ignore })
+          const updates = yield* watcher.subscribe({ path: path.join(vcs, "HEAD"), type: "file" })
           yield* updates.pipe(Stream.runForEach(publish), Effect.forkScoped)
         }
       }

packages/core/src/location-services.ts

@@ -8,6 +8,7 @@ import { LayerNode } from "@opencode-ai/util/effect/layer-node"
 import { Node } from "@opencode-ai/util/effect/app-node"
 import { Bus } from "./bus"
 import { FileMutation } from "./file-mutation"
+import { Environment } from "./environment"
 import { Formatter } from "./formatter"
 import { FileSystem } from "./filesystem"
 import { FileSystemSearch } from "./filesystem/search"
@@ -53,6 +54,7 @@ export { LocationServiceMap } from "./location-service-map"
 
 const locationServiceNodes = [
   Location.node,
+  Environment.node,
   Config.node,
   Agent.node,
   Command.node,

packages/core/src/plugin/internal.ts

@@ -16,6 +16,7 @@ import { ConfigReferencePlugin } from "../config/plugin/reference"
 import { ConfigSkillPlugin } from "../config/plugin/skill"
 import { ConfigWebSearchPlugin } from "../config/plugin/websearch"
 import { Bus } from "../bus"
+import { Environment } from "../environment"
 import { FileMutation } from "../file-mutation"
 import { Formatter } from "../formatter"
 import { Form } from "../form"
@@ -70,6 +71,7 @@ const services = Effect.fn("PluginInternal.services")(function* () {
   const config = yield* Config.Service
   const credential = yield* Credential.Service
   const bus = yield* Bus.Service
+  const environment = yield* Environment.Service
   const mutation = yield* FileMutation.Service
   const formatter = yield* Formatter.Service
   const filesystem = yield* FileSystem.Service
@@ -102,6 +104,7 @@ const services = Effect.fn("PluginInternal.services")(function* () {
     Context.make(Config.Service, config),
     Context.make(Credential.Service, credential),
     Context.make(Bus.Service, bus),
+    Context.make(Environment.Service, environment),
     Context.make(FileMutation.Service, mutation),
     Context.make(Formatter.Service, formatter),
     Context.make(FileSystem.Service, filesystem),

packages/core/src/plugin/supervisor.ts

@@ -14,6 +14,7 @@ import { Credential } from "../credential"
 import { makeLocationNode } from "@opencode-ai/util/effect/app-node"
 import { httpClient } from "@opencode-ai/util/effect/app-node-platform"
 import { Bus } from "../bus"
+import { Environment } from "../environment"
 import { FileMutation } from "../file-mutation"
 import { Formatter } from "../formatter"
 import { FileSystem } from "../filesystem"
@@ -282,7 +283,9 @@ const layer = Layer.effect(
     })
     const updates = Stream.merge(
       config.changes().pipe(
-        Stream.filterEffect((update) => Effect.map(config.entries(), (entries) => isPluginSource(entries, update.path))),
+        Stream.filterEffect((update) =>
+          Effect.map(config.entries(), (entries) => isPluginSource(entries, update.path)),
+        ),
         Stream.merge(Stream.fromPubSub(configuredChanges)),
       ),
       bus.subscribe([Event.Updated, SdkPlugins.Updated]),
@@ -320,6 +323,7 @@ export const node = makeLocationNode({
     Config.node,
     Credential.node,
     Bus.node,
+    Environment.node,
     FileMutation.node,
     Formatter.node,
     FileSystem.node,

packages/core/src/plugin/websearch/firecrawl.ts

@@ -0,0 +1,84 @@
+export * as WebSearchFirecrawl from "./firecrawl"
+
+import { define } from "@opencode-ai/plugin/effect/plugin"
+import { Effect, Option, Schema, Scope } from "effect"
+import { HttpClient } from "effect/unstable/http"
+import { App } from "../../app"
+import { WebSearchMcp } from "./mcp"
+
+export const endpoint = "https://mcp.firecrawl.dev/v2/mcp"
+
+const McpInput = Schema.Struct({
+  query: Schema.String,
+  limit: Schema.Number.pipe(Schema.optional),
+})
+
+const McpOutput = Schema.Struct({
+  content: Schema.Array(Schema.Struct({ type: Schema.Literal("text"), text: Schema.String })),
+})
+
+const SearchResponse = Schema.fromJsonString(
+  Schema.Struct({
+    success: Schema.Boolean,
+    data: Schema.Struct({
+      web: Schema.Array(
+        Schema.Struct({
+          url: Schema.String,
+          title: Schema.NullOr(Schema.String).pipe(Schema.optional),
+          description: Schema.NullOr(Schema.String).pipe(Schema.optional),
+        }),
+      ),
+    }),
+  }),
+)
+const decodeSearchResponse = Schema.decodeUnknownOption(SearchResponse)
+
+export const Plugin = define<HttpClient.HttpClient | Scope.Scope>({
+  id: "opencode.websearch.firecrawl",
+  effect: Effect.fn("WebSearchFirecrawl.Plugin")(function* (ctx) {
+    const http = yield* HttpClient.HttpClient
+    yield* ctx.integration.transform((draft) => {
+      draft.update("firecrawl", (integration) => (integration.name = "Firecrawl"))
+      draft.method.update({
+        integrationID: "firecrawl",
+        method: { type: "key", label: "API key (optional)" },
+      })
+      draft.method.update({
+        integrationID: "firecrawl",
+        method: { type: "env", names: ["FIRECRAWL_API_KEY"] },
+      })
+    })
+    yield* ctx.websearch.transform((draft) => {
+      draft.add({
+        id: "firecrawl",
+        name: "Firecrawl",
+        execute: (input) =>
+          Effect.gen(function* () {
+            const connection = yield* ctx.integration.connection.active("firecrawl")
+            const credential = connection ? yield* ctx.integration.connection.resolve(connection) : undefined
+            const result = yield* WebSearchMcp.call(
+              http,
+              endpoint,
+              "firecrawl_search",
+              { input: McpInput, output: McpOutput },
+              { query: input.query, limit: 8 },
+              {
+                "User-Agent": App.useragent(ctx.app),
+                ...(credential?.type === "key" ? { Authorization: `Bearer ${credential.key}` } : {}),
+              },
+            )
+            const content = result?.content.find((item) => item.text)
+            const response = content ? Option.getOrUndefined(decodeSearchResponse(content.text)) : undefined
+            return (
+              response?.data.web.map((item) => ({
+                url: item.url,
+                ...(item.title ? { title: item.title } : {}),
+                ...(item.description ? { content: item.description } : {}),
+                time: {},
+              })) ?? []
+            )
+          }),
+      })
+    })
+  }),
+})

packages/core/src/plugin/websearch/index.ts

@@ -1,4 +1,5 @@
 import { WebSearchExa } from "./exa"
+import { WebSearchFirecrawl } from "./firecrawl"
 import { WebSearchParallel } from "./parallel"
 
-export const WebSearchPlugins = [WebSearchExa.Plugin, WebSearchParallel.Plugin] as const
+export const WebSearchPlugins = [WebSearchExa.Plugin, WebSearchFirecrawl.Plugin, WebSearchParallel.Plugin] as const

packages/core/src/ripgrep.ts

@@ -3,8 +3,9 @@ export * as Ripgrep from "./ripgrep"
 import { Context, Effect, Fiber, Layer, Schema, Stream } from "effect"
 import { ChildProcess } from "effect/unstable/process"
 import { Entry, Match } from "@opencode-ai/schema/filesystem"
-import { makeGlobalNode } from "@opencode-ai/util/effect/app-node"
-import { AppProcess, collectStream, waitForAbort } from "@opencode-ai/util/process"
+import { makeLocationNode } from "@opencode-ai/util/effect/app-node"
+import { collectStream, waitForAbort } from "@opencode-ai/util/process"
+import { Environment } from "./environment"
 import { NonNegativeInt, PositiveInt, RelativePath } from "./schema"
 import { RipgrepBinary } from "./ripgrep/binary"
 
@@ -93,7 +94,7 @@ const isInvalidPattern = (stderr: string) =>
 const layer = Layer.effect(
   Service,
   Effect.gen(function* () {
-    const process = yield* AppProcess.Service
+    const environment = yield* Environment.Service
     const binary = yield* RipgrepBinary.Service
 
     const run = <A>(input: {
@@ -107,7 +108,8 @@ const layer = Layer.effect(
     }) => {
       const program = Effect.scoped(
         Effect.gen(function* () {
-          const handle = yield* process.spawn(
+          // Hosted environments will resolve rg through their driver image; the spawner is the execution seam.
+          const handle = yield* environment.spawner.spawn(
             ChildProcess.make(yield* binary.filepath, input.args, { cwd: input.cwd, extendEnv: true, stdin: "ignore" }),
           )
           const stderrFiber = yield* collectStream(handle.stderr, ERROR_BYTES).pipe(
@@ -275,4 +277,4 @@ const layer = Layer.effect(
   }),
 )
 
-export const node = makeGlobalNode({ service: Service, layer: layer, deps: [RipgrepBinary.node, AppProcess.node] })
+export const node = makeLocationNode({ service: Service, layer, deps: [Environment.node, RipgrepBinary.node] })

packages/core/src/session.ts

@@ -133,6 +133,14 @@ export class CompactionConflictError extends Schema.TaggedErrorClass<CompactionC
 export class BusyError extends Schema.TaggedErrorClass<BusyError>()("Session.BusyError", {
   sessionID: SessionSchema.ID,
 }) {}
+export class PendingInputConflictError extends Schema.TaggedErrorClass<PendingInputConflictError>()(
+  "Session.PendingInputConflictError",
+  {
+    sessionID: SessionSchema.ID,
+    inputID: SessionMessage.ID,
+  },
+) {}
+type PendingInputRef = { readonly sessionID: SessionSchema.ID; readonly inputID: SessionMessage.ID }
 export class SkillNotFoundError extends Schema.TaggedErrorClass<SkillNotFoundError>()("Session.SkillNotFoundError", {
   skill: Skill.ID,
 }) {}
@@ -181,6 +189,9 @@ export interface Interface {
    * unhandled compaction barriers.
    */
   readonly pending: (sessionID: SessionSchema.ID) => Effect.Effect<SessionPending.Info[], NotFoundError>
+  readonly cancelPending: (input: PendingInputRef) => Effect.Effect<void, NotFoundError | PendingInputConflictError>
+  readonly steerPending: (input: PendingInputRef) => Effect.Effect<void, NotFoundError | PendingInputConflictError>
+  readonly queuePending: (input: PendingInputRef) => Effect.Effect<void, NotFoundError | PendingInputConflictError>
   /**
    * Durable, ordered session log read. Replays durable session bus after
    * the exclusive `after` cursor, emits a `Synced` marker at the captured
@@ -318,6 +329,31 @@ const layer = Layer.effect(
         ),
       )
 
+    const pendingConflict = Effect.fn("Session.pendingConflict")(function* (input: PendingInputRef) {
+      yield* result.get(input.sessionID)
+      return yield* new PendingInputConflictError(input)
+    })
+    const mutatePending = (
+      input: PendingInputRef,
+      mutation: (
+        bus: Bus.Interface,
+        input: { readonly id: SessionMessage.ID; readonly sessionID: SessionSchema.ID },
+      ) => Effect.Effect<unknown>,
+      wake = false,
+    ) =>
+      Effect.uninterruptible(
+        Effect.gen(function* () {
+          yield* mutation(bus, { sessionID: input.sessionID, id: input.inputID }).pipe(
+            Effect.catchDefect((defect) =>
+              defect instanceof SessionPending.LifecycleConflict
+                ? pendingConflict(input)
+                : Effect.die(defect),
+            ),
+          )
+          if (wake) yield* execution.wake(input.sessionID)
+        }),
+      )
+
     const result = Service.of({
       create: Effect.fn("Session.create")(function* (input) {
         const sessionID = input.id ?? SessionSchema.ID.create()
@@ -507,6 +543,9 @@ const layer = Layer.effect(
         yield* result.get(sessionID)
         return yield* SessionPending.list(db, sessionID)
       }),
+      cancelPending: Effect.fn("Session.cancelPending")((input) => mutatePending(input, SessionPending.cancel)),
+      steerPending: Effect.fn("Session.steerPending")((input) => mutatePending(input, SessionPending.steer, true)),
+      queuePending: Effect.fn("Session.queuePending")((input) => mutatePending(input, SessionPending.queue)),
       log: (input) =>
         Stream.unwrap(
           result

packages/core/src/session/execution/restart.ts

@@ -2,9 +2,14 @@ export * as SessionRestart from "./restart"
 
 import { Context, Effect, Layer } from "effect"
 import { makeGlobalNode } from "@opencode-ai/util/effect/app-node"
+import { Bus } from "../../bus"
+import { SessionEvent } from "../event"
 import { SessionExecution } from "../execution"
 import { SessionStore } from "../store"
 
+const CONTINUE_AFTER_SERVER_RESTART =
+  "The server restarted while you were working. Continue from where you left off without repeating completed work."
+
 export interface Interface {
   /**
    * Marks every execution active in this process for resumption by the next server start.
@@ -26,6 +31,7 @@ export const layer = Layer.effect(
   Effect.gen(function* () {
     const store = yield* SessionStore.Service
     const execution = yield* SessionExecution.Service
+    const bus = yield* Bus.Service
     return Service.of({
       suspendActiveSessions: Effect.gen(function* () {
         yield* store.suspend(yield* execution.active)
@@ -37,6 +43,11 @@ export const layer = Layer.effect(
           (sessionID) =>
             Effect.gen(function* () {
               if (!(yield* store.consumeSuspended(sessionID))) return
+              yield* bus.publish(SessionEvent.Synthetic, {
+                sessionID,
+                text: CONTINUE_AFTER_SERVER_RESTART,
+                description: "Continuing after restart",
+              })
               // Drain failures are already logged and durably recorded by the execution layer.
               yield* Effect.ignore(execution.resume(sessionID))
             }),
@@ -47,4 +58,8 @@ export const layer = Layer.effect(
   }),
 )
 
-export const node = makeGlobalNode({ service: Service, layer, deps: [SessionStore.node, SessionExecution.node] })
+export const node = makeGlobalNode({
+  service: Service,
+  layer,
+  deps: [SessionStore.node, SessionExecution.node, Bus.node],
+})

packages/core/src/session/message-updater.ts

@@ -90,6 +90,9 @@ export function update(adapter: Adapter, event: SessionEvent.DurableEvent) {
       "session.forked": () => Effect.void,
       "session.input.promoted": () => Effect.void,
       "session.input.admitted": () => Effect.void,
+      "session.input.cancelled": () => Effect.void,
+      "session.input.steered": () => Effect.void,
+      "session.input.queued": () => Effect.void,
       "session.execution.started": () => Effect.void,
       "session.execution.succeeded": () => clearCurrentRetry,
       "session.execution.failed": () => clearCurrentRetry,

packages/core/src/session/pending.ts

@@ -37,6 +37,7 @@ const decodeSynthetic = Schema.decodeUnknownSync(SyntheticData)
 const encodeSynthetic = Schema.encodeSync(SyntheticData)
 const decodeMessage = Schema.decodeUnknownSync(SessionMessage.Info)
 const inboxLocks = KeyedMutex.makeUnsafe<SessionSchema.ID>()
+type PendingRef = { readonly id: SessionMessage.ID; readonly sessionID: SessionSchema.ID }
 
 export class LifecycleConflict extends Schema.TaggedErrorClass<LifecycleConflict>()(
   "SessionPending.LifecycleConflict",
@@ -294,10 +295,7 @@ export const projectCompactionAdmitted = Effect.fn("SessionPending.projectCompac
  */
 export const projectPromoted = Effect.fn("SessionPending.projectPromoted")(function* (
   db: DatabaseService,
-  input: {
-    readonly id: SessionMessage.ID
-    readonly sessionID: SessionSchema.ID
-  },
+  input: PendingRef,
 ) {
   if (yield* compaction(db, input.sessionID)) return yield* Effect.die(new LifecycleConflict({ id: input.id }))
   const deleted = yield* db
@@ -312,6 +310,55 @@ export const projectPromoted = Effect.fn("SessionPending.projectPromoted")(funct
   return stored
 })
 
+export const projectCancelled = Effect.fn("SessionPending.projectCancelled")(function* (
+  db: DatabaseService,
+  input: PendingRef,
+) {
+  const deleted = yield* db
+    .delete(SessionPendingTable)
+    .where(
+      and(
+        eq(SessionPendingTable.id, input.id),
+        eq(SessionPendingTable.session_id, input.sessionID),
+        or(eq(SessionPendingTable.delivery, "queue"), eq(SessionPendingTable.delivery, "steer")),
+      ),
+    )
+    .returning({ id: SessionPendingTable.id })
+    .get()
+    .pipe(Effect.orDie)
+  if (!deleted) return yield* Effect.die(new LifecycleConflict({ id: input.id }))
+})
+
+const projectDelivery = Effect.fn("SessionPending.projectDelivery")(function* (
+  db: DatabaseService,
+  input: PendingRef & { readonly from: Delivery; readonly to: Delivery },
+) {
+  const updated = yield* db
+    .update(SessionPendingTable)
+    .set({ delivery: input.to })
+    .where(
+      and(
+        eq(SessionPendingTable.id, input.id),
+        eq(SessionPendingTable.session_id, input.sessionID),
+        eq(SessionPendingTable.delivery, input.from),
+      ),
+    )
+    .returning({ id: SessionPendingTable.id })
+    .get()
+    .pipe(Effect.orDie)
+  if (!updated) return yield* Effect.die(new LifecycleConflict({ id: input.id }))
+})
+
+export const projectSteered = Effect.fn("SessionPending.projectSteered")(
+  (db: DatabaseService, input: PendingRef) =>
+    projectDelivery(db, { ...input, from: "queue", to: "steer" }),
+)
+
+export const projectQueued = Effect.fn("SessionPending.projectQueued")(
+  (db: DatabaseService, input: PendingRef) =>
+    projectDelivery(db, { ...input, from: "steer", to: "queue" }),
+)
+
 export const settleCompaction = Effect.fn("SessionPending.settleCompaction")(function* (
   db: DatabaseService,
   input: { readonly sessionID: SessionSchema.ID },
@@ -389,6 +436,39 @@ export const equivalent = (
   return false
 }
 
+const publishMutation = <A, E, R>(input: PendingRef, effect: Effect.Effect<A, E, R>) =>
+  inboxLocks.withLock(input.sessionID)(effect).pipe(Effect.asVoid)
+
+export const cancel = Effect.fn("SessionPending.cancel")((bus: Bus.Interface, input: PendingRef) =>
+  publishMutation(
+    input,
+    bus.publish(SessionEvent.InputCancelled, {
+      sessionID: input.sessionID,
+      inputID: input.id,
+    }),
+  ),
+)
+
+export const steer = Effect.fn("SessionPending.steer")((bus: Bus.Interface, input: PendingRef) =>
+  publishMutation(
+    input,
+    bus.publish(SessionEvent.InputSteered, {
+      sessionID: input.sessionID,
+      inputID: input.id,
+    }),
+  ),
+)
+
+export const queue = Effect.fn("SessionPending.queue")((bus: Bus.Interface, input: PendingRef) =>
+  publishMutation(
+    input,
+    bus.publish(SessionEvent.InputQueued, {
+      sessionID: input.sessionID,
+      inputID: input.id,
+    }),
+  ),
+)
+
 const publish = Effect.fn("SessionPending.publish")(function* (
   db: DatabaseService,
   bus: Bus.Interface,

packages/core/src/session/projector.ts

@@ -485,6 +485,24 @@ const layer = Layer.effectDiscard(
           .pipe(Effect.orDie)
       }),
     )
+    yield* bus.project(SessionEvent.InputCancelled, (event) =>
+      SessionPending.projectCancelled(db, {
+        id: event.data.inputID,
+        sessionID: event.data.sessionID,
+      }),
+    )
+    yield* bus.project(SessionEvent.InputSteered, (event) =>
+      SessionPending.projectSteered(db, {
+        id: event.data.inputID,
+        sessionID: event.data.sessionID,
+      }),
+    )
+    yield* bus.project(SessionEvent.InputQueued, (event) =>
+      SessionPending.projectQueued(db, {
+        id: event.data.inputID,
+        sessionID: event.data.sessionID,
+      }),
+    )
     yield* bus.project(SessionEvent.Compaction.Admitted, (event) =>
       Effect.gen(function* () {
         if (event.durable === undefined)

packages/core/src/shell.ts

@@ -6,9 +6,9 @@ import { ChildProcess } from "effect/unstable/process"
 import { produce } from "immer"
 import { Shell } from "@opencode-ai/schema/shell"
 import { makeLocationNode } from "@opencode-ai/util/effect/app-node"
-import { AppProcess } from "@opencode-ai/util/process"
 import { Config } from "./config"
 import { Bus } from "./bus"
+import { Environment } from "./environment"
 import { Location } from "./location"
 import { Global } from "@opencode-ai/util/global"
 import { ShellSelect } from "./shell/select"
@@ -65,285 +65,284 @@ export interface Interface {
 
 export class Service extends Context.Service<Service, Interface>()("@opencode/Shell") {}
 
-export const layer = (options?: ShellSelect.Options) => Layer.effect(
-  Service,
-  Effect.gen(function* () {
-    const bus = yield* Bus.Service
-    const location = yield* Location.Service
-    const config = yield* Config.Service
-    const global = yield* Global.Service
-    const appProcess = yield* AppProcess.Service
-    const hooks = yield* PluginHooks.Service
-    const context = yield* Effect.context()
-    const runFork = Effect.runForkWith(context)
-    const sessions = new Map<string, Active>()
-    const exitOrder: string[] = []
+export const layer = (options?: ShellSelect.Options) =>
+  Layer.effect(
+    Service,
+    Effect.gen(function* () {
+      const bus = yield* Bus.Service
+      const location = yield* Location.Service
+      const config = yield* Config.Service
+      const global = yield* Global.Service
+      const environment = yield* Environment.Service
+      const hooks = yield* PluginHooks.Service
+      const context = yield* Effect.context()
+      const runFork = Effect.runForkWith(context)
+      const sessions = new Map<string, Active>()
+      const exitOrder: string[] = []
 
-    const outputDir = path.join(global.data, "shell", location.project.id)
-    const { mkdir, unlink } = yield* Effect.promise(() => import("fs/promises"))
-    const { createWriteStream, createReadStream } = yield* Effect.promise(() => import("fs"))
-    yield* Effect.promise(() => mkdir(outputDir, { recursive: true }))
+      const outputDir = path.join(global.data, "shell", location.project.id)
+      const { mkdir, unlink } = yield* Effect.promise(() => import("fs/promises"))
+      const { createWriteStream, createReadStream } = yield* Effect.promise(() => import("fs"))
+      yield* Effect.promise(() => mkdir(outputDir, { recursive: true }))
 
-    yield* Effect.addFinalizer(() =>
-      Effect.gen(function* () {
-        for (const session of sessions.values()) {
-          if (session.timeoutFiber) yield* Fiber.interrupt(session.timeoutFiber)
-          // Unblock waiters still pending at teardown; succeed is a no-op once already resolved.
-          yield* Deferred.fail(session.done, new NotFoundError({ id: Shell.ID.make(session.info.id) }))
+      yield* Effect.addFinalizer(() =>
+        Effect.gen(function* () {
+          for (const session of sessions.values()) {
+            if (session.timeoutFiber) yield* Fiber.interrupt(session.timeoutFiber)
+            // Unblock waiters still pending at teardown; succeed is a no-op once already resolved.
+            yield* Deferred.fail(session.done, new NotFoundError({ id: Shell.ID.make(session.info.id) }))
+          }
+          sessions.clear()
+          exitOrder.length = 0
+        }),
+      )
+
+      const require = Effect.fn("Shell.require")(function* (id: Shell.ID) {
+        const session = sessions.get(id)
+        if (!session) return yield* new NotFoundError({ id })
+        return session
+      })
+
+      const removeSession = Effect.fnUntraced(function* (id: Shell.ID) {
+        const session = sessions.get(id)
+        if (!session) return
+        sessions.delete(id)
+        const index = exitOrder.indexOf(id)
+        if (index !== -1) exitOrder.splice(index, 1)
+        if (session.timeoutFiber) yield* Fiber.interrupt(session.timeoutFiber)
+        // Unblock any wait still pending when the command is removed before it terminated.
+        yield* Deferred.fail(session.done, new NotFoundError({ id }))
+        yield* Effect.promise(() => unlink(session.file).catch(() => {}))
+        yield* bus.publish(Shell.Event.Deleted, { id })
+      })
+
+      const remove = Effect.fn("Shell.remove")(function* (id: Shell.ID) {
+        yield* require(id)
+        yield* removeSession(id)
+      })
+
+      const list = Effect.fn("Shell.list")(function* () {
+        return Array.from(sessions.values())
+          .filter((session) => session.info.status === "running")
+          .map((session) => session.info)
+      })
+
+      const get = Effect.fn("Shell.get")(function* (id: Shell.ID) {
+        return (yield* require(id)).info
+      })
+
+      const wait = Effect.fn("Shell.wait")(function* (id: Shell.ID) {
+        return yield* Deferred.await((yield* require(id)).done)
+      })
+
+      const timeout = Effect.fn("Shell.timeout")(function* (id: Shell.ID, duration: number) {
+        const session = yield* require(id)
+        if (session.info.status !== "running" || !session.timeout) return session.info
+        yield* session.timeout(duration)
+        return session.info
+      })
+
+      const resolve = () =>
+        config.entries().pipe(Effect.map((entries) => ShellSelect.preferred(Config.latest(entries, "shell"), options)))
+
+      const name = () => resolve().pipe(Effect.map(ShellSelect.name))
+
+      const output = Effect.fn("Shell.output")(function* (id: Shell.ID, input?: Shell.OutputInput) {
+        const session = yield* require(id)
+        const cursor = input?.cursor ?? 0
+        const limit = input?.limit ?? 65536
+        if (cursor >= session.size) return { output: "", cursor: session.size, size: session.size, truncated: false }
+        const start = Math.max(0, cursor)
+        const length = Math.min(limit, session.size - start)
+        const buffer = Buffer.alloc(length)
+        const bytesRead = yield* Effect.promise(
+          () =>
+            new Promise<number>((resolve) => {
+              const stream = createReadStream(session.file, { start, end: start + length - 1 })
+              let offset = 0
+              stream.on("data", (chunk: string | Buffer) => {
+                const bytes = Buffer.from(chunk)
+                bytes.copy(buffer, offset)
+                offset += bytes.length
+              })
+              stream.on("end", () => resolve(offset))
+              stream.on("error", () => resolve(0))
+            }),
+        )
+        return {
+          output: buffer.subarray(0, bytesRead).toString("utf8"),
+          cursor: start + bytesRead,
+          size: session.size,
+          truncated: false,
         }
-        sessions.clear()
-        exitOrder.length = 0
-      }),
-    )
+      })
 
-    const require = Effect.fn("Shell.require")(function* (id: Shell.ID) {
-      const session = sessions.get(id)
-      if (!session) return yield* new NotFoundError({ id })
-      return session
-    })
+      const create = Effect.fn("Shell.create")(function* <E = never, R = never>(
+        input: Shell.CreateInput,
+        before?: (input: ShellCreateBefore) => Effect.Effect<void, E, R>,
+      ) {
+        const invocation: ShellCreateBefore = {
+          command: input.command,
+          cwd: input.cwd ?? location.directory,
+          timeout: input.timeout,
+          shell: yield* resolve(),
+          env: {
+            ...process.env,
+            TERM: "xterm-256color",
+            OPENCODE_TERMINAL: "1",
+          },
+        }
+        yield* hooks.trigger("shell", "create.before", invocation)
+        if (before) yield* before(invocation)
 
-    const removeSession = Effect.fnUntraced(function* (id: Shell.ID) {
-      const session = sessions.get(id)
-      if (!session) return
-      sessions.delete(id)
-      const index = exitOrder.indexOf(id)
-      if (index !== -1) exitOrder.splice(index, 1)
-      if (session.timeoutFiber) yield* Fiber.interrupt(session.timeoutFiber)
-      // Unblock any wait still pending when the command is removed before it terminated.
-      yield* Deferred.fail(session.done, new NotFoundError({ id }))
-      yield* Effect.promise(() => unlink(session.file).catch(() => {}))
-      yield* bus.publish(Shell.Event.Deleted, { id })
-    })
+        const id = Shell.ID.ascending()
+        const args = ShellSelect.args(invocation.shell, invocation.command)
+        const file = path.join(outputDir, `${id}.out`)
 
-    const remove = Effect.fn("Shell.remove")(function* (id: Shell.ID) {
-      yield* require(id)
-      yield* removeSession(id)
-    })
+        const info: Info = {
+          id,
+          status: "running",
+          command: invocation.command,
+          cwd: invocation.cwd,
+          shell: invocation.shell,
+          file,
+          metadata: input.metadata ?? {},
+          time: { started: Date.now() },
+        }
 
-    const list = Effect.fn("Shell.list")(function* () {
-      return Array.from(sessions.values())
-        .filter((session) => session.info.status === "running")
-        .map((session) => session.info)
-    })
-
-    const get = Effect.fn("Shell.get")(function* (id: Shell.ID) {
-      return (yield* require(id)).info
-    })
-
-    const wait = Effect.fn("Shell.wait")(function* (id: Shell.ID) {
-      return yield* Deferred.await((yield* require(id)).done)
-    })
-
-    const timeout = Effect.fn("Shell.timeout")(function* (id: Shell.ID, duration: number) {
-      const session = yield* require(id)
-      if (session.info.status !== "running" || !session.timeout) return session.info
-      yield* session.timeout(duration)
-      return session.info
-    })
-
-    const resolve = () =>
-      config
-        .entries()
-        .pipe(Effect.map((entries) => ShellSelect.preferred(Config.latest(entries, "shell"), options)))
-
-    const name = () => resolve().pipe(Effect.map(ShellSelect.name))
-
-    const output = Effect.fn("Shell.output")(function* (id: Shell.ID, input?: Shell.OutputInput) {
-      const session = yield* require(id)
-      const cursor = input?.cursor ?? 0
-      const limit = input?.limit ?? 65536
-      if (cursor >= session.size) return { output: "", cursor: session.size, size: session.size, truncated: false }
-      const start = Math.max(0, cursor)
-      const length = Math.min(limit, session.size - start)
-      const buffer = Buffer.alloc(length)
-      const bytesRead = yield* Effect.promise(
-        () =>
-          new Promise<number>((resolve) => {
-            const stream = createReadStream(session.file, { start, end: start + length - 1 })
-            let offset = 0
-            stream.on("data", (chunk: string | Buffer) => {
-              const bytes = Buffer.from(chunk)
-              bytes.copy(buffer, offset)
-              offset += bytes.length
-            })
-            stream.on("end", () => resolve(offset))
-            stream.on("error", () => resolve(0))
-          }),
-      )
-      return {
-        output: buffer.subarray(0, bytesRead).toString("utf8"),
-        cursor: start + bytesRead,
-        size: session.size,
-        truncated: false,
-      }
-    })
-
-    const create = Effect.fn("Shell.create")(function* <E = never, R = never>(
-      input: Shell.CreateInput,
-      before?: (input: ShellCreateBefore) => Effect.Effect<void, E, R>,
-    ) {
-      const invocation: ShellCreateBefore = {
-        command: input.command,
-        cwd: input.cwd ?? location.directory,
-        timeout: input.timeout,
-        shell: yield* resolve(),
-        env: {
-          ...process.env,
-          TERM: "xterm-256color",
-          OPENCODE_TERMINAL: "1",
-        },
-      }
-      yield* hooks.trigger("shell", "create.before", invocation)
-      if (before) yield* before(invocation)
-
-      const id = Shell.ID.ascending()
-      const args = ShellSelect.args(invocation.shell, invocation.command)
-      const file = path.join(outputDir, `${id}.out`)
-
-      const info: Info = {
-        id,
-        status: "running",
-        command: invocation.command,
-        cwd: invocation.cwd,
-        shell: invocation.shell,
-        file,
-        metadata: input.metadata ?? {},
-        time: { started: Date.now() },
-      }
-
-      // Spawn via AppProcess and stream combined output to the file. The handle is scope-bound, so
-      // the managing fiber keeps its scope open until the command terminates (it awaits `done` at the
-      // end). `create` returns once `ready` resolves with the registered session.
-      const ready = Deferred.makeUnsafe<Active>()
-      runFork(
-        Effect.scoped(
-          Effect.gen(function* () {
-            const handle = yield* appProcess.spawn(
-              ChildProcess.make(invocation.shell, args, {
-                cwd: invocation.cwd,
-                env: invocation.env,
-                stdin: "ignore",
-                detached: process.platform !== "win32",
-                forceKillAfter: Duration.seconds(3),
-              }),
-            )
-            const session: Active = {
-              info: produce(info, (draft) => {
-                draft.pid = handle.pid
-              }),
-              file,
-              size: 0,
-              done: Deferred.makeUnsafe<Info, NotFoundError>(),
-            }
-            sessions.set(id, session)
-
-            const stream = createWriteStream(file)
-            const outputDone = Deferred.makeUnsafe<void>()
-            const pump = handle.all.pipe(
-              Stream.runForEach((chunk: Uint8Array) =>
-                Effect.sync(() => {
-                  stream.write(chunk)
-                  session.size += chunk.length
+        // Spawn through the Environment and stream combined output to the file. The handle is scope-bound, so
+        // the managing fiber keeps its scope open until the command terminates (it awaits `done` at the
+        // end). `create` returns once `ready` resolves with the registered session.
+        const ready = Deferred.makeUnsafe<Active>()
+        runFork(
+          Effect.scoped(
+            Effect.gen(function* () {
+              const handle = yield* environment.spawner.spawn(
+                ChildProcess.make(invocation.shell, args, {
+                  cwd: invocation.cwd,
+                  env: invocation.env,
+                  stdin: "ignore",
+                  detached: process.platform !== "win32",
+                  forceKillAfter: Duration.seconds(3),
                 }),
-              ),
-            )
-            runFork(
-              Effect.gen(function* () {
-                yield* pump.pipe(Effect.catch(() => Effect.void))
-                yield* Effect.promise(
-                  () =>
-                    new Promise<void>((resolve) => {
-                      stream.end(() => resolve())
-                    }),
-                )
-                yield* Deferred.succeed(outputDone, undefined)
-              }).pipe(Effect.catch(() => Deferred.succeed(outputDone, undefined))),
-            )
-            yield* Effect.promise(
-              () =>
-                new Promise<void>((resolve) => {
-                  stream.once("open", () => resolve())
-                  stream.once("error", () => resolve())
+              )
+              const session: Active = {
+                info: produce(info, (draft) => {
+                  draft.pid = handle.pid
                 }),
-            )
+                file,
+                size: 0,
+                done: Deferred.makeUnsafe<Info, NotFoundError>(),
+              }
+              sessions.set(id, session)
 
-            const finish = (status: Info["status"], exit?: number, beforeWait = Effect.void) =>
-              Effect.gen(function* () {
-                if (session.info.status !== "running") return
-                session.info = produce(session.info, (draft) => {
-                  draft.status = status
-                  if (exit !== undefined) draft.exit = exit
-                  draft.time.completed = Date.now()
-                })
-                yield* beforeWait
-                yield* Deferred.await(outputDone)
-                // Resolve waiters with the terminal Info before any retention eviction, so an evicted
-                // session still reports success rather than the removal NotFoundError. This runs before
-                // the timeout-fiber interrupt below, which on the timeout path would otherwise cancel
-                // this very fiber (finish is invoked by the timeout fiber) before waiters are resolved.
-                yield* Deferred.succeed(session.done, session.info)
-                yield* bus.publish(Shell.Event.Exited, {
-                  id,
-                  ...(exit !== undefined ? { exit } : {}),
-                  status,
-                })
-                exitOrder.push(id)
-                while (exitOrder.length > EXITED_LIMIT) {
-                  const oldest = exitOrder[0]
-                  if (!oldest) break
-                  yield* removeSession(Shell.ID.make(oldest))
-                }
-                // Cancel a pending timeout once the command exits on its own. Interrupting last avoids
-                // aborting finish when finish itself runs on the timeout fiber.
-                if (session.timeoutFiber) yield* Fiber.interrupt(session.timeoutFiber)
-              })
+              const stream = createWriteStream(file)
+              const outputDone = Deferred.makeUnsafe<void>()
+              const pump = handle.all.pipe(
+                Stream.runForEach((chunk: Uint8Array) =>
+                  Effect.sync(() => {
+                    stream.write(chunk)
+                    session.size += chunk.length
+                  }),
+                ),
+              )
+              runFork(
+                Effect.gen(function* () {
+                  yield* pump.pipe(Effect.catch(() => Effect.void))
+                  yield* Effect.promise(
+                    () =>
+                      new Promise<void>((resolve) => {
+                        stream.end(() => resolve())
+                      }),
+                  )
+                  yield* Deferred.succeed(outputDone, undefined)
+                }).pipe(Effect.catch(() => Deferred.succeed(outputDone, undefined))),
+              )
+              yield* Effect.promise(
+                () =>
+                  new Promise<void>((resolve) => {
+                    stream.once("open", () => resolve())
+                    stream.once("error", () => resolve())
+                  }),
+              )
 
-            session.timeout = (duration) =>
-              Effect.gen(function* () {
-                if (session.timeoutFiber) yield* Fiber.interrupt(session.timeoutFiber)
-                session.timeoutFiber = undefined
-                if (duration === 0 || session.info.status !== "running") return
-                session.timeoutFiber = runFork(
-                  Effect.sleep(Duration.millis(duration)).pipe(
-                    Effect.flatMap(() =>
-                      finish("timeout", undefined, handle.kill().pipe(Effect.catch(() => Effect.void))),
+              const finish = (status: Info["status"], exit?: number, beforeWait = Effect.void) =>
+                Effect.gen(function* () {
+                  if (session.info.status !== "running") return
+                  session.info = produce(session.info, (draft) => {
+                    draft.status = status
+                    if (exit !== undefined) draft.exit = exit
+                    draft.time.completed = Date.now()
+                  })
+                  yield* beforeWait
+                  yield* Deferred.await(outputDone)
+                  // Resolve waiters with the terminal Info before any retention eviction, so an evicted
+                  // session still reports success rather than the removal NotFoundError. This runs before
+                  // the timeout-fiber interrupt below, which on the timeout path would otherwise cancel
+                  // this very fiber (finish is invoked by the timeout fiber) before waiters are resolved.
+                  yield* Deferred.succeed(session.done, session.info)
+                  yield* bus.publish(Shell.Event.Exited, {
+                    id,
+                    ...(exit !== undefined ? { exit } : {}),
+                    status,
+                  })
+                  exitOrder.push(id)
+                  while (exitOrder.length > EXITED_LIMIT) {
+                    const oldest = exitOrder[0]
+                    if (!oldest) break
+                    yield* removeSession(Shell.ID.make(oldest))
+                  }
+                  // Cancel a pending timeout once the command exits on its own. Interrupting last avoids
+                  // aborting finish when finish itself runs on the timeout fiber.
+                  if (session.timeoutFiber) yield* Fiber.interrupt(session.timeoutFiber)
+                })
+
+              session.timeout = (duration) =>
+                Effect.gen(function* () {
+                  if (session.timeoutFiber) yield* Fiber.interrupt(session.timeoutFiber)
+                  session.timeoutFiber = undefined
+                  if (duration === 0 || session.info.status !== "running") return
+                  session.timeoutFiber = runFork(
+                    Effect.sleep(Duration.millis(duration)).pipe(
+                      Effect.flatMap(() =>
+                        finish("timeout", undefined, handle.kill().pipe(Effect.catch(() => Effect.void))),
+                      ),
+                      Effect.catch(() => Effect.void),
                     ),
-                    Effect.catch(() => Effect.void),
-                  ),
-                )
-              })
+                  )
+                })
 
-            yield* session.timeout(invocation.timeout)
+              yield* session.timeout(invocation.timeout)
 
-            runFork(
-              handle.exitCode.pipe(
-                Effect.flatMap((code) => finish("exited", code)),
-                Effect.catch(() => Effect.void),
-              ),
-            )
+              runFork(
+                handle.exitCode.pipe(
+                  Effect.flatMap((code) => finish("exited", code)),
+                  Effect.catch(() => Effect.void),
+                ),
+              )
 
-            yield* bus.publish(Shell.Event.Created, { info })
-            yield* Deferred.succeed(ready, session)
-            // Hold the handle's scope open until the command terminates; closing it earlier would
-            // release (kill) the process before its exit is observed.
-            yield* Deferred.await(session.done).pipe(Effect.catch(() => Effect.void))
-          }),
-        ).pipe(Effect.catch(() => Effect.void)),
-      )
+              yield* bus.publish(Shell.Event.Created, { info })
+              yield* Deferred.succeed(ready, session)
+              // Hold the handle's scope open until the command terminates; closing it earlier would
+              // release (kill) the process before its exit is observed.
+              yield* Deferred.await(session.done).pipe(Effect.catch(() => Effect.void))
+            }),
+          ).pipe(Effect.catch(() => Effect.void)),
+        )
 
-      const session = yield* Deferred.await(ready)
-      return session.info
-    })
+        const session = yield* Deferred.await(ready)
+        return session.info
+      })
 
-    return Service.of({ name, create, list, get, wait, timeout, output, remove })
-  }),
-)
+      return Service.of({ name, create, list, get, wait, timeout, output, remove })
+    }),
+  )
 
 export function configured(options?: ShellSelect.Options) {
   return makeLocationNode({
     service: Service,
     layer: layer(options),
-    deps: [Bus.node, Location.node, Config.node, Global.node, AppProcess.node, PluginHooks.node],
+    deps: [Bus.node, Location.node, Config.node, Global.node, Environment.node, PluginHooks.node],
   })
 }
 

packages/core/src/skill.ts

@@ -2,8 +2,7 @@ export * as Skill from "./skill"
 
 import { makeLocationNode } from "@opencode-ai/util/effect/app-node"
 import path from "path"
-import { Context, Effect, Layer, Schema, Stream, Types } from "effect"
-import { FileSystem } from "@opencode-ai/schema/filesystem"
+import { Context, Effect, FiberMap, Layer, PubSub, Schema, Semaphore, Stream, Types } from "effect"
 import { Skill } from "@opencode-ai/schema/skill"
 import { Agent } from "./agent"
 import { ConfigMarkdown } from "./config/markdown"
@@ -13,6 +12,7 @@ import { Permission } from "./permission"
 import { AbsolutePath } from "./schema"
 import { SkillDiscovery } from "./skill/discovery"
 import { State } from "./state"
+import { Watcher } from "./filesystem/watcher"
 
 export const DirectorySource = Skill.DirectorySource
 export type DirectorySource = Skill.DirectorySource
@@ -81,6 +81,82 @@ const layer = Layer.effect(
     const discovery = yield* SkillDiscovery.Service
     const fs = yield* FSUtil.Service
     const bus = yield* Bus.Service
+    const watcher = yield* Watcher.Service
+    const cache = new Map<string, { skills: Info[]; paths: readonly string[] }>()
+    const watches = yield* FiberMap.make<string>()
+    const lock = Semaphore.makeUnsafe(1)
+    const changes = yield* PubSub.unbounded<string>()
+
+    const invalidate = Effect.fn("Skill.invalidateFromWatcher")(function* (file: string) {
+      const changed = yield* lock.withPermit(
+        Effect.gen(function* () {
+          const invalidated = Array.from(cache.entries()).filter(([, loaded]) =>
+            loaded.paths.some((item) => FSUtil.overlaps(item, file)),
+          )
+          if (invalidated.length === 0) return false
+          cache.clear()
+          yield* FiberMap.clear(watches)
+          yield* Effect.logInfo("skill cache invalidated", {
+            file,
+            sources: invalidated.map(([key]) => key),
+            skills: invalidated.flatMap(([, loaded]) => loaded.skills.map((skill) => skill.id)),
+          })
+          return true
+        }),
+      )
+      if (!changed) return
+      yield* bus.publish(Skill.Event.Updated, {}).pipe(Effect.asVoid)
+    })
+
+    yield* Stream.fromPubSub(changes).pipe(Stream.runForEach(invalidate), Effect.forkScoped({ startImmediately: true }))
+
+    const watch = Effect.fn("Skill.watch")(function* (directory: string, type: Watcher.WatchInput["type"]) {
+      const target = path.resolve(directory)
+      const updates = yield* watcher.subscribe(
+        type === "file" ? { path: target, type: "file" } : { path: target, type: "directory" },
+      )
+      yield* FiberMap.run(
+        watches,
+        `${type}:${target}`,
+        updates.pipe(Stream.runForEach((update) => PubSub.publish(changes, update.path).pipe(Effect.asVoid))),
+        {
+          onlyIfMissing: true,
+          startImmediately: true,
+        },
+      )
+    })
+
+    function firstMissing(target: string): Effect.Effect<string | undefined> {
+      const parent = path.dirname(target)
+      if (parent === target) return Effect.succeed(undefined)
+      return fs.isDir(parent).pipe(Effect.flatMap((exists) => (exists ? Effect.succeed(target) : firstMissing(parent))))
+    }
+
+    const watchDirectory: (directory: string) => Effect.Effect<string[]> = Effect.fn("Skill.watchDirectory")(function* (
+      directory: string,
+    ) {
+      const target = path.resolve(directory)
+      const resolved = yield* fs.realPath(directory).pipe(Effect.catch(() => Effect.succeed(undefined)))
+      if (resolved) {
+        yield* watch(resolved, "directory")
+        if (resolved !== target) {
+          yield* watch(target, "file")
+        }
+        return resolved === target ? [target] : [target, resolved]
+      }
+      const missing = yield* firstMissing(target)
+      if (missing) yield* watch(missing, "file")
+      if (
+        yield* fs.realPath(directory).pipe(
+          Effect.as(true),
+          Effect.catch(() => Effect.succeed(false)),
+        )
+      ) {
+        if (missing) yield* FiberMap.remove(watches, `file:${path.resolve(missing)}`)
+        return yield* watchDirectory(directory)
+      }
+      return [target]
+    })
 
     const state = State.create<Data, Draft>({
       name: "skill",
@@ -92,7 +168,10 @@ const layer = Layer.effect(
         },
         list: () => draft.sources as Source[],
       }),
-      finalize: () => bus.publish(Skill.Event.Updated, {}).pipe(Effect.asVoid),
+      finalize: () =>
+        lock
+          .withPermit(FiberMap.clear(watches).pipe(Effect.andThen(Effect.sync(() => cache.clear())), Effect.asVoid))
+          .pipe(Effect.andThen(bus.publish(Skill.Event.Updated, {})), Effect.asVoid),
     })
 
     const load = Effect.fn("Skill.load")(function* (source: Source) {
@@ -104,14 +183,22 @@ const layer = Layer.effect(
           directories: [],
           skills: [source.skill.id],
         })
-        return { skills: [source.skill], directories: [] }
+        return { skills: [source.skill], paths: [] }
       }
       const directories = source.type === "directory" ? [source.path] : yield* discovery.pull(source.url)
+      const roots = (yield* Effect.forEach(directories, watchDirectory)).flat()
+      const paths = [...roots]
       for (const directory of directories) {
         const files = yield* fs
           .scan("{*.md,**/SKILL.md}", { cwd: directory, absolute: true, include: "file", symlink: true, dot: true })
           .pipe(Effect.catch(() => Effect.succeed([] as string[])))
         for (const filepath of files.toSorted()) {
+          const resolved = yield* fs.realPath(filepath).pipe(Effect.catch(() => Effect.succeed(filepath)))
+          if (!roots.some((root) => FSUtil.contains(root, resolved))) {
+            const external = path.dirname(resolved)
+            paths.push(external)
+            yield* watch(external, "directory")
+          }
           const content = yield* fs.readFileStringSafe(filepath).pipe(Effect.catch(() => Effect.succeed(undefined)))
           if (!content) continue
           const markdown = ConfigMarkdown.parseOption(content)
@@ -139,38 +226,22 @@ const layer = Layer.effect(
         directories,
         skills: skills.map((skill) => skill.id),
       })
-      return { skills, directories }
+      return { skills, paths }
     })
 
-    const cache = new Map<string, { skills: Info[]; directories: readonly string[] }>()
-    const invalidate = Effect.fn("Skill.invalidateFromWatcher")(function* (file: string) {
-      const invalidated = Array.from(cache.entries()).filter(([, loaded]) =>
-        loaded.directories.some((directory) => FSUtil.contains(directory, file)),
-      )
-      if (invalidated.length === 0) return
-      for (const [key] of invalidated) cache.delete(key)
-      yield* Effect.logInfo("skill cache invalidated", {
-        file,
-        sources: invalidated.map(([key]) => key),
-        skills: invalidated.flatMap(([, loaded]) => loaded.skills.map((skill) => skill.id)),
-      })
-      yield* bus.publish(Skill.Event.Updated, {}).pipe(Effect.asVoid)
-    })
-
-    yield* bus.subscribe(FileSystem.Event.Changed).pipe(
-      Stream.runForEach((event) => invalidate(event.data.file)),
-      Effect.forkScoped({ startImmediately: true }),
-    )
-
     const list = Effect.fn("Skill.list")(function* () {
-      const skills = new Map<ID, Info>()
-      for (const source of state.get().sources) {
-        const key = Source.key(source)
-        const loaded = cache.get(key) ?? (yield* load(source))
-        cache.set(key, loaded)
-        for (const skill of loaded.skills) skills.set(skill.id, skill)
-      }
-      return Array.from(skills.values())
+      return yield* lock.withPermit(
+        Effect.gen(function* () {
+          const skills = new Map<ID, Info>()
+          for (const source of state.get().sources) {
+            const key = Source.key(source)
+            const loaded = cache.get(key) ?? (yield* load(source))
+            cache.set(key, loaded)
+            for (const skill of loaded.skills) skills.set(skill.id, skill)
+          }
+          return Array.from(skills.values())
+        }),
+      )
     })
 
     return Service.of({
@@ -187,5 +258,5 @@ const layer = Layer.effect(
 export const node = makeLocationNode({
   service: Service,
   layer,
-  deps: [SkillDiscovery.node, FSUtil.node, Bus.node],
+  deps: [SkillDiscovery.node, FSUtil.node, Bus.node, Watcher.node],
 })

packages/core/src/tool/plugin/edit.ts

@@ -11,9 +11,11 @@ import { ToolFailure } from "@opencode-ai/ai"
 import { FileDiff } from "@opencode-ai/schema/file-diff"
 import { Bom } from "@opencode-ai/util/bom"
 import { Effect, Schema } from "effect"
+import path from "path"
+import { Environment } from "../../environment"
 import { FileMutation } from "../../file-mutation"
 import { Formatter } from "../../formatter"
-import { FSUtil } from "@opencode-ai/util/fs-util"
+import { Location } from "../../location"
 import { LocationMutation } from "../../location-mutation"
 import { Permission } from "../../permission"
 import { fileDiff } from "./file-diff"
@@ -109,9 +111,10 @@ export const Plugin = {
   id: "opencode.tool.edit",
   effect: Effect.fn("EditTool.Plugin")(function* (ctx: PluginContext) {
     const mutation = yield* LocationMutation.Service
-    const files = yield* FileMutation.Service
+    const fileMutation = yield* FileMutation.Service
+    const environment = yield* Environment.Service
     const formatter = yield* Formatter.Service
-    const fs = yield* FSUtil.Service
+    const location = yield* Location.Service
     const permission = yield* Permission.Service
 
     yield* ctx.tool
@@ -152,17 +155,16 @@ export const Plugin = {
                 })
               }
 
-              const info = yield* fs
-                .stat(target.absolute)
-                .pipe(
-                  Effect.catchReason("PlatformError", "NotFound", () =>
-                    Effect.fail(new ToolFailure({ message: `File not found: ${input.path}` })),
-                  ),
-                )
-              if (info.type === "Directory") {
-                return yield* new ToolFailure({ message: `Path is a directory, not a file: ${input.path}` })
-              }
-              const original = yield* Bom.readFile(fs, target.absolute)
+              const original = yield* FileMutation.readText(environment.files, target.absolute).pipe(
+                Effect.catchTag("Environment.NotFound", () =>
+                  Effect.fail(new ToolFailure({ message: `File not found: ${input.path}` })),
+                ),
+                Effect.catchTag("Environment.WrongKind", (error) =>
+                  error.actual === "directory"
+                    ? Effect.fail(new ToolFailure({ message: `Path is a directory, not a file: ${input.path}` }))
+                    : Effect.fail(new ToolFailure({ message: `Unable to edit ${input.path}`, error })),
+                ),
+              )
               const source = original.text
               const ending = source.includes(crlf) ? crlf : "\n"
               const oldString = input.oldString.replaceAll(crlf, "\n").replaceAll("\n", ending)
@@ -204,19 +206,20 @@ export const Plugin = {
                 })
               }
               const replacementBom = replaced.startsWith("\uFEFF")
-              const result = yield* files.write({
+              const result = yield* fileMutation.write({
                 target,
                 content: Bom.join(replaced, original.bom || replacementBom),
               })
               const bom = original.bom || replacementBom
               const formatted = (yield* formatter.file(target.absolute))
-                ? yield* Bom.syncFile(fs, target.absolute, bom)
-                : (yield* Bom.readFile(fs, target.absolute)).text
+                ? yield* FileMutation.syncTextBom(environment.files, target.absolute, bom)
+                : (yield* FileMutation.readText(environment.files, target.absolute)).text
               return {
                 files: [fileDiff(result.resource, source, formatted)],
                 replacements,
               } satisfies Output
             }).pipe(
+              fileMutation.withLock([path.resolve(location.directory, input.path)]),
               Effect.map((output) => ({
                 output,
                 content: `Edited ${output.files[0]?.file} (${output.replacements} replacement${output.replacements === 1 ? "" : "s"})`,

packages/core/src/tool/plugin/glob.ts

@@ -4,8 +4,8 @@ import { ToolFailure } from "@opencode-ai/ai"
 import type { Context as PluginContext } from "@opencode-ai/plugin/effect/plugin"
 import { Effect, Schema } from "effect"
 import path from "path"
+import { Environment } from "../../environment"
 import { FileSystem } from "../../filesystem"
-import { FSUtil } from "@opencode-ai/util/fs-util"
 import { Location } from "../../location"
 import { LocationMutation } from "../../location-mutation"
 import { Ripgrep } from "../../ripgrep"
@@ -42,7 +42,7 @@ export const toModelContent = (entries: EncodedOutput, truncated = false) => {
 export const Plugin = {
   id: "opencode.tool.glob",
   effect: Effect.fn("GlobTool.Plugin")(function* (ctx: PluginContext) {
-    const fs = yield* FSUtil.Service
+    const environment = yield* Environment.Service
     const ripgrep = yield* Ripgrep.Service
     const location = yield* Location.Service
     const mutation = yield* LocationMutation.Service
@@ -82,22 +82,20 @@ export const Plugin = {
                 agent: context.agent,
                 source,
               })
-              const info = yield* fs
-                .stat(target.absolute)
-                .pipe(
-                  Effect.catchReason("PlatformError", "NotFound", () =>
-                    Effect.fail(new ToolFailure({ message: `Search path does not exist: ${searchPath ?? "."}` })),
-                  ),
-                )
-              if (info.type !== "Directory")
+              const type = yield* Environment.typeFollowing(environment.files, target.absolute).pipe(
+                Effect.catchTag("Environment.NotFound", () =>
+                  Effect.fail(new ToolFailure({ message: `Search path does not exist: ${searchPath ?? "."}` })),
+                ),
+              )
+              if (type !== "directory")
                 return yield* Effect.fail(
                   new ToolFailure({ message: `Search path is not a directory: ${searchPath ?? "."}` }),
                 )
-              const root = path.resolve(location.directory, searchPath ?? ".")
+              const root = target.absolute
               const limit = input.limit ?? FileSystem.DEFAULT_SEARCH_LIMIT
               const entries = yield* ripgrep
                 .glob({
-                  cwd: target.absolute,
+                  cwd: root,
                   pattern: input.pattern,
                   limit: limit + 1,
                 })

packages/core/src/tool/plugin/grep.ts

@@ -4,8 +4,8 @@ import type { Context as PluginContext } from "@opencode-ai/plugin/effect/plugin
 import { ToolFailure } from "@opencode-ai/ai"
 import { Effect, Schema } from "effect"
 import path from "path"
+import { Environment } from "../../environment"
 import { FileSystem } from "../../filesystem"
-import { FSUtil } from "@opencode-ai/util/fs-util"
 import { Location } from "../../location"
 import { LocationMutation } from "../../location-mutation"
 import { Permission } from "../../permission"
@@ -15,11 +15,11 @@ import { RelativePath } from "../../schema"
 export const name = "grep"
 
 export const Input = Schema.Struct({
-  pattern: FileSystem.GrepInput.fields.pattern.check(
-    Schema.isMinLength(1, { message: "Pattern must not be empty" }),
-  ).annotate({
-    description: "Regular expression to search for in file contents (ripgrep syntax)",
-  }),
+  pattern: FileSystem.GrepInput.fields.pattern
+    .check(Schema.isMinLength(1, { message: "Pattern must not be empty" }))
+    .annotate({
+      description: "Regular expression to search for in file contents (ripgrep syntax)",
+    }),
   path: Schema.optionalKey(RelativePath).annotate({
     description: "File or directory to search. Defaults to the current working directory.",
   }),
@@ -58,7 +58,7 @@ export const toModelContent = (matches: EncodedOutput, truncated = false) => {
 export const Plugin = {
   id: "opencode.tool.grep",
   effect: Effect.fn("GrepTool.Plugin")(function* (ctx: PluginContext) {
-    const fs = yield* FSUtil.Service
+    const environment = yield* Environment.Service
     const ripgrep = yield* Ripgrep.Service
     const location = yield* Location.Service
     const mutation = yield* LocationMutation.Service
@@ -66,104 +66,100 @@ export const Plugin = {
 
     yield* ctx.tool
       .transform((draft) =>
-        draft.add(
-          ({
-            name,
-            options: { codemode: false },
-            description:
-              "Search file contents using regular expressions. Use it to locate specific code, symbols, or text patterns, and narrow searches with `path` or `include`. Returns matching file paths, line numbers, and line previews.",
-            input: Input,
-            output: Output,
-            execute: (input, context) =>
-              Effect.gen(function* () {
-                const source = { type: "tool" as const, messageID: context.messageID, id: context.id }
-                const target = yield* mutation.resolve({ path: input.path ?? "." })
-                if (target.externalDirectory)
-                  yield* permission.assert({
-                    ...LocationMutation.externalDirectoryPermission(target.externalDirectory),
-                    sessionID: context.sessionID,
-                    agent: context.agent,
-                    source,
-                  })
+        draft.add({
+          name,
+          options: { codemode: false },
+          description:
+            "Search file contents using regular expressions. Use it to locate specific code, symbols, or text patterns, and narrow searches with `path` or `include`. Returns matching file paths, line numbers, and line previews.",
+          input: Input,
+          output: Output,
+          execute: (input, context) =>
+            Effect.gen(function* () {
+              const source = { type: "tool" as const, messageID: context.messageID, id: context.id }
+              const target = yield* mutation.resolve({ path: input.path ?? "." })
+              if (target.externalDirectory)
                 yield* permission.assert({
-                  action: name,
-                  resources: [input.pattern],
-                  save: ["*"],
-                  metadata: {
-                    root: ".",
-                    path: input.path,
-                    include: input.include,
-                    limit: input.limit,
-                  },
+                  ...LocationMutation.externalDirectoryPermission(target.externalDirectory),
                   sessionID: context.sessionID,
                   agent: context.agent,
                   source,
                 })
-                const root = path.resolve(location.directory, input.path ?? ".")
-                const info = yield* fs
-                  .stat(root)
-                  .pipe(
-                    Effect.catchReason("PlatformError", "NotFound", () =>
-                      Effect.fail(new ToolFailure({ message: `Search path does not exist: ${input.path ?? "."}` })),
-                    ),
-                  )
-                const cwd = info?.type === "Directory" ? root : path.dirname(root)
-                const limit = input.limit ?? FileSystem.DEFAULT_SEARCH_LIMIT
-                const matches = yield* ripgrep
-                  .grep({
-                    cwd,
-                    pattern: input.pattern,
-                    file: info?.type === "File" ? path.basename(root) : undefined,
-                    include: input.include,
-                    limit: limit + 1,
-                  })
-                  .pipe(
-                    Effect.timeoutOrElse({
-                      duration: FileSystem.DEFAULT_SEARCH_TIMEOUT_MS,
-                      orElse: () =>
-                        Effect.fail(
-                          new ToolFailure({
-                            message: `Search timed out after ${FileSystem.DEFAULT_SEARCH_TIMEOUT_MS / 1_000} seconds. Consider using a more specific path or pattern.`,
-                          }),
-                        ),
-                    }),
-                    Effect.map((result) =>
-                      result.map((match) =>
-                        FileSystem.Match.make({
-                          ...match,
-                          entry: FileSystem.Entry.make({
-                            ...match.entry,
-                            path: RelativePath.make(
-                              path.relative(location.directory, path.resolve(cwd, match.entry.path)),
-                            ),
-                          }),
+              yield* permission.assert({
+                action: name,
+                resources: [input.pattern],
+                save: ["*"],
+                metadata: {
+                  root: ".",
+                  path: input.path,
+                  include: input.include,
+                  limit: input.limit,
+                },
+                sessionID: context.sessionID,
+                agent: context.agent,
+                source,
+              })
+              const root = target.absolute
+              const type = yield* Environment.typeFollowing(environment.files, root).pipe(
+                Effect.catchTag("Environment.NotFound", () =>
+                  Effect.fail(new ToolFailure({ message: `Search path does not exist: ${input.path ?? "."}` })),
+                ),
+              )
+              const cwd = type === "directory" ? root : path.dirname(root)
+              const limit = input.limit ?? FileSystem.DEFAULT_SEARCH_LIMIT
+              const matches = yield* ripgrep
+                .grep({
+                  cwd,
+                  pattern: input.pattern,
+                  file: type === "file" ? path.basename(root) : undefined,
+                  include: input.include,
+                  limit: limit + 1,
+                })
+                .pipe(
+                  Effect.timeoutOrElse({
+                    duration: FileSystem.DEFAULT_SEARCH_TIMEOUT_MS,
+                    orElse: () =>
+                      Effect.fail(
+                        new ToolFailure({
+                          message: `Search timed out after ${FileSystem.DEFAULT_SEARCH_TIMEOUT_MS / 1_000} seconds. Consider using a more specific path or pattern.`,
                         }),
                       ),
+                  }),
+                  Effect.map((result) =>
+                    result.map((match) =>
+                      FileSystem.Match.make({
+                        ...match,
+                        entry: FileSystem.Entry.make({
+                          ...match.entry,
+                          path: RelativePath.make(
+                            path.relative(location.directory, path.resolve(cwd, match.entry.path)),
+                          ),
+                        }),
+                      }),
                     ),
-                  )
-                return { matches: matches.slice(0, limit), truncated: matches.length > limit }
-              }).pipe(
-                Effect.map((result) => ({
-                  output: result.matches,
-                  content: toModelContent(
-                    result.matches.map((match) => ({
-                      ...match,
-                      entry: { ...match.entry, path: path.resolve(location.directory, match.entry.path) },
-                    })),
-                    result.truncated,
                   ),
-                  metadata: { matches: result.matches.length, truncated: result.truncated },
-                })),
-                Effect.mapError((error) =>
-                  error instanceof ToolFailure
-                    ? error
-                    : error instanceof Ripgrep.InvalidPatternError
-                      ? new ToolFailure({ message: `Invalid regex pattern: ${error.message}` })
-                    : new ToolFailure({ message: `Unable to grep for ${input.pattern}`, error }),
+                )
+              return { matches: matches.slice(0, limit), truncated: matches.length > limit }
+            }).pipe(
+              Effect.map((result) => ({
+                output: result.matches,
+                content: toModelContent(
+                  result.matches.map((match) => ({
+                    ...match,
+                    entry: { ...match.entry, path: path.resolve(location.directory, match.entry.path) },
+                  })),
+                  result.truncated,
                 ),
+                metadata: { matches: result.matches.length, truncated: result.truncated },
+              })),
+              Effect.mapError((error) =>
+                error instanceof ToolFailure
+                  ? error
+                  : error instanceof Ripgrep.InvalidPatternError
+                    ? new ToolFailure({ message: `Invalid regex pattern: ${error.message}` })
+                    : new ToolFailure({ message: `Unable to grep for ${input.pattern}`, error }),
               ),
-          }),
-        ),
+            ),
+        }),
       )
       .pipe(Effect.orDie)
   }),

packages/core/src/tool/plugin/patch.ts

@@ -4,12 +4,13 @@ import type { Context as PluginContext } from "@opencode-ai/plugin/effect/plugin
 import { ToolFailure } from "@opencode-ai/ai"
 import { FileDiff } from "@opencode-ai/schema/file-diff"
 import { createTwoFilesPatch, diffLines } from "diff"
-import { Effect, Schema } from "effect"
-import { PlatformError } from "effect/PlatformError"
+import { Effect, Result, Schema } from "effect"
 import path from "path"
 import { Bom } from "@opencode-ai/util/bom"
 import { FSUtil } from "@opencode-ai/util/fs-util"
+import { Environment } from "../../environment"
 import { Formatter } from "../../formatter"
+import { FileMutation } from "../../file-mutation"
 import { Location } from "../../location"
 import { Patch } from "@opencode-ai/util/patch"
 import { Permission } from "../../permission"
@@ -44,7 +45,13 @@ export const toModelOutput = (output: Output) =>
   ].join("\n")
 
 type Prepared =
-  | (Extract<Patch.Hunk, { readonly type: "add" | "delete" }> & {
+  | (Extract<Patch.Hunk, { readonly type: "add" }> & {
+      readonly target: Target
+      readonly content: string
+      readonly before: string
+      readonly after: string
+    })
+  | (Extract<Patch.Hunk, { readonly type: "delete" }> & {
       readonly target: Target
       readonly before: string
       readonly after: string
@@ -69,7 +76,8 @@ interface Target {
 export const Plugin = {
   id: "opencode.tool.patch",
   effect: Effect.fn("PatchTool.Plugin")(function* (ctx: PluginContext) {
-    const fs = yield* FSUtil.Service
+    const environment = yield* Environment.Service
+    const mutation = yield* FileMutation.Service
     const formatter = yield* Formatter.Service
     const location = yield* Location.Service
     const permission = yield* Permission.Service
@@ -84,6 +92,13 @@ export const Plugin = {
           output: Output,
           execute: (input, context) => {
             const applied: Array<typeof Applied.Type> = []
+            const parsed = Patch.parse(input.patchText)
+            const lockTargets = Result.isSuccess(parsed)
+              ? parsed.success.flatMap((hunk) => [
+                  path.resolve(location.directory, hunk.path),
+                  ...(hunk.type === "update" && hunk.movePath ? [path.resolve(location.directory, hunk.movePath)] : []),
+                ])
+              : []
             const fail = (operation: string, error: unknown) => {
               const completed = applied.map((item) => item.resource).join(", ")
               return new ToolFailure({
@@ -97,7 +112,7 @@ export const Plugin = {
                 id: context.id,
               }
               if (!input.patchText) return yield* new ToolFailure({ message: "patchText is required" })
-              const hunks = yield* Effect.fromResult(Patch.parse(input.patchText)).pipe(
+              const hunks = yield* Effect.fromResult(parsed).pipe(
                 Effect.mapError((error) => new ToolFailure({ message: `patch verification failed: ${error.message}` })),
               )
               if (hunks.length === 0) {
@@ -125,18 +140,19 @@ export const Plugin = {
                     })
                   }
                   if (hunk.type === "add") {
+                    const content =
+                      hunk.contents.endsWith("\n") || hunk.contents === "" ? hunk.contents : `${hunk.contents}\n`
                     prepared.push({
                       ...hunk,
                       target,
+                      content,
                       before: "",
-                      after: Bom.split(
-                        hunk.contents.endsWith("\n") || hunk.contents === "" ? hunk.contents : `${hunk.contents}\n`,
-                      ).text,
+                      after: Bom.split(content).text,
                     })
                     return
                   }
                   if (hunk.type === "delete") {
-                    const content = yield* Bom.readFile(fs, target.absolute).pipe(
+                    const content = yield* FileMutation.readText(environment.files, target.absolute).pipe(
                       Effect.mapError(
                         (error) =>
                           new ToolFailure({
@@ -151,20 +167,7 @@ export const Plugin = {
                   const original =
                     previous ??
                     (yield* Effect.gen(function* () {
-                      const stats = yield* fs.stat(target.absolute).pipe(
-                        Effect.mapError(
-                          (error) =>
-                            new ToolFailure({
-                              message: `patch verification failed: Failed to read file to update ${target.absolute}: ${errorMessage(error)}`,
-                            }),
-                        ),
-                      )
-                      if (stats.type === "Directory") {
-                        return yield* new ToolFailure({
-                          message: `patch verification failed: Failed to read file to update ${target.absolute}: path is a directory`,
-                        })
-                      }
-                      const content = yield* Bom.readFile(fs, target.absolute).pipe(
+                      const content = yield* FileMutation.readText(environment.files, target.absolute).pipe(
                         Effect.mapError(
                           (error) =>
                             new ToolFailure({
@@ -233,13 +236,8 @@ export const Plugin = {
                 (change) =>
                   Effect.gen(function* () {
                     if (change.type === "add") {
-                      yield* fs
-                        .writeWithDirs(
-                          change.target.absolute,
-                          change.contents.endsWith("\n") || change.contents === ""
-                            ? change.contents
-                            : `${change.contents}\n`,
-                        )
+                      yield* environment.files
+                        .write(change.target.absolute, new TextEncoder().encode(change.content))
                         .pipe(Effect.mapError((error) => fail(`Failed to write ${change.target.resource}`, error)))
                       applied.push({
                         type: change.type,
@@ -249,7 +247,7 @@ export const Plugin = {
                       return
                     }
                     if (change.type === "delete") {
-                      yield* fs
+                      yield* environment.files
                         .remove(change.target.absolute)
                         .pipe(Effect.mapError((error) => fail(`Failed to delete ${change.target.resource}`, error)))
                       applied.push({
@@ -261,10 +259,10 @@ export const Plugin = {
                     }
                     if (change.moveTarget) {
                       const moveTarget = change.moveTarget
-                      yield* fs
-                        .writeWithDirs(moveTarget.absolute, change.content)
+                      yield* environment.files
+                        .write(moveTarget.absolute, new TextEncoder().encode(change.content))
                         .pipe(Effect.mapError((error) => fail(`Failed to write ${moveTarget.resource}`, error)))
-                      yield* fs
+                      yield* environment.files
                         .remove(change.target.absolute)
                         .pipe(
                           Effect.mapError((error) =>
@@ -278,8 +276,8 @@ export const Plugin = {
                       })
                       return
                     }
-                    yield* fs
-                      .writeWithDirs(change.target.absolute, change.content)
+                    yield* environment.files
+                      .write(change.target.absolute, new TextEncoder().encode(change.content))
                       .pipe(Effect.mapError((error) => fail(`Failed to write ${change.target.resource}`, error)))
                     applied.push({
                       type: change.type,
@@ -294,13 +292,13 @@ export const Plugin = {
                 [...new Set(applied.filter((item) => item.type !== "delete").map((item) => item.target))],
                 (target) =>
                   Effect.gen(function* () {
-                    const current = yield* Bom.readFile(fs, target).pipe(
+                    const current = yield* FileMutation.readText(environment.files, target).pipe(
                       Effect.mapError((error) => fail(`Failed to read ${target}`, error)),
                     )
                     formatted.set(
                       target,
                       (yield* formatter.file(target))
-                        ? yield* Bom.syncFile(fs, target, current.bom).pipe(
+                        ? yield* FileMutation.syncTextBom(environment.files, target, current.bom).pipe(
                             Effect.mapError((error) => fail(`Failed to sync ${target}`, error)),
                           )
                         : current.text,
@@ -315,6 +313,7 @@ export const Plugin = {
               })
               return { applied, files }
             }).pipe(
+              mutation.withLock(lockTargets),
               Effect.map((output) => ({
                 output,
                 content: toModelOutput(output),
@@ -345,10 +344,10 @@ export const Plugin = {
 }
 
 function errorMessage(error: unknown) {
-  if (error instanceof PlatformError) {
-    if (error.reason._tag === "NotFound") return "file does not exist"
-    return error.reason.description ?? error.reason.message
-  }
+  if (error instanceof Environment.NotFound) return "file does not exist"
+  if (error instanceof Environment.WrongKind)
+    return error.actual === "directory" ? "path is a directory" : `path is ${error.actual}`
+  if (error instanceof Environment.Failed) return errorMessage(error.cause)
   return error instanceof Error ? error.message : String(error)
 }
 

packages/core/src/tool/plugin/read.ts

@@ -11,6 +11,7 @@ import { Permission } from "../../permission"
 import { SessionInstructions } from "../../session/instructions"
 import { AbsolutePath } from "../../schema"
 import { ReadToolFileSystem } from "../read-filesystem"
+import { Environment } from "../../environment"
 
 export const name = "read"
 const FILENAME = "AGENTS.md"
@@ -72,16 +73,12 @@ export const Plugin = {
                 agent: context.agent,
                 source,
               })
-              const type = yield* reader
-                .inspect(absolute)
-                .pipe(Effect.catchReason("PlatformError", "NotFound", () => missing(input.path, target.absolute)))
-              const content =
-                type === "directory"
-                  ? yield* reader.list(absolute, { offset: input.offset, limit: input.limit })
-                  : yield* reader.read(absolute, resource, {
-                      offset: input.offset,
-                      limit: input.limit,
-                    })
+              const content = yield* reader.read(absolute, resource, { offset: input.offset, limit: input.limit }).pipe(
+                Effect.catchIf(
+                  (error) => error instanceof Environment.NotFound,
+                  () => missing(input.path, target.absolute),
+                ),
+              )
               // After a successful read, discover nearby AGENTS.md walking up to the Location
               // root exclusive and inject them as durable synthetic instructions. For a
               // directory listing the walk starts at the directory itself (so its own AGENTS.md
@@ -95,7 +92,7 @@ export const Plugin = {
                 // supplied by core initial instructions) is dropped by the dirname filter.
                 const discovered = yield* fs.up({
                   targets: [FILENAME],
-                  start: type === "directory" ? resolved : dirname(resolved),
+                  start: content.type === "list-page" ? resolved : dirname(resolved),
                   stop: root,
                 })
                 const candidates = (yield* Effect.forEach(discovered, fs.resolve)).filter(

packages/core/src/tool/plugin/shell.ts

@@ -5,8 +5,8 @@ import { ToolFailure } from "@opencode-ai/ai"
 import type { Content } from "@opencode-ai/schema/tool"
 import type { Context as PluginContext } from "@opencode-ai/plugin/effect/plugin"
 import { Deferred, Effect, Schema, Scope } from "effect"
-import { FSUtil } from "@opencode-ai/util/fs-util"
 import { Config } from "../../config"
+import { Environment } from "../../environment"
 import { LocationMutation } from "../../location-mutation"
 import { Permission } from "../../permission"
 import { PluginRuntime } from "../../plugin/runtime"
@@ -83,7 +83,7 @@ export const Plugin = {
   effect: Effect.fn("ShellTool.Plugin")(function* (ctx: PluginContext) {
     const runtime = yield* PluginRuntime.Service
     const scope = yield* Scope.Scope
-    const fsUtil = yield* FSUtil.Service
+    const environment = yield* Environment.Service
     const mutation = yield* LocationMutation.Service
     const shell = yield* Shell.Service
     const permission = yield* Permission.Service
@@ -179,14 +179,12 @@ export const Plugin = {
                         agent: context.agent,
                         source,
                       })
-                    const workdir = yield* fsUtil
-                      .stat(target.absolute)
-                      .pipe(
-                        Effect.catchReason("PlatformError", "NotFound", () =>
-                          Effect.fail(new Error(`Working directory does not exist: ${target.absolute}`)),
-                        ),
-                      )
-                    if (workdir.type !== "Directory")
+                    const workdir = yield* Environment.typeFollowing(environment.files, target.absolute).pipe(
+                      Effect.catchTag("Environment.NotFound", () =>
+                        Effect.fail(new Error(`Working directory does not exist: ${target.absolute}`)),
+                      ),
+                    )
+                    if (workdir !== "directory")
                       return yield* Effect.fail(new Error(`Working directory is not a directory: ${target.absolute}`))
                   }),
               )

packages/core/src/tool/plugin/write.ts

@@ -10,7 +10,7 @@ import type { Context as PluginContext } from "@opencode-ai/plugin/effect/plugin
 import { ToolFailure } from "@opencode-ai/ai"
 import { Effect, Schema } from "effect"
 import { Bom } from "@opencode-ai/util/bom"
-import { FSUtil } from "@opencode-ai/util/fs-util"
+import { Environment } from "../../environment"
 import { FileMutation } from "../../file-mutation"
 import { Formatter } from "../../formatter"
 import { LocationMutation } from "../../location-mutation"
@@ -47,9 +47,9 @@ export const Plugin = {
   id: "opencode.tool.write",
   effect: Effect.fn("WriteTool.Plugin")(function* (ctx: PluginContext) {
     const mutation = yield* LocationMutation.Service
-    const files = yield* FileMutation.Service
+    const fileMutation = yield* FileMutation.Service
+    const environment = yield* Environment.Service
     const formatter = yield* Formatter.Service
-    const fs = yield* FSUtil.Service
     const permission = yield* Permission.Service
 
     yield* ctx.tool
@@ -77,8 +77,8 @@ export const Plugin = {
                   agent: context.agent,
                   source,
                 })
-              const current = yield* Bom.readFile(fs, target.absolute).pipe(
-                Effect.catchReason("PlatformError", "NotFound", () => Effect.succeed(undefined)),
+              const current = yield* FileMutation.readText(environment.files, target.absolute).pipe(
+                Effect.catchTag("Environment.NotFound", () => Effect.succeed(undefined)),
               )
               const next = Bom.split(input.content)
               const preview = fileDiff(target.resource, current?.text ?? "", next.text, current ? "modified" : "added")
@@ -91,9 +91,11 @@ export const Plugin = {
                 agent: context.agent,
                 source,
               })
-              const result = yield* files.writeTextPreservingBom({ target, content: input.content })
-              const bom = (yield* Bom.readFile(fs, target.absolute)).bom
-              if (yield* formatter.file(target.absolute)) yield* Bom.syncFile(fs, target.absolute, bom)
+              const result = yield* fileMutation.writeTextPreservingBom({ target, content: input.content })
+              const bom = (yield* FileMutation.readText(environment.files, target.absolute)).bom
+              if (yield* formatter.file(target.absolute)) {
+                yield* FileMutation.syncTextBom(environment.files, target.absolute, bom)
+              }
               return result
             }).pipe(
               Effect.map((output) => ({ output, content: toModelOutput(output) })),

packages/core/src/tool/read-filesystem.ts

@@ -2,17 +2,22 @@ export * as ReadToolFileSystem from "./read-filesystem"
 
 import path from "path"
 import { pathToFileURL } from "url"
-import { Context, Effect, Layer, Option, Schema } from "effect"
-import { FileSystem } from "../filesystem"
-import { FSUtil } from "@opencode-ai/util/fs-util"
 import { makeLocationNode } from "@opencode-ai/util/effect/app-node"
+import { Context, Effect, Layer, Schema } from "effect"
+import { lookup } from "mime-types"
+import { Environment } from "../environment"
+import type { Files } from "../environment"
+import { FileSystem } from "../filesystem"
+import { Mime } from "../mime"
 import { AbsolutePath, NonNegativeInt, PositiveInt, RelativePath } from "../schema"
 
 export const MAX_READ_LINES = 2_000
 export const MAX_READ_BYTES = 50 * 1024
 export const MAX_MEDIA_INGEST_BYTES = 20 * 1024 * 1024
+const FIRST_CHUNK = 256 * 1024
 const MAX_LINE_LENGTH = 2_000
 const MAX_LINE_SUFFIX = `... (line truncated to ${MAX_LINE_LENGTH} chars)`
+const MEDIA_MIMES = new Set(["image/png", "image/jpeg", "image/gif", "image/webp", "application/pdf"])
 
 export class BinaryFileError extends Schema.TaggedErrorClass<BinaryFileError>()("ReadTool.BinaryFileError", {
   resource: Schema.String,
@@ -52,8 +57,13 @@ export class PathKindError extends Schema.TaggedErrorClass<PathKindError>()("Rea
   }
 }
 
-export type InspectError = FSUtil.Error | PathKindError
-export type ReadError = FSUtil.Error | BinaryFileError | MediaIngestLimitError | OffsetOutOfRangeError | PathKindError
+export type ReadError =
+  | Environment.NotFound
+  | Environment.Failed
+  | BinaryFileError
+  | MediaIngestLimitError
+  | OffsetOutOfRangeError
+  | PathKindError
 
 export const PageInput = Schema.Struct({
   offset: Schema.optionalKey(NonNegativeInt),
@@ -90,202 +100,113 @@ export class ListPage extends Schema.Class<ListPage>("ReadTool.ListPage")({
 }) {}
 
 export interface Interface {
-  readonly inspect: (path: AbsolutePath) => Effect.Effect<"file" | "directory", InspectError>
   readonly read: (
     path: AbsolutePath,
     resource: string,
     page?: PageInput,
-  ) => Effect.Effect<FileContent | TextPage, ReadError>
-  readonly list: (path: AbsolutePath, page?: PageInput) => Effect.Effect<ListPage, FSUtil.Error>
+  ) => Effect.Effect<FileContent | TextPage | ListPage, ReadError>
 }
 
 export class Service extends Context.Service<Service, Interface>()("@opencode/ReadToolFileSystem") {}
 
-const startsWith = (bytes: Uint8Array, prefix: number[]) => prefix.every((value, index) => bytes[index] === value)
-const mediaMime = (bytes: Uint8Array) => {
-  if (startsWith(bytes, [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a])) return "image/png"
-  if (startsWith(bytes, [0xff, 0xd8, 0xff])) return "image/jpeg"
-  if (startsWith(bytes, [0x47, 0x49, 0x46, 0x38])) return "image/gif"
-  if (startsWith(bytes, [0x52, 0x49, 0x46, 0x46]) && startsWith(bytes.subarray(8), [0x57, 0x45, 0x42, 0x50]))
-    return "image/webp"
-  if (startsWith(bytes, [0x25, 0x50, 0x44, 0x46, 0x2d])) return "application/pdf"
-}
-const binary = (bytes: Uint8Array) => {
-  if (bytes.length === 0) return false
-  let nonPrintable = 0
-  for (const byte of bytes) {
-    if (byte === 0) return true
-    if (byte < 9 || (byte > 13 && byte < 32)) nonPrintable++
-  }
-  return nonPrintable / bytes.length > 0.3
-}
-const decodeUtf8 = (decoder: TextDecoder, bytes?: Uint8Array) => decoder.decode(bytes, { stream: bytes !== undefined })
-const decodeChunk = (resource: string, decoder: TextDecoder, bytes: Uint8Array) =>
-  bytes.includes(0) ? Effect.fail(new BinaryFileError({ resource })) : Effect.succeed(decodeUtf8(decoder, bytes))
-
-export const inspect = Effect.fn("ReadTool.inspect")(function* (fs: FSUtil.Interface, input: string) {
-  const info = yield* fs.stat(input)
-  const type = info.type === "File" ? "file" : info.type === "Directory" ? "directory" : undefined
-  if (!type) return yield* Effect.fail(new PathKindError({ resource: input, expected: "a file or directory" }))
-  return type
-})
+const mimeType = (value: string) => lookup(value) || "application/octet-stream"
 
 export const read = Effect.fn("ReadTool.read")(function* (
-  fs: FSUtil.Interface,
-  input: string,
+  files: Files,
+  input: AbsolutePath,
   resource: string,
   page: PageInput = {},
 ) {
-  const real = yield* fs.realPath(input)
-  return yield* Effect.scoped(
-    Effect.gen(function* () {
-      const file = yield* fs.open(real, { flag: "r" })
-      const info = yield* file.stat
-      if (info.type !== "File") return yield* Effect.fail(new PathKindError({ resource, expected: "a file" }))
-      const first = Option.getOrElse(
-        yield* file.readAlloc(Math.min(64 * 1024, Number(info.size) || 4 * 1024)),
-        () => new Uint8Array(),
+  const first = yield* files.read(input, { offset: 0, length: FIRST_CHUNK }).pipe(
+    Effect.catchTag("Environment.WrongKind", (error) => {
+      if (error.actual !== "directory")
+        return Effect.fail(new PathKindError({ resource, expected: "a file or directory" }))
+      return files.list(input).pipe(
+        Effect.map((entries) => list(entries, page)),
+        Effect.catchTag("Environment.WrongKind", () =>
+          Effect.fail(new PathKindError({ resource, expected: "a file or directory" })),
+        ),
       )
-      const mime = mediaMime(first)
-      if (mime) {
-        if (info.size > MAX_MEDIA_INGEST_BYTES)
-          return yield* Effect.fail(new MediaIngestLimitError({ resource, maximumBytes: MAX_MEDIA_INGEST_BYTES }))
-        const chunks = [first]
-        let total = first.length
-        while (total <= MAX_MEDIA_INGEST_BYTES) {
-          const chunk = yield* file.readAlloc(Math.min(64 * 1024, MAX_MEDIA_INGEST_BYTES + 1 - total))
-          if (Option.isNone(chunk)) break
-          chunks.push(chunk.value)
-          total += chunk.value.length
-        }
-        if (total > MAX_MEDIA_INGEST_BYTES)
-          return yield* Effect.fail(new MediaIngestLimitError({ resource, maximumBytes: MAX_MEDIA_INGEST_BYTES }))
-        return {
-          type: "file" as const,
-          uri: pathToFileURL(real).href,
-          name: path.basename(real),
-          content: Buffer.concat(
-            chunks.map((chunk) => Buffer.from(chunk)),
-            total,
-          ).toString("base64"),
-          encoding: "base64" as const,
-          mime,
-        }
-      }
-      const paged = info.size > MAX_READ_BYTES || page.offset !== undefined || page.limit !== undefined
-      if (!paged) {
-        if (binary(first)) return yield* Effect.fail(new BinaryFileError({ resource }))
-        const decoder = new TextDecoder()
-        const text = [decodeUtf8(decoder, first)]
-        while (true) {
-          const chunk = yield* file.readAlloc(64 * 1024)
-          if (Option.isNone(chunk)) break
-          text.push(yield* decodeChunk(resource, decoder, chunk.value))
-        }
-        text.push(decodeUtf8(decoder))
-        return {
-          type: "file" as const,
-          uri: pathToFileURL(real).href,
-          name: path.basename(real),
-          content: text.join(""),
-          encoding: "utf8" as const,
-          mime: FSUtil.mimeType(real),
-        }
-      }
-      const offset = page.offset || 1
-      const limit = Math.min(page.limit || MAX_READ_LINES, MAX_READ_LINES)
-      const lines: string[] = []
-      const decoder = new TextDecoder()
-      let pending = ""
-      let discard = false
-      let line = 1
-      let bytes = 0
-      let next: number | undefined
-      const append = (input: string) => {
-        if (line < offset) {
-          line++
-          return true
-        }
-        if (lines.length >= limit || bytes >= MAX_READ_BYTES) {
-          next = line
-          return false
-        }
-        const text = input.length > MAX_LINE_LENGTH ? input.slice(0, MAX_LINE_LENGTH) + MAX_LINE_SUFFIX : input
-        const size = Buffer.byteLength(text, "utf-8") + (lines.length > 0 ? 1 : 0)
-        if (bytes + size > MAX_READ_BYTES) {
-          next = line
-          return false
-        }
-        lines.push(text)
-        bytes += size
-        line++
-        return true
-      }
-      const consume = (input: string) => {
-        let text = input
-        while (true) {
-          const index = text.indexOf("\n")
-          if (index === -1) {
-            if (!discard) {
-              pending += text
-              if (pending.length > MAX_LINE_LENGTH) {
-                pending = pending.slice(0, MAX_LINE_LENGTH + 1)
-                discard = true
-              }
-            }
-            break
-          }
-          const current = pending + (discard ? "" : text.slice(0, index))
-          pending = ""
-          discard = false
-          text = text.slice(index + 1)
-          if (!append(current.endsWith("\r") ? current.slice(0, -1) : current)) return false
-        }
-        return true
-      }
-      const consumeChunk = Effect.fnUntraced(function* (chunk: Uint8Array) {
-        let start = 0
-        while (start < chunk.length) {
-          if (lines.length >= limit || bytes >= MAX_READ_BYTES) {
-            next = line
-            return false
-          }
-          const newline = chunk.indexOf(10, start)
-          const end = newline === -1 ? chunk.length : newline + 1
-          const segment = chunk.subarray(start, end)
-          if (binary(segment)) return yield* Effect.fail(new BinaryFileError({ resource }))
-          if (!consume(decodeUtf8(decoder, segment))) return false
-          start = end
-        }
-        return true
-      })
-      let done = !(yield* consumeChunk(first))
-      while (!done) {
-        const chunk = yield* file.readAlloc(64 * 1024)
-        if (Option.isNone(chunk)) break
-        done = !(yield* consumeChunk(chunk.value))
-      }
-      if (!done) {
-        const tail = decodeUtf8(decoder)
-        if (!discard) pending += tail
-        if (pending) append(pending.endsWith("\r") ? pending.slice(0, -1) : pending)
-      }
-      if (lines.length === 0 && offset !== 1) return yield* Effect.fail(new OffsetOutOfRangeError({ offset }))
-      return new TextPage({
-        type: "text-page",
-        content: lines.join("\n"),
-        mime: FSUtil.mimeType(real),
-        offset,
-        truncated: next !== undefined,
-        ...(next === undefined ? {} : { next }),
-      })
     }),
   )
+  if (first instanceof ListPage) return first
+
+  const media = Mime.detect(first.bytes)
+  if (MEDIA_MIMES.has(media)) {
+    if (first.info.size > MAX_MEDIA_INGEST_BYTES)
+      return yield* new MediaIngestLimitError({ resource, maximumBytes: MAX_MEDIA_INGEST_BYTES })
+    const whole = yield* readFile(files, input, resource)
+    return {
+      type: "file" as const,
+      uri: pathToFileURL(input).href,
+      name: path.basename(input),
+      content: Buffer.from(whole.bytes).toString("base64"),
+      encoding: "base64" as const,
+      mime: media,
+    }
+  }
+
+  const paged = first.info.size > MAX_READ_BYTES || page.offset !== undefined || page.limit !== undefined
+  if (!paged) {
+    if (first.bytes.includes(0)) return yield* new BinaryFileError({ resource })
+    return {
+      type: "file" as const,
+      uri: pathToFileURL(input).href,
+      name: path.basename(input),
+      content: new TextDecoder().decode(first.bytes),
+      encoding: "utf8" as const,
+      mime: mimeType(input),
+    }
+  }
+
+  const chunks = [first.bytes]
+  while (true) {
+    const bytes = Buffer.concat(chunks)
+    const eof = bytes.length >= first.info.size
+    const result = textPage(bytes, eof, page)
+    if (result !== undefined) return yield* makeTextPage(bytes, input, resource, result)
+    const next = yield* readFile(files, input, resource, { offset: bytes.length, length: FIRST_CHUNK })
+    if (next.bytes.length === 0) {
+      const result = textPage(bytes, true, page)
+      if (result === undefined) return yield* Effect.die("Read page did not settle at EOF")
+      return yield* makeTextPage(bytes, input, resource, result)
+    }
+    chunks.push(next.bytes)
+  }
 })
 
-export const list = Effect.fn("ReadTool.list")(function* (fs: FSUtil.Interface, input: string, page: PageInput = {}) {
-  const real = yield* fs.realPath(input)
-  const items = yield* fs.readDirectoryEntries(real)
+const readFile = (
+  files: Files,
+  input: AbsolutePath,
+  resource: string,
+  range?: { readonly offset: number; readonly length: number },
+) =>
+  files
+    .read(input, range)
+    .pipe(
+      Effect.catchTag("Environment.WrongKind", () => Effect.fail(new PathKindError({ resource, expected: "a file" }))),
+    )
+
+const makeTextPage = Effect.fnUntraced(function* (
+  bytes: Uint8Array,
+  input: AbsolutePath,
+  resource: string,
+  result: NonNullable<ReturnType<typeof textPage>>,
+) {
+  if (bytes.subarray(0, result.consumed).includes(0)) return yield* new BinaryFileError({ resource })
+  if (result.entries.length === 0 && result.offset !== 1)
+    return yield* new OffsetOutOfRangeError({ offset: result.offset })
+  return new TextPage({
+    type: "text-page",
+    content: result.entries.join("\n"),
+    mime: mimeType(input),
+    offset: result.offset,
+    truncated: result.next !== undefined,
+    ...(result.next === undefined ? {} : { next: result.next }),
+  })
+})
+
+const list = (items: ReadonlyArray<Environment.DirEntry>, page: PageInput) => {
   const offset = page.offset || 1
   const limit = Math.min(page.limit || MAX_READ_LINES, MAX_READ_LINES)
   const visible = items
@@ -316,18 +237,58 @@ export const list = Effect.fn("ReadTool.list")(function* (fs: FSUtil.Interface,
     truncated,
     ...(truncated ? { next: offset + selected.length } : {}),
   })
-})
+}
+
+const textPage = (bytes: Uint8Array, eof: boolean, page: PageInput) => {
+  const offset = page.offset || 1
+  const limit = Math.min(page.limit || MAX_READ_LINES, MAX_READ_LINES)
+  const decoded = new TextDecoder().decode(bytes)
+  const split = decoded.split("\n")
+  const complete = eof ? (split.at(-1) === "" ? split.slice(0, -1) : split) : split.slice(0, -1)
+  const available = complete.map((line) => (line.endsWith("\r") ? line.slice(0, -1) : line))
+
+  const entries: string[] = []
+  let size = 0
+  let next: number | undefined
+  for (const [index, value] of available.slice(offset - 1).entries()) {
+    const line = offset + index
+    if (entries.length >= limit || size >= MAX_READ_BYTES) {
+      next = line
+      break
+    }
+    const text = value.length > MAX_LINE_LENGTH ? value.slice(0, MAX_LINE_LENGTH) + MAX_LINE_SUFFIX : value
+    const lineSize = Buffer.byteLength(text, "utf-8") + (entries.length > 0 ? 1 : 0)
+    if (size + lineSize > MAX_READ_BYTES) {
+      next = line
+      break
+    }
+    entries.push(text)
+    size += lineSize
+  }
+  if (next === undefined && entries.length >= limit && (!eof || offset - 1 + entries.length < available.length))
+    next = offset + entries.length
+  if (!eof && next === undefined) return
+
+  const consumedLines = next === undefined ? available.length : next - 1
+  const consumed = consumedLines === 0 ? 0 : (nthNewline(bytes, consumedLines) ?? bytes.length)
+  return { entries, offset, next, consumed }
+}
+
+const nthNewline = (bytes: Uint8Array, count: number) => {
+  let found = 0
+  for (const [index, byte] of bytes.entries()) {
+    if (byte !== 10) continue
+    found++
+    if (found === count) return index + 1
+  }
+}
 
 const layer = Layer.effect(
   Service,
   Effect.gen(function* () {
-    const fs = yield* FSUtil.Service
-    return Service.of({
-      inspect: (path) => inspect(fs, path),
-      read: (path, resource, page) => read(fs, path, resource, page),
-      list: (path, page) => list(fs, path, page),
-    })
+    const environment = yield* Environment.Service
+    return Service.of({ read: (path, resource, page) => read(environment.files, path, resource, page) })
   }),
 )
 
-export const node = makeLocationNode({ service: Service, layer, deps: [FSUtil.node] })
+export const node = makeLocationNode({ service: Service, layer, deps: [Environment.node] })

packages/core/test/config/provider.test.ts

@@ -50,6 +50,33 @@ function withEnv<A, E, R>(vars: Record<string, string | undefined>, effect: () =
 const decode = Schema.decodeUnknownSync(Info)
 
 describe("ConfigProviderPlugin.Plugin", () => {
+  it.effect("adds key auth for custom providers without env credentials", () =>
+    Effect.gen(function* () {
+      const integrations = yield* Integration.Service
+      const entries = [
+        new Document({
+          type: "document",
+          info: decode({
+            providers: {
+              litellm: {
+                package: "aisdk:@ai-sdk/openai-compatible",
+                models: { chat: {} },
+              },
+            },
+          }),
+        }),
+      ]
+
+      yield* addPlugin(entries)
+
+      expect(yield* integrations.get(Integration.ID.make("litellm"))).toMatchObject({
+        id: "litellm",
+        name: "litellm",
+        methods: [{ type: "key", label: "Manually enter API Key" }],
+      })
+    }),
+  )
+
   it.effect("defaults custom models to agent capabilities", () =>
     Effect.gen(function* () {
       const catalog = yield* Catalog.Service

packages/core/test/environment.test.ts

@@ -0,0 +1,88 @@
+import fs from "node:fs/promises"
+import { describe, expect } from "bun:test"
+import { Effect } from "effect"
+import { ChildProcessSpawner } from "effect/unstable/process"
+import { CrossSpawnSpawner } from "@opencode-ai/util/cross-spawn-spawner"
+import { LayerNode } from "@opencode-ai/util/effect/layer-node"
+import {
+  execDefaults,
+  Failed,
+  makeFiles,
+  makeLocalDriver,
+  makeMemoryDriver,
+  NotFound,
+  typeFollowing,
+} from "../src/environment/index"
+import { tmpdir } from "./fixture/tmpdir"
+import { environmentConformance } from "./lib/environment-conformance"
+import { it } from "./lib/effect"
+
+describe("typeFollowing", () => {
+  it.effect("follows symlinks without changing stat semantics", () =>
+    Effect.gen(function* () {
+      const driver = makeMemoryDriver()
+      const files = makeFiles(driver)
+      yield* files.mkdir("/directory")
+      yield* files.write("/file", new Uint8Array())
+      yield* driver.symlink("/directory", "/directory-link")
+      yield* driver.symlink("/file", "/file-link")
+      yield* driver.symlink("/missing", "/dangling-link")
+
+      expect(yield* typeFollowing(files, "/directory-link")).toBe("directory")
+      expect(yield* typeFollowing(files, "/file-link")).toBe("file")
+      expect(yield* typeFollowing(files, "/dangling-link").pipe(Effect.flip)).toBeInstanceOf(NotFound)
+    }),
+  )
+})
+
+environmentConformance("memory environment", () =>
+  Effect.sync(() => {
+    const driver = makeMemoryDriver()
+    return {
+      files: makeFiles(driver),
+      root: `/workspace-${crypto.randomUUID()}`,
+      symlink: driver.symlink,
+    }
+  }),
+)
+
+environmentConformance("local environment", () =>
+  Effect.gen(function* () {
+    const spawner = yield* ChildProcessSpawner.ChildProcessSpawner
+    const tmp = yield* Effect.promise(() => tmpdir("opencode-local-environment-"))
+    return {
+      files: makeFiles(makeLocalDriver(spawner)),
+      root: tmp.path,
+      ...(process.platform === "win32"
+        ? {}
+        : {
+            symlink: (target: string, link: string) =>
+              Effect.tryPromise({
+                try: () => fs.symlink(target, link),
+                catch: (cause) => new Failed({ path: link, cause }),
+              }),
+          }),
+      dispose: Effect.promise(() => tmp[Symbol.asyncDispose]()),
+    }
+  }).pipe(Effect.provide(LayerNode.compile(CrossSpawnSpawner.node))),
+)
+
+environmentConformance(
+  "GNU exec environment",
+  () =>
+    Effect.gen(function* () {
+      const spawner = yield* ChildProcessSpawner.ChildProcessSpawner
+      const tmp = yield* Effect.promise(() => tmpdir("opencode-environment-"))
+      return {
+        files: execDefaults(spawner),
+        root: tmp.path,
+        symlink: (target: string, link: string) =>
+          Effect.tryPromise({
+            try: () => fs.symlink(target, link),
+            catch: (cause) => new Failed({ path: link, cause }),
+          }),
+        dispose: Effect.promise(() => tmp[Symbol.asyncDispose]()),
+      }
+    }).pipe(Effect.provide(LayerNode.compile(CrossSpawnSpawner.node))),
+  process.platform !== "linux",
+)

packages/core/test/file-mutation.test.ts

@@ -5,7 +5,7 @@ import { Deferred, Effect, Fiber, Layer } from "effect"
 import { AppNodeBuilder } from "@opencode-ai/core/effect/app-node-builder"
 import { LayerNode } from "@opencode-ai/util/effect/layer-node"
 import { FileMutation } from "@opencode-ai/core/file-mutation"
-import { FSUtil } from "@opencode-ai/util/fs-util"
+import { Environment } from "@opencode-ai/core/environment"
 import { Location } from "@opencode-ai/core/location"
 import { LocationMutation } from "@opencode-ai/core/location-mutation"
 import { AbsolutePath } from "@opencode-ai/core/schema"
@@ -13,7 +13,7 @@ import { location } from "./fixture/location"
 import { tmpdir } from "./fixture/tmpdir"
 import { it } from "./lib/effect"
 
-function provide(directory: string, filesystemLayer = LayerNode.compile(FSUtil.node)) {
+function provide(directory: string, environmentLayer = LayerNode.compile(Environment.node)) {
   const activeLocation = Layer.succeed(
     Location.Service,
     Location.Service.of(location({ directory: AbsolutePath.make(directory) })),
@@ -21,7 +21,7 @@ function provide(directory: string, filesystemLayer = LayerNode.compile(FSUtil.n
   return Effect.provide(
     AppNodeBuilder.build(LayerNode.group([LocationMutation.node, FileMutation.node]), [
       [Location.node, activeLocation],
-      [FSUtil.node, filesystemLayer],
+      [Environment.node, environmentLayer],
     ]),
   )
 }
@@ -152,6 +152,57 @@ describe("FileMutation", () => {
     ),
   )
 
+  it.live("shares transaction locks across Location service instances", () =>
+    withTmp((directory) =>
+      Effect.gen(function* () {
+        const firstStarted = yield* Deferred.make<void>()
+        const releaseFirst = yield* Deferred.make<void>()
+        const secondStarted = yield* Deferred.make<void>()
+        const target = path.join(directory, "shared.txt")
+        const first = yield* Effect.gen(function* () {
+          const files = yield* FileMutation.Service
+          yield* files.withLock([target])(
+            Deferred.succeed(firstStarted, undefined).pipe(Effect.andThen(Deferred.await(releaseFirst))),
+          )
+        }).pipe(provide(directory), Effect.forkChild)
+        yield* Deferred.await(firstStarted)
+        const second = yield* Effect.gen(function* () {
+          const files = yield* FileMutation.Service
+          yield* files.withLock([target])(Deferred.succeed(secondStarted, undefined))
+        }).pipe(provide(directory), Effect.forkChild)
+        yield* Effect.yieldNow
+        expect(yield* Deferred.isDone(secondStarted)).toBe(false)
+
+        yield* Deferred.succeed(releaseFirst, undefined)
+        yield* Deferred.await(secondStarted)
+        yield* Fiber.join(first)
+        yield* Fiber.join(second)
+      }),
+    ),
+  )
+
+  it.live("allows transaction locks for distinct resolved paths to proceed independently", () =>
+    withTmp((directory) =>
+      Effect.gen(function* () {
+        const firstStarted = yield* Deferred.make<void>()
+        const releaseFirst = yield* Deferred.make<void>()
+        const secondFinished = yield* Deferred.make<void>()
+        const files = yield* FileMutation.Service
+        const first = yield* files
+          .withLock([path.join(directory, "first.txt")])(
+            Deferred.succeed(firstStarted, undefined).pipe(Effect.andThen(Deferred.await(releaseFirst))),
+          )
+          .pipe(Effect.forkChild)
+        yield* Deferred.await(firstStarted)
+        yield* files.withLock([path.join(directory, "second.txt")])(Deferred.succeed(secondFinished, undefined))
+        expect(yield* Deferred.isDone(secondFinished)).toBe(true)
+
+        yield* Deferred.succeed(releaseFirst, undefined)
+        yield* Fiber.join(first)
+      }).pipe(provide(directory)),
+    ),
+  )
+
   it.live("allows distinct absolute targets to proceed independently", () =>
     withTmp((directory) =>
       Effect.gen(function* () {
@@ -191,16 +242,16 @@ describe("FileMutation", () => {
 
 function instrumentWrites(run: <E>(write: Effect.Effect<void, E>, target: string) => Effect.Effect<void, E>) {
   return Layer.effect(
-    FSUtil.Service,
+    Environment.Service,
     Effect.gen(function* () {
-      const filesystem = yield* FSUtil.Service
-      return FSUtil.Service.of({
-        ...filesystem,
-        writeWithDirs: (target, content, mode) => run(filesystem.writeWithDirs(target, content, mode), target),
-        writeFile: (target, content, options) => run(filesystem.writeFile(target, content, options), target),
-        writeFileString: (target, content, options) =>
-          run(filesystem.writeFileString(target, content, options), target),
+      const environment = yield* Environment.Service
+      return Environment.Service.of({
+        ...environment,
+        files: {
+          ...environment.files,
+          write: (target, content) => run(environment.files.write(target, content), target),
+        },
       })
     }),
-  ).pipe(Layer.provide(LayerNode.compile(FSUtil.node)))
+  ).pipe(Layer.provide(LayerNode.compile(Environment.node)))
 }

packages/core/test/filesystem/watcher.test.ts

@@ -17,9 +17,8 @@ import { location } from "../fixture/location"
 import { tmpdir } from "../fixture/tmpdir"
 import { testEffect } from "../lib/effect"
 
-const describeWatcher = Watcher.hasNativeBinding() && !process.env.CI ? describe : describe.skip
-
 type WatcherEvent = { file: string; event: "add" | "change" | "unlink" }
+const describeNative = process.env.CI ? describe.skip : describe
 
 const it = testEffect(AppNodeBuilder.build(LayerNode.group([FSUtil.node, Bus.node])))
 
@@ -75,10 +74,9 @@ describe("Watcher lifecycle", () => {
       const interrupted = yield* Deferred.make<void>()
       yield* Effect.gen(function* () {
         const watcher = yield* Watcher.Service
-        const consumer = yield* watcher.subscribe({ path: "/pending", type: "directory" }).pipe(
-          Effect.flatMap(Stream.runDrain),
-          Effect.forkScoped({ startImmediately: true }),
-        )
+        const consumer = yield* watcher
+          .subscribe({ path: "/pending", type: "directory" })
+          .pipe(Effect.flatMap(Stream.runDrain), Effect.forkScoped({ startImmediately: true }))
         yield* Deferred.await(started)
         yield* Fiber.interrupt(consumer)
         expect(yield* Deferred.isDone(interrupted)).toBe(true)
@@ -99,10 +97,9 @@ describe("Watcher lifecycle", () => {
     return Effect.gen(function* () {
       const watcher = yield* Watcher.Service
       const consume = () =>
-        watcher.subscribe({ path: "/shared", type: "directory" }).pipe(
-          Effect.flatMap(Stream.runDrain),
-          Effect.forkScoped({ startImmediately: true }),
-        )
+        watcher
+          .subscribe({ path: "/shared", type: "directory" })
+          .pipe(Effect.flatMap(Stream.runDrain), Effect.forkScoped({ startImmediately: true }))
       const first = yield* consume()
       const second = yield* consume()
       yield* Effect.yieldNow
@@ -138,22 +135,26 @@ describe("Watcher lifecycle", () => {
   })
 })
 
-function provide(directory: string, vcs?: Location.Interface["vcs"]) {
+function provide(directory: string, vcs?: Location.Interface["vcs"], watcher?: Layer.Layer<Watcher.Service>) {
   const locationLayer = Layer.succeed(
     Location.Service,
     Location.Service.of(location({ directory: AbsolutePath.make(directory) }, { vcs })),
   )
-  return Effect.provide(
-    AppNodeBuilder.build(LocationWatcher.node, [
-      [Config.node, configLayer],
-      [Location.node, locationLayer],
-    ]),
-  )
+  const built = AppNodeBuilder.build(LocationWatcher.node, [
+    [Config.node, configLayer],
+    [Location.node, locationLayer],
+    ...(watcher ? ([[Watcher.node, watcher]] as const) : []),
+  ])
+  return Effect.provide(built)
 }
 
 function withTmp<A, E, R>(
   f: (directory: string, vcs?: Location.Interface["vcs"]) => Effect.Effect<A, E, R>,
-  options?: { vcs?: "git" | "hg"; init?: (directory: string) => Promise<void> },
+  options?: {
+    vcs?: "git" | "hg"
+    init?: (directory: string) => Promise<void>
+    watcher?: Layer.Layer<Watcher.Service>
+  },
 ) {
   return Effect.acquireRelease(
     Effect.promise(async () => {
@@ -173,9 +174,57 @@ function withTmp<A, E, R>(
       return { tmp, vcs: { type: "git" as const, store: AbsolutePath.make(path.join(tmp.path, ".git")) } }
     }),
     ({ tmp }) => Effect.promise(() => tmp[Symbol.asyncDispose]()),
-  ).pipe(Effect.flatMap(({ tmp, vcs }) => f(tmp.path, vcs).pipe(provide(tmp.path, vcs))))
+  ).pipe(Effect.flatMap(({ tmp, vcs }) => f(tmp.path, vcs).pipe(provide(tmp.path, vcs, options?.watcher))))
 }
 
+describe("LocationWatcher subscriptions", () => {
+  it.live("watches only exact Git branch metadata", () => {
+    const subscriptions: Watcher.WatchInput[] = []
+    const watcher = Layer.succeed(
+      Watcher.Service,
+      Watcher.Service.of({
+        subscribe: (input) => Effect.sync(() => subscriptions.push(input)).pipe(Effect.as(Stream.empty)),
+      }),
+    )
+    return withTmp(
+      (directory) =>
+        Effect.gen(function* () {
+          yield* LocationWatcher.Service
+          yield* Effect.sync(() => subscriptions.length).pipe(
+            Effect.filterOrFail((count) => count > 0),
+            Effect.retry(Schedule.spaced("10 millis")),
+          )
+          yield* Effect.sleep("10 millis")
+          expect(subscriptions).toEqual([{ path: path.join(directory, ".git", "HEAD"), type: "file" }])
+        }),
+      { vcs: "git", watcher },
+    )
+  })
+
+  it.live("watches only exact Hg branch metadata", () => {
+    const subscriptions: Watcher.WatchInput[] = []
+    const watcher = Layer.succeed(
+      Watcher.Service,
+      Watcher.Service.of({
+        subscribe: (input) => Effect.sync(() => subscriptions.push(input)).pipe(Effect.as(Stream.empty)),
+      }),
+    )
+    return withTmp(
+      (directory) =>
+        Effect.gen(function* () {
+          yield* LocationWatcher.Service
+          yield* Effect.sync(() => subscriptions.length).pipe(
+            Effect.filterOrFail((count) => count > 0),
+            Effect.retry(Schedule.spaced("10 millis")),
+          )
+          yield* Effect.sleep("10 millis")
+          expect(subscriptions).toEqual([{ path: path.join(directory, ".hg", "branch"), type: "file" }])
+        }),
+      { vcs: "hg", watcher },
+    )
+  })
+})
+
 function wait(check: (event: WatcherEvent) => boolean) {
   return Effect.gen(function* () {
     const bus = yield* Bus.Service
@@ -226,31 +275,18 @@ function eventuallyUpdate<E>(check: (event: WatcherEvent) => boolean, trigger: (
   )
 }
 
-function noUpdate<E>(check: (event: WatcherEvent) => boolean, trigger: Effect.Effect<void, E>, timeout = 500) {
-  return Effect.acquireUseRelease(
-    wait(check),
-    ({ deferred }) =>
-      trigger.pipe(
-        Effect.andThen(Deferred.await(deferred)),
-        Effect.timeoutOption(`${timeout} millis`),
-        Effect.tap((result) => Effect.sync(() => expect(result).toEqual(Option.none()))),
-      ),
-    ({ fiber }) => Fiber.interrupt(fiber),
-  )
-}
-
-function ready(directory: string) {
-  const file = path.join(directory, `.watcher-${Math.random().toString(36).slice(2)}`)
+function ready(file: string, eventFile = file) {
   return Effect.gen(function* () {
     const fs = yield* FSUtil.Service
+    const content = (yield* fs.readFileStringSafe(file)) ?? `ready-${Math.random()}`
     yield* eventuallyUpdate(
-      (event) => event.file === file,
-      () => fs.writeFileString(file, `ready-${Math.random()}`),
-    ).pipe(Effect.ensuring(fs.remove(file, { force: true }).pipe(Effect.ignore)), Effect.asVoid)
+      (event) => event.file === eventFile,
+      () => fs.writeFileString(file, content),
+    ).pipe(Effect.asVoid)
   })
 }
 
-describeWatcher("LocationWatcher", () => {
+describeNative("LocationWatcher", () => {
   it.live("limits file watches to the exact target", () =>
     withTmp((directory) =>
       Effect.gen(function* () {
@@ -276,94 +312,25 @@ describeWatcher("LocationWatcher", () => {
     ),
   )
 
-  it.live("publishes root create, update, and delete events", () =>
-    withTmp(
-      (directory) =>
-        Effect.gen(function* () {
-          const fs = yield* FSUtil.Service
-          const file = path.join(directory, "watch.txt")
-          yield* ready(directory)
-          for (const item of [
-            { event: "add" as const, trigger: fs.writeFileString(file, "a") },
-            { event: "change" as const, trigger: fs.writeFileString(file, "b") },
-            { event: "unlink" as const, trigger: fs.remove(file) },
-          ]) {
-            expect(
-              yield* nextUpdate((event) => event.file === file && event.event === item.event, item.trigger),
-            ).toEqual({
-              file,
-              event: item.event,
-            })
-          }
-        }),
-      { vcs: "git" },
-    ),
-  )
-
-  it.live("skips non-git roots", () =>
+  it.live("detects creation of a missing directory target", () =>
     withTmp((directory) =>
       Effect.gen(function* () {
         const fs = yield* FSUtil.Service
-        const file = path.join(directory, "plain.txt")
-        yield* noUpdate((event) => event.file === file, fs.writeFileString(file, "plain"))
-      }),
-    ),
-  )
+        const watcher = yield* Watcher.Service
+        const target = path.join(directory, "generated")
+        const updates = yield* watcher.subscribe({ path: target, type: "file" })
+        const update = yield* updates.pipe(
+          Stream.take(1),
+          Stream.runHead,
+          Effect.forkScoped({ startImmediately: true }),
+        )
+        const creates = yield* Effect.suspend(() =>
+          fs.remove(target, { recursive: true, force: true }).pipe(Effect.andThen(fs.ensureDir(target))),
+        ).pipe(Effect.repeat(Schedule.spaced("10 millis")), Effect.forkScoped)
+        const event = yield* Fiber.join(update).pipe(Effect.ensuring(Fiber.interrupt(creates)))
 
-  it.live("ignores dependency, VCS, and build directories at any depth", () =>
-    withTmp(
-      (directory) =>
-        Effect.gen(function* () {
-          const afs = yield* FSUtil.Service
-          yield* ready(directory)
-          const roots = ["node_modules", ".git", "dist"].map((name) => path.join(directory, "nested", name))
-          const files = roots.map((root) => path.join(root, "package", "index.js"))
-          yield* noUpdate(
-            (event) => roots.some((root) => event.file === root || event.file.startsWith(`${root}${path.sep}`)),
-            Effect.forEach(files, (file) => afs.writeWithDirs(file, "ignored"), {
-              concurrency: "unbounded",
-              discard: true,
-            }),
-          )
-        }),
-      { vcs: "git" },
-    ),
-  )
-
-  it.live("cleanup stops publishing events", () =>
-    Effect.gen(function* () {
-      const bus = yield* Bus.Service
-      const fs = yield* FSUtil.Service
-      const tmp = yield* Effect.acquireRelease(
-        Effect.promise(() => tmpdir()),
-        (tmp) => Effect.promise(() => tmp[Symbol.asyncDispose]()),
-      )
-      yield* ready(tmp.path).pipe(
-        provide(tmp.path, { type: "git", store: AbsolutePath.make(path.join(tmp.path, ".git")) }),
-        Effect.scoped,
-      )
-      const file = path.join(tmp.path, "after-dispose.txt")
-      yield* noUpdate((event) => event.file === file, fs.writeFileString(file, "gone")).pipe(
-        Effect.provideService(Bus.Service, bus),
-      )
-    }).pipe(Effect.provide(AppNodeBuilder.build(LayerNode.group([FSUtil.node, Bus.node])))),
-  )
-
-  it.live("ignores .git/index changes", () =>
-    withTmp(
-      (directory) =>
-        Effect.gen(function* () {
-          const fs = yield* FSUtil.Service
-          const index = path.join(directory, ".git", "index")
-          yield* ready(directory)
-          yield* noUpdate(
-            (event) => event.file === index,
-            fs
-              .writeFileString(path.join(directory, "tracked.txt"), "a")
-              .pipe(Effect.andThen(Effect.promise(() => $`git add .`.cwd(directory).quiet())), Effect.asVoid),
-          )
-        }),
-      { vcs: "git" },
+        expect(event.valueOrUndefined?.path).toBe(target)
+      }).pipe(Effect.provide(AppNodeBuilder.build(Watcher.node))),
     ),
   )
 
@@ -374,11 +341,11 @@ describeWatcher("LocationWatcher", () => {
           const fs = yield* FSUtil.Service
           const head = path.join(directory, ".git", "HEAD")
           const branch = `watch-${Math.random().toString(36).slice(2)}`
-          yield* ready(directory)
+          yield* ready(head)
           yield* Effect.promise(() => $`git branch ${branch}`.cwd(directory).quiet())
           expect(
             yield* nextUpdate((event) => event.file === head, fs.writeFileString(head, `ref: refs/heads/${branch}\n`)),
-          ).toMatchObject({ file: head })
+          ).toEqual({ file: head, event: "change" })
         }),
       { vcs: "git" },
     ),
@@ -393,8 +360,8 @@ describeWatcher("LocationWatcher", () => {
             const afs = yield* FSUtil.Service
             const actual = path.join(directory, "..", `actual_${path.basename(directory)}`)
             yield* Effect.addFinalizer(() => Effect.promise(() => fs.rm(actual, { recursive: true, force: true })))
-            yield* ready(directory)
             const head = path.join(directory, ".git", "HEAD")
+            yield* ready(head, path.join(actual, "HEAD"))
             const branch = `watch-${Math.random().toString(36).slice(2)}`
             yield* Effect.promise(() => $`git branch ${branch}`.cwd(directory).quiet())
             expect(
@@ -422,7 +389,7 @@ describeWatcher("LocationWatcher", () => {
         Effect.gen(function* () {
           const fs = yield* FSUtil.Service
           const branch = path.join(directory, ".hg", "branch")
-          yield* ready(directory)
+          yield* ready(branch)
           expect(
             yield* nextUpdate((event) => event.file === branch, fs.writeFileString(branch, "feature\n")),
           ).toMatchObject({ file: branch })

packages/core/test/lib/environment-conformance.ts

@@ -0,0 +1,169 @@
+import { describe, expect } from "bun:test"
+import { Effect } from "effect"
+import { Failed, NotFound, WrongKind, type Files } from "../../src/environment/index"
+import { it } from "./effect"
+
+export interface EnvironmentHarness {
+  readonly files: Files
+  readonly root: string
+  readonly symlink?: (target: string, path: string) => Effect.Effect<void, Failed>
+  readonly dispose?: Effect.Effect<void>
+}
+
+export const environmentConformance = <E>(
+  name: string,
+  makeHarness: () => Effect.Effect<EnvironmentHarness, E>,
+  skip = false,
+) => {
+  const check = <A, E2>(title: string, body: (harness: EnvironmentHarness) => Effect.Effect<A, E2>) =>
+    it.live(title, () =>
+      Effect.gen(function* () {
+        const harness = yield* Effect.acquireRelease(makeHarness(), (harness) =>
+          Effect.gen(function* () {
+            yield* Effect.ignore(harness.files.remove(harness.root))
+            if (harness.dispose) yield* harness.dispose
+          }),
+        )
+        yield* harness.files.mkdir(harness.root)
+        return yield* body(harness)
+      }),
+    )
+
+  const bytes = (value: string) => new TextEncoder().encode(value)
+  const text = (value: Uint8Array) => new TextDecoder().decode(value)
+  const suite = skip ? describe.skip : describe
+
+  suite(name, () => {
+    check("writes, stats, and reads a file with its info", (harness) =>
+      Effect.gen(function* () {
+        const target = `${harness.root}/hello.txt`
+        yield* harness.files.write(target, bytes("hello"))
+        const result = yield* harness.files.read(target)
+        expect(text(result.bytes)).toBe("hello")
+        expect(result.info.type).toBe("file")
+        expect(result.info.size).toBe(5)
+        expect(yield* harness.files.stat(target)).toEqual(result.info)
+      }),
+    )
+
+    check("reports missing paths", (harness) =>
+      Effect.gen(function* () {
+        const target = `${harness.root}/missing`
+        expect(yield* Effect.flip(harness.files.read(target))).toBeInstanceOf(NotFound)
+        expect(yield* Effect.flip(harness.files.stat(target))).toBeInstanceOf(NotFound)
+        expect(yield* Effect.flip(harness.files.list(target))).toBeInstanceOf(NotFound)
+        expect(yield* Effect.flip(harness.files.move(target, `${harness.root}/other`))).toBeInstanceOf(NotFound)
+      }),
+    )
+
+    check("reports the actual kind", (harness) =>
+      Effect.gen(function* () {
+        const directory = `${harness.root}/directory`
+        const file = `${harness.root}/file`
+        yield* harness.files.mkdir(directory)
+        yield* harness.files.write(file, bytes("data"))
+        const readError = yield* Effect.flip(harness.files.read(directory))
+        const listError = yield* Effect.flip(harness.files.list(file))
+        expect(readError).toBeInstanceOf(WrongKind)
+        expect((readError as WrongKind).actual).toBe("directory")
+        expect(listError).toBeInstanceOf(WrongKind)
+        expect((listError as WrongKind).actual).toBe("file")
+      }),
+    )
+
+    check("write creates parent directories", (harness) =>
+      Effect.gen(function* () {
+        const target = `${harness.root}/one/two/file`
+        yield* harness.files.write(target, bytes("nested"))
+        yield* harness.files.write(`${harness.root}/empty`, new Uint8Array())
+        expect((yield* harness.files.stat(`${harness.root}/one/two`)).type).toBe("directory")
+        expect(yield* harness.files.stat(`${harness.root}/empty`)).toMatchObject({ type: "file", size: 0 })
+        expect(text((yield* harness.files.read(target)).bytes)).toBe("nested")
+      }),
+    )
+
+    check("reads byte ranges", (harness) =>
+      Effect.gen(function* () {
+        const target = `${harness.root}/range`
+        yield* harness.files.write(target, bytes("0123456789"))
+        expect(text((yield* harness.files.read(target, { offset: 2, length: 4 })).bytes)).toBe("2345")
+        expect(text((yield* harness.files.read(target, { offset: 8, length: 8 })).bytes)).toBe("89")
+        expect(text((yield* harness.files.read(target, { offset: 20, length: 4 })).bytes)).toBe("")
+      }),
+    )
+
+    check("lists immediate entries with their kinds", (harness) =>
+      Effect.gen(function* () {
+        yield* harness.files.write(`${harness.root}/file name`, bytes("data"))
+        yield* harness.files.mkdir(`${harness.root}/directory`)
+        yield* harness.files.write(`${harness.root}/directory/nested`, bytes("nested"))
+        const entries = yield* harness.files.list(harness.root)
+        expect(entries.toSorted((a, b) => a.name.localeCompare(b.name))).toEqual([
+          { name: "directory", type: "directory" },
+          { name: "file name", type: "file" },
+        ])
+      }),
+    )
+
+    check("preserves symlink metadata while following symlinks for content", (harness) =>
+      Effect.gen(function* () {
+        if (!harness.symlink) return
+        yield* harness.files.write(`${harness.root}/target`, bytes("target"))
+        yield* harness.files.write(`${harness.root}/target-dir/file`, bytes("through link"))
+        yield* harness.symlink("../target", `${harness.root}/target-dir/entry-link`)
+        yield* harness.symlink("target", `${harness.root}/link`)
+        yield* harness.symlink("target-dir", `${harness.root}/link-dir`)
+        yield* harness.symlink("missing", `${harness.root}/dangling-link`)
+        expect((yield* harness.files.stat(`${harness.root}/link`)).type).toBe("symlink")
+        expect(yield* harness.files.list(harness.root)).toContainEqual({ name: "link", type: "symlink" })
+        expect(text((yield* harness.files.read(`${harness.root}/link-dir/file`)).bytes)).toBe("through link")
+        expect(
+          (yield* harness.files.list(`${harness.root}/link-dir`)).toSorted((a, b) => a.name.localeCompare(b.name)),
+        ).toEqual([
+          { name: "entry-link", type: "symlink" },
+          { name: "file", type: "file" },
+        ])
+
+        const fileError = yield* Effect.flip(harness.files.list(`${harness.root}/link`))
+        expect(fileError).toBeInstanceOf(WrongKind)
+        expect((fileError as WrongKind).actual).toBe("file")
+        expect(yield* Effect.flip(harness.files.list(`${harness.root}/dangling-link`))).toBeInstanceOf(NotFound)
+      }),
+    )
+
+    check("follows symlinks when reading", (harness) =>
+      Effect.gen(function* () {
+        if (!harness.symlink) return
+        yield* harness.files.write(`${harness.root}/target`, bytes("target content"))
+        yield* harness.files.mkdir(`${harness.root}/directory`)
+        yield* harness.symlink("target", `${harness.root}/file-link`)
+        yield* harness.symlink("directory", `${harness.root}/directory-link`)
+        yield* harness.symlink("missing", `${harness.root}/dangling-link`)
+
+        const result = yield* harness.files.read(`${harness.root}/file-link`)
+        expect(text(result.bytes)).toBe("target content")
+        expect(result.info.type).toBe("file")
+        expect(result.info.size).toBe(bytes("target content").length)
+
+        const directoryError = yield* Effect.flip(harness.files.read(`${harness.root}/directory-link`))
+        expect(directoryError).toBeInstanceOf(WrongKind)
+        expect((directoryError as WrongKind).actual).toBe("directory")
+        expect(yield* Effect.flip(harness.files.read(`${harness.root}/dangling-link`))).toBeInstanceOf(NotFound)
+      }),
+    )
+
+    check("moves files and removes trees idempotently", (harness) =>
+      Effect.gen(function* () {
+        const source = `${harness.root}/source/file`
+        const destination = `${harness.root}/destination`
+        yield* harness.files.write(source, bytes("moved"))
+        yield* harness.files.move(source, destination)
+        expect(text((yield* harness.files.read(destination)).bytes)).toBe("moved")
+        expect(yield* Effect.flip(harness.files.stat(source))).toBeInstanceOf(NotFound)
+        yield* harness.files.remove(`${harness.root}/source`)
+        yield* harness.files.remove(`${harness.root}/source`)
+        expect(yield* Effect.flip(harness.files.stat(`${harness.root}/source`))).toBeInstanceOf(NotFound)
+      }),
+    )
+  })
+}

packages/core/test/session-execution.test.ts

@@ -13,6 +13,7 @@ import { Session } from "@opencode-ai/core/session"
 import { SessionExecution } from "@opencode-ai/core/session/execution"
 import { SessionRestart } from "@opencode-ai/core/session/execution/restart"
 import { UserInterruptedError } from "@opencode-ai/core/session/error"
+import { SessionEvent } from "@opencode-ai/core/session/event"
 import { SessionRunner } from "@opencode-ai/core/session/runner"
 import { SessionTable } from "@opencode-ai/core/session/sql"
 import { SessionStore } from "@opencode-ai/core/session/store"
@@ -127,23 +128,34 @@ describe("SessionExecution lifecycle", () => {
   it.effect("resumes each suspended Session at most once", () =>
     Effect.gen(function* () {
       const database = yield* Database.Service
+      const bus = yield* Bus.Service
       const first = Session.ID.make("ses_resume_first")
       const second = Session.ID.make("ses_resume_second")
       yield* seedSessions(database, [first, second], { time_suspended: Date.now() })
 
       const drained: string[] = []
+      const continued: SessionEvent.Synthetic[] = []
       const scope = yield* Scope.make()
       const context = yield* buildExecution(scope, ({ sessionID }) => Effect.sync(() => void drained.push(sessionID)))
       const execution = Context.get(context, SessionExecution.Service)
       const restart = Context.get(context, SessionRestart.Service)
+      yield* bus.project(SessionEvent.Synthetic, (event) => Effect.sync(() => void continued.push(event)))
 
       yield* restart.resumeSuspendedSessions
       yield* Effect.forEach([first, second], execution.awaitIdle, { discard: true })
       expect(drained.toSorted()).toEqual([first, second])
+      expect(continued.map((event) => event.data).toSorted((a, b) => a.sessionID.localeCompare(b.sessionID))).toEqual(
+        [first, second].map((sessionID) => ({
+          sessionID,
+          text: "The server restarted while you were working. Continue from where you left off without repeating completed work.",
+          description: "Continuing after restart",
+        })),
+      )
       expect(yield* suspensions(database)).toEqual({ [first]: false, [second]: false })
 
       yield* restart.resumeSuspendedSessions
       expect(drained.length).toBe(2)
+      expect(continued.length).toBe(2)
       yield* Scope.close(scope, Exit.void)
     }),
   )

packages/core/test/session-prompt.test.ts

@@ -1086,4 +1086,78 @@ describe("Session.pending", () => {
       expect(yield* session.pending(sessionID)).toEqual([])
     }),
   )
+
+  it.effect("cancels pending input and allows its ID to be admitted again", () =>
+    Effect.gen(function* () {
+      yield* setup
+      const session = yield* Session.Service
+      const inputID = SessionMessage.ID.make("msg_cancelled_queue")
+      yield* session.prompt({
+        id: inputID,
+        sessionID,
+        text: "Queue this",
+        delivery: "queue",
+        resume: false,
+      })
+
+      yield* session.cancelPending({ sessionID, inputID })
+
+      expect(yield* session.pending(sessionID)).toEqual([])
+      expect(yield* eventCount(Bus.versionedType(SessionEvent.InputCancelled.type, 1))).toBe(1)
+      expect(
+        yield* session.cancelPending({ sessionID, inputID }).pipe(Effect.flip),
+      ).toMatchObject({ _tag: "Session.PendingInputConflictError", sessionID, inputID })
+      expect(yield* eventCount(Bus.versionedType(SessionEvent.InputCancelled.type, 1))).toBe(1)
+
+      const retried = yield* session.prompt({
+        id: inputID,
+        sessionID,
+        text: "Queue this",
+        delivery: "queue",
+        resume: false,
+      })
+      expect(retried).toMatchObject({ id: inputID, delivery: "queue" })
+    }),
+  )
+
+  it.effect("moves pending input between steer and queue delivery", () =>
+    Effect.gen(function* () {
+      yield* setup
+      const session = yield* Session.Service
+      const queued = yield* session.synthetic({
+        sessionID,
+        text: "Steer this",
+        delivery: "queue",
+        resume: false,
+      })
+      const alreadySteered = yield* session.prompt({ sessionID, text: "Already steer", resume: false })
+      wakeCalls.length = 0
+
+      yield* session.steerPending({ sessionID, inputID: queued.id })
+
+      expect(yield* session.pending(sessionID)).toMatchObject([
+        { id: queued.id, delivery: "steer" },
+        { id: alreadySteered.id, delivery: "steer" },
+      ])
+      expect(wakeCalls).toEqual([sessionID])
+      expect(yield* eventCount(Bus.versionedType(SessionEvent.InputSteered.type, 1))).toBe(1)
+
+      wakeCalls.length = 0
+      yield* session.queuePending({ sessionID, inputID: queued.id })
+      expect(yield* session.pending(sessionID)).toMatchObject([
+        { id: queued.id, delivery: "queue" },
+        { id: alreadySteered.id, delivery: "steer" },
+      ])
+      expect(wakeCalls).toEqual([])
+      expect(yield* eventCount(Bus.versionedType(SessionEvent.InputQueued.type, 1))).toBe(1)
+
+      expect(
+        yield* session.steerPending({ sessionID, inputID: alreadySteered.id }).pipe(Effect.flip),
+      ).toMatchObject({ _tag: "Session.PendingInputConflictError", sessionID, inputID: alreadySteered.id })
+      yield* session.cancelPending({ sessionID, inputID: alreadySteered.id })
+      expect(wakeCalls).toEqual([])
+      expect(yield* eventCount(Bus.versionedType(SessionEvent.InputSteered.type, 1))).toBe(1)
+      expect(yield* eventCount(Bus.versionedType(SessionEvent.InputCancelled.type, 1))).toBe(1)
+    }),
+  )
 })

packages/core/test/skill.test.ts

@@ -6,11 +6,10 @@ import { Agent } from "@opencode-ai/core/agent"
 import { AppNodeBuilder } from "@opencode-ai/core/effect/app-node-builder"
 import { LayerNode } from "@opencode-ai/util/effect/layer-node"
 import { Bus } from "@opencode-ai/core/bus"
-import { FSUtil } from "@opencode-ai/util/fs-util"
 import { AbsolutePath } from "@opencode-ai/core/schema"
 import { Skill } from "@opencode-ai/core/skill"
 import { SkillDiscovery } from "@opencode-ai/core/skill/discovery"
-import { FileSystem } from "@opencode-ai/schema/filesystem"
+import { Watcher } from "@opencode-ai/core/filesystem/watcher"
 import { tmpdir } from "./fixture/tmpdir"
 import { testEffect } from "./lib/effect"
 
@@ -25,8 +24,15 @@ const discovery = Layer.succeed(
     },
   }),
 )
+const watcherLayer = Watcher.testLayer
 const it = testEffect(
-  AppNodeBuilder.build(LayerNode.group([Skill.node, Agent.node, Bus.node]), [[SkillDiscovery.node, discovery]]),
+  Layer.mergeAll(
+    AppNodeBuilder.build(LayerNode.group([Skill.node, Agent.node, Bus.node]), [
+      [SkillDiscovery.node, discovery],
+      [Watcher.node, watcherLayer],
+    ]),
+    watcherLayer,
+  ),
 )
 
 function write(directory: string, name: string, description: string) {
@@ -53,6 +59,24 @@ function waitForSkillUpdate() {
   })
 }
 
+function expectSubscription(check: (input: Watcher.WatchInput) => boolean) {
+  return Effect.gen(function* () {
+    const watcher = yield* Watcher.Test
+    expect((yield* watcher.subscriptions()).some(check)).toBe(true)
+  })
+}
+
+function emitAndWait(update: Watcher.Update) {
+  return Effect.gen(function* () {
+    const watcher = yield* Watcher.Test
+    yield* Effect.acquireUseRelease(
+      waitForSkillUpdate(),
+      ({ deferred }) => watcher.emit(update).pipe(Effect.andThen(Deferred.await(deferred)), Effect.timeout("1 second")),
+      ({ fiber }) => Fiber.interrupt(fiber),
+    )
+  })
+}
+
 describe("Skill", () => {
   it.live("publishes updates when skill sources change", () =>
     Effect.gen(function* () {
@@ -89,6 +113,7 @@ describe("Skill", () => {
           })
 
           const skill = yield* Skill.Service
+          const watcher = yield* Watcher.Test
           yield* skill.transform((editor) => {
             editor.source({ type: "directory", path: AbsolutePath.make(first) })
             editor.source({ type: "directory", path: AbsolutePath.make(first) })
@@ -119,6 +144,21 @@ describe("Skill", () => {
               content: "# review",
             },
           ])
+          expect(yield* watcher.subscriptions()).toEqual([
+            { path: first, type: "directory" },
+            { path: second, type: "directory" },
+          ])
+
+          yield* Effect.promise(() => write(second, "review", "Updated Second"))
+          yield* emitAndWait({ type: "update", path: path.join(second, "review", "SKILL.md") })
+
+          expect((yield* skill.list()).find((item) => item.id === "review")?.description).toBe("Updated Second")
+          expect(yield* watcher.subscriptions()).toEqual([
+            { path: first, type: "directory" },
+            { path: second, type: "directory" },
+            { path: first, type: "directory" },
+            { path: second, type: "directory" },
+          ])
         }),
       ),
     ),
@@ -198,7 +238,7 @@ metadata:
     ),
   )
 
-  it.live("invalidates cached skills and publishes updates for watcher changes", () =>
+  it.live("clears cached skills when sources reload", () =>
     Effect.acquireRelease(
       Effect.promise(() => tmpdir()),
       (tmp) => Effect.promise(() => tmp[Symbol.asyncDispose]()),
@@ -210,26 +250,187 @@ metadata:
             await write(tmp.path, "deploy", "Initial deploy")
           })
 
+          const skill = yield* Skill.Service
+          const watcher = yield* Watcher.Test
           const bus = yield* Bus.Service
+          yield* skill.transform((editor) => editor.source({ type: "directory", path: AbsolutePath.make(tmp.path) }))
+          expect((yield* skill.list()).find((item) => item.id === "deploy")?.description).toBe("Initial deploy")
+          expect(yield* watcher.subscriptions()).toEqual([{ path: tmp.path, type: "directory" }])
+
+          let refreshed: Skill.Info[] = []
+          const unsubscribe = yield* bus.listen((event) => {
+            if (event.type !== Skill.Event.Updated.type) return Effect.void
+            return skill.list().pipe(
+              Effect.tap((items) => Effect.sync(() => (refreshed = items))),
+              Effect.asVoid,
+            )
+          })
+
+          yield* Effect.promise(() => write(tmp.path, "deploy", "Updated deploy"))
+          yield* skill.reload().pipe(Effect.timeout("1 second"))
+          yield* unsubscribe
+
+          expect(refreshed.find((item) => item.id === "deploy")?.description).toBe("Updated deploy")
+          expect(yield* watcher.subscriptions()).toEqual([
+            { path: tmp.path, type: "directory" },
+            { path: tmp.path, type: "directory" },
+          ])
+        }),
+      ),
+    ),
+  )
+
+  it.live("reloads project sources created after their missing parent", () =>
+    Effect.acquireRelease(
+      Effect.promise(() => tmpdir()),
+      (tmp) => Effect.promise(() => tmp[Symbol.asyncDispose]()),
+    ).pipe(
+      Effect.flatMap((tmp) =>
+        Effect.gen(function* () {
+          const source = path.join(tmp.path, "generated", "skills")
+          const file = path.join(source, "deploy", "SKILL.md")
+          const skill = yield* Skill.Service
+          const watcher = yield* Watcher.Test
+          yield* skill.transform((editor) => editor.source({ type: "directory", path: AbsolutePath.make(source) }))
+          expect(yield* skill.list()).toEqual([])
+          expect(yield* watcher.subscriptions()).toEqual([{ path: path.join(tmp.path, "generated"), type: "file" }])
+
+          yield* Effect.promise(() => fs.mkdir(path.join(tmp.path, "generated")))
+          yield* emitAndWait({ type: "create", path: path.join(tmp.path, "generated") })
+          expect(yield* skill.list()).toEqual([])
+          expect(yield* watcher.subscriptions()).toEqual([
+            { path: path.join(tmp.path, "generated"), type: "file" },
+            { path: source, type: "file" },
+          ])
+
+          yield* Effect.promise(async () => {
+            await fs.mkdir(path.dirname(file), { recursive: true })
+            await write(source, "deploy", "Deploy production")
+          })
+          yield* emitAndWait({ type: "create", path: source })
+
+          expect((yield* skill.list()).map((item) => item.id)).toEqual([Skill.ID.make("deploy")])
+          expect(yield* watcher.subscriptions()).toEqual([
+            { path: path.join(tmp.path, "generated"), type: "file" },
+            { path: source, type: "file" },
+            { path: source, type: "directory" },
+          ])
+        }),
+      ),
+    ),
+  )
+
+  it.live("watches directory sources for added and changed skills", () =>
+    Effect.acquireRelease(
+      Effect.promise(() => tmpdir()),
+      (tmp) => Effect.promise(() => tmp[Symbol.asyncDispose]()),
+    ).pipe(
+      Effect.flatMap((tmp) =>
+        Effect.gen(function* () {
+          yield* Effect.promise(async () => {
+            await fs.mkdir(path.join(tmp.path, "deploy"), { recursive: true })
+            await write(tmp.path, "deploy", "Initial deploy")
+          })
+
           const skill = yield* Skill.Service
           yield* skill.transform((editor) => editor.source({ type: "directory", path: AbsolutePath.make(tmp.path) }))
+          expect((yield* skill.list()).map((item) => item.id)).toEqual([Skill.ID.make("deploy")])
+          yield* expectSubscription((input) => input.type === "directory" && input.path === tmp.path)
 
-          expect((yield* skill.list()).find((item) => item.name === "deploy")?.description).toBe("Initial deploy")
-
-          const file = path.join(tmp.path, "deploy", "SKILL.md")
+          const deploy = path.join(tmp.path, "deploy", "SKILL.md")
           yield* Effect.promise(() => write(tmp.path, "deploy", "Updated deploy"))
-          expect((yield* skill.list()).find((item) => item.name === "deploy")?.description).toBe("Initial deploy")
+          yield* emitAndWait({ type: "update", path: deploy })
+          expect((yield* skill.list()).find((item) => item.id === "deploy")?.description).toBe("Updated deploy")
 
-          yield* Effect.acquireUseRelease(
-            waitForSkillUpdate(),
-            ({ deferred }) =>
-              bus
-                .publish(FileSystem.Event.Changed, { file, event: "change" })
-                .pipe(Effect.andThen(Deferred.await(deferred)), Effect.timeout("1 second")),
-            ({ fiber }) => Fiber.interrupt(fiber),
-          )
+          yield* Effect.promise(async () => {
+            await fs.mkdir(path.join(tmp.path, "review"), { recursive: true })
+            await write(tmp.path, "review", "Review changes")
+          })
+          const review = path.join(tmp.path, "review", "SKILL.md")
+          yield* emitAndWait({ type: "create", path: review })
+          expect((yield* skill.list()).map((item) => item.id)).toEqual([
+            Skill.ID.make("deploy"),
+            Skill.ID.make("review"),
+          ])
 
-          expect((yield* skill.list()).find((item) => item.name === "deploy")?.description).toBe("Updated deploy")
+          yield* Effect.promise(() => fs.rm(path.join(tmp.path, "review"), { recursive: true }))
+          yield* emitAndWait({ type: "delete", path: review })
+          expect((yield* skill.list()).map((item) => item.id)).toEqual([Skill.ID.make("deploy")])
+        }),
+      ),
+    ),
+  )
+
+  it.live("watches canonical directories behind symlinked skills", () =>
+    Effect.acquireRelease(
+      Effect.promise(() => tmpdir()),
+      (tmp) => Effect.promise(() => tmp[Symbol.asyncDispose]()),
+    ).pipe(
+      Effect.flatMap((tmp) =>
+        Effect.gen(function* () {
+          const source = path.join(tmp.path, "source")
+          const target = path.join(tmp.path, "target", "bro")
+          const file = path.join(target, "SKILL.md")
+          yield* Effect.promise(async () => {
+            await fs.mkdir(source, { recursive: true })
+            await fs.mkdir(target, { recursive: true })
+            await fs.writeFile(file, "---\nname: bro\ndescription: Initial\n---\n# bro")
+            await fs.symlink(target, path.join(source, "bro"))
+          })
+
+          const skill = yield* Skill.Service
+          yield* skill.transform((editor) => editor.source({ type: "directory", path: AbsolutePath.make(source) }))
+          expect((yield* skill.list()).find((item) => item.id === "bro")?.description).toBe("Initial")
+          yield* expectSubscription((input) => input.type === "directory" && input.path === target)
+
+          yield* Effect.promise(() => fs.writeFile(file, "---\nname: bro\ndescription: Updated\n---\n# bro"))
+          yield* emitAndWait({ type: "update", path: file })
+          expect((yield* skill.list()).find((item) => item.id === "bro")?.description).toBe("Updated")
+        }),
+      ),
+    ),
+  )
+
+  it.live("invalidates symlinked sources when their target changes", () =>
+    Effect.acquireRelease(
+      Effect.promise(() => tmpdir()),
+      (tmp) => Effect.promise(() => tmp[Symbol.asyncDispose]()),
+    ).pipe(
+      Effect.flatMap((tmp) =>
+        Effect.gen(function* () {
+          const source = path.join(tmp.path, "source")
+          const first = path.join(tmp.path, "first")
+          const second = path.join(tmp.path, "second")
+          yield* Effect.promise(async () => {
+            await fs.mkdir(path.join(first, "bro"), { recursive: true })
+            await fs.mkdir(path.join(second, "bro"), { recursive: true })
+            await write(first, "bro", "First")
+            await write(second, "bro", "Second")
+            await fs.symlink(first, source)
+          })
+
+          const skill = yield* Skill.Service
+          const watcher = yield* Watcher.Test
+          yield* skill.transform((editor) => editor.source({ type: "directory", path: AbsolutePath.make(source) }))
+          expect((yield* skill.list()).find((item) => item.id === "bro")?.description).toBe("First")
+          expect(yield* watcher.subscriptions()).toEqual([
+            { path: first, type: "directory" },
+            { path: source, type: "file" },
+          ])
+
+          yield* Effect.promise(async () => {
+            await fs.unlink(source)
+            await fs.symlink(second, source)
+          })
+          yield* emitAndWait({ type: "update", path: source })
+
+          expect((yield* skill.list()).find((item) => item.id === "bro")?.description).toBe("Second")
+          expect(yield* watcher.subscriptions()).toEqual([
+            { path: first, type: "directory" },
+            { path: source, type: "file" },
+            { path: second, type: "directory" },
+            { path: source, type: "file" },
+          ])
         }),
       ),
     ),

packages/core/test/tool-edit.test.ts

@@ -4,9 +4,9 @@ import { describe, expect } from "bun:test"
 import { Effect, Layer } from "effect"
 import { AppNodeBuilder } from "@opencode-ai/core/effect/app-node-builder"
 import { LayerNode } from "@opencode-ai/util/effect/layer-node"
+import { Environment } from "@opencode-ai/core/environment"
 import { FileMutation } from "@opencode-ai/core/file-mutation"
 import { Formatter } from "@opencode-ai/core/formatter"
-import { FSUtil } from "@opencode-ai/util/fs-util"
 import { Location } from "@opencode-ai/core/location"
 import { LocationMutation } from "@opencode-ai/core/location-mutation"
 import { Permission } from "@opencode-ai/core/permission"
@@ -23,7 +23,15 @@ import { toolIdentity, executeTool, registerToolPlugin, toolDefinitions } from "
 const editToolNode = makeLocationNode({
   name: "test/edit-tool-plugin",
   layer: Layer.effectDiscard(registerToolPlugin(EditTool.Plugin)),
-  deps: [Tool.node, LocationMutation.node, FileMutation.node, Formatter.node, FSUtil.node, Permission.node],
+  deps: [
+    Tool.node,
+    LocationMutation.node,
+    FileMutation.node,
+    Environment.node,
+    Formatter.node,
+    Location.node,
+    Permission.node,
+  ],
 })
 
 const sessionID = Session.ID.make("ses_edit_tool_test")
@@ -72,29 +80,28 @@ const reset = () => {
   formatFile = () => Effect.succeed(false)
 }
 
-const filesystem = Layer.effect(
-  FSUtil.Service,
+const environment = Layer.effect(
+  Environment.Service,
   Effect.gen(function* () {
-    const fs = yield* FSUtil.Service
-    return FSUtil.Service.of({
-      ...fs,
-      readFile: (target) =>
-        fs
-          .readFile(target)
-          .pipe(
-            Effect.tap((content) =>
-              Effect.sync(() => reads++).pipe(Effect.andThen(Effect.suspend(() => afterRead(target, content)))),
+    const current = yield* Environment.Service
+    return Environment.Service.of({
+      ...current,
+      files: {
+        ...current.files,
+        read: (target, range) =>
+          current.files
+            .read(target, range)
+            .pipe(
+              Effect.tap((result) =>
+                Effect.sync(() => reads++).pipe(Effect.andThen(Effect.suspend(() => afterRead(target, result.bytes)))),
+              ),
             ),
-          ),
-      writeWithDirs: (target, content, mode) =>
-        Effect.sync(() => writes.push(target)).pipe(Effect.andThen(fs.writeWithDirs(target, content, mode))),
-      writeFile: (target, content, options) =>
-        Effect.sync(() => writes.push(target)).pipe(Effect.andThen(fs.writeFile(target, content, options))),
-      writeFileString: (target, content, options) =>
-        Effect.sync(() => writes.push(target)).pipe(Effect.andThen(fs.writeFileString(target, content, options))),
+        write: (target, content) =>
+          Effect.sync(() => writes.push(target)).pipe(Effect.andThen(current.files.write(target, content))),
+      },
     })
   }),
-).pipe(Layer.provide(LayerNode.compile(FSUtil.node)))
+).pipe(Layer.provide(LayerNode.compile(Environment.node)))
 
 const withTool = <A, E, R>(directory: string, body: (registry: Tool.Interface) => Effect.Effect<A, E, R>) => {
   const activeLocation = Layer.succeed(
@@ -106,15 +113,9 @@ const withTool = <A, E, R>(directory: string, body: (registry: Tool.Interface) =
   }).pipe(
     Effect.provide(
       AppNodeBuilder.build(
-        LayerNode.group([
-          Tool.node,
-          Tool.node,
-          LocationMutation.node,
-          FileMutation.node,
-          editToolNode,
-        ]),
+        LayerNode.group([Tool.node, Tool.node, LocationMutation.node, FileMutation.node, editToolNode]),
         [
-          [FSUtil.node, filesystem],
+          [Environment.node, environment],
           [Location.node, activeLocation],
           [Formatter.node, formatter],
           [Permission.node, permission],
@@ -471,10 +472,7 @@ describe("EditTool", () => {
             withTool(tmp.path, (registry) =>
               Effect.gen(function* () {
                 expect(
-                  yield* executeTool(
-                    registry,
-                    call({ path: "missing.ts", oldString: "before", newString: "after" }),
-                  ),
+                  yield* executeTool(registry, call({ path: "missing.ts", oldString: "before", newString: "after" })),
                 ).toEqual({
                   status: "error",
                   error: { type: "tool.execution", message: "File not found: missing.ts" },
@@ -645,6 +643,43 @@ describe("EditTool", () => {
     ),
   )
 
+  it.live("serializes concurrent edit transactions", () =>
+    Effect.acquireUseRelease(
+      Effect.promise(() => tmpdir()),
+      (tmp) => {
+        reset()
+        const target = path.join(tmp.path, "concurrent.txt")
+        afterRead = () => (reads === 1 ? Effect.sleep("50 millis") : Effect.void)
+        return Effect.promise(() => fs.writeFile(target, "one\ntwo\n")).pipe(
+          Effect.andThen(
+            withTool(tmp.path, (registry) =>
+              Effect.all(
+                [
+                  executeTool(
+                    registry,
+                    call({ path: "concurrent.txt", oldString: "one", newString: "ONE" }, "call-edit-one"),
+                  ),
+                  executeTool(
+                    registry,
+                    call({ path: "concurrent.txt", oldString: "two", newString: "TWO" }, "call-edit-two"),
+                  ),
+                ],
+                { concurrency: "unbounded" },
+              ),
+            ),
+          ),
+          Effect.andThen((results) =>
+            Effect.gen(function* () {
+              expect(results.map((result) => result.status)).toEqual(["completed", "completed"])
+              expect(yield* Effect.promise(() => fs.readFile(target, "utf8"))).toBe("ONE\nTWO\n")
+            }),
+          ),
+        )
+      },
+      (tmp) => Effect.promise(() => tmp[Symbol.asyncDispose]()),
+    ),
+  )
+
   it.live("applies the edit when content changes after matching", () =>
     Effect.acquireUseRelease(
       Effect.promise(() => tmpdir()),

packages/core/test/tool-patch.test.ts

@@ -2,11 +2,12 @@ import fs from "fs/promises"
 import path from "path"
 import { describe, expect } from "bun:test"
 import { Effect, Exit, Layer, Schema } from "effect"
-import { systemError } from "effect/PlatformError"
 import { AppNodeBuilder } from "@opencode-ai/core/effect/app-node-builder"
 import { LayerNode } from "@opencode-ai/util/effect/layer-node"
+import { Environment } from "@opencode-ai/core/environment"
 import { FSUtil } from "@opencode-ai/util/fs-util"
 import { Formatter } from "@opencode-ai/core/formatter"
+import { FileMutation } from "@opencode-ai/core/file-mutation"
 import { Location } from "@opencode-ai/core/location"
 import { Permission } from "@opencode-ai/core/permission"
 import { AbsolutePath } from "@opencode-ai/core/schema"
@@ -22,7 +23,7 @@ import { toolIdentity, executeTool, registerToolPlugin, toolDefinitions } from "
 const patchToolNode = makeLocationNode({
   name: "test/patch-tool-plugin",
   layer: Layer.effectDiscard(registerToolPlugin(PatchTool.Plugin)),
-  deps: [Tool.node, Formatter.node, FSUtil.node, Location.node, Permission.node],
+  deps: [Tool.node, FileMutation.node, Environment.node, Formatter.node, Location.node, Permission.node],
 })
 
 const sessionID = Session.ID.make("ses_patch_tool_test")
@@ -81,48 +82,33 @@ const reset = () => {
   formatFile = () => Effect.succeed(false)
 }
 
-const filesystem = Layer.effect(
-  FSUtil.Service,
+const environment = Layer.effect(
+  Environment.Service,
   Effect.gen(function* () {
-    const fs = yield* FSUtil.Service
-    return FSUtil.Service.of({
-      ...fs,
-      readFile: (target) =>
-        Effect.sync(() => {
-          if (!editApproved) readsBeforeEditApproval++
-        }).pipe(Effect.andThen(fs.readFile(target))),
-      remove: (target, options) => {
-        if (failRemoveTarget && path.basename(target) === failRemoveTarget) return Effect.die("forced remove failure")
-        if (failRemoveErrorTarget && path.basename(target) === failRemoveErrorTarget) {
-          return Effect.fail(
-            systemError({
-              _tag: "Unknown",
-              module: "FileSystem",
-              method: "remove",
-              description: "forced remove failure",
-              pathOrDescriptor: target,
-            }),
-          )
-        }
-        return fs.remove(target, options)
-      },
-      writeWithDirs: (target, content, mode) => {
-        if (failWriteTarget && path.basename(target) === failWriteTarget) {
-          return Effect.fail(
-            systemError({
-              _tag: "Unknown",
-              module: "FileSystem",
-              method: "writeWithDirs",
-              description: "forced write failure",
-              pathOrDescriptor: target,
-            }),
-          )
-        }
-        return fs.writeWithDirs(target, content, mode)
+    const current = yield* Environment.Service
+    return Environment.Service.of({
+      ...current,
+      files: {
+        ...current.files,
+        read: (target, range) =>
+          Effect.sync(() => {
+            if (!editApproved) readsBeforeEditApproval++
+          }).pipe(Effect.andThen(current.files.read(target, range))),
+        remove: (target) => {
+          if (failRemoveTarget && path.basename(target) === failRemoveTarget) return Effect.die("forced remove failure")
+          if (failRemoveErrorTarget && path.basename(target) === failRemoveErrorTarget)
+            return Effect.fail(new Environment.Failed({ path: target, cause: new Error("forced remove failure") }))
+          return current.files.remove(target)
+        },
+        write: (target, content) => {
+          if (failWriteTarget && path.basename(target) === failWriteTarget)
+            return Effect.fail(new Environment.Failed({ path: target, cause: new Error("forced write failure") }))
+          return current.files.write(target, content)
+        },
       },
     })
   }),
-).pipe(Layer.provide(LayerNode.compile(FSUtil.node)))
+).pipe(Layer.provide(LayerNode.compile(Environment.node)))
 
 const withTool = <A, E, R>(
   directory: string,
@@ -139,8 +125,8 @@ const withTool = <A, E, R>(
     return yield* body(yield* Tool.Service)
   }).pipe(
     Effect.provide(
-      AppNodeBuilder.build(LayerNode.group([Tool.node, patchToolNode]), [
-        [FSUtil.node, filesystem],
+      AppNodeBuilder.build(LayerNode.group([Tool.node, FileMutation.node, patchToolNode]), [
+        [Environment.node, environment],
         [Location.node, activeLocation],
         [Formatter.node, formatter],
         [Permission.node, permission],
@@ -262,6 +248,43 @@ describe("PatchTool", () => {
     ),
   )
 
+  it.live("serializes concurrent patch transactions", () =>
+    withTempTool((directory, registry) => {
+      const target = path.join(directory, "concurrent.txt")
+      afterEditApproval = () =>
+        assertions.filter((input) => input.action === "edit").length === 1 ? Effect.sleep("50 millis") : Effect.void
+      return Effect.promise(() => fs.writeFile(target, "one\ntwo\n")).pipe(
+        Effect.andThen(
+          Effect.all(
+            [
+              executeTool(
+                registry,
+                call(
+                  "*** Begin Patch\n*** Update File: concurrent.txt\n@@\n-one\n+ONE\n*** End Patch",
+                  "call-patch-one",
+                ),
+              ),
+              executeTool(
+                registry,
+                call(
+                  "*** Begin Patch\n*** Update File: concurrent.txt\n@@\n-two\n+TWO\n*** End Patch",
+                  "call-patch-two",
+                ),
+              ),
+            ],
+            { concurrency: "unbounded" },
+          ),
+        ),
+        Effect.andThen((results) =>
+          Effect.gen(function* () {
+            expect(results.map((result) => result.status)).toEqual(["completed", "completed"])
+            expect(yield* Effect.promise(() => fs.readFile(target, "utf8"))).toBe("ONE\nTWO\n")
+          }),
+        ),
+      )
+    }),
+  )
+
   it.live("returns file diffs for final formatted content", () =>
     withTempTool((directory, registry) => {
       const target = path.join(directory, "formatted.txt")

packages/core/test/tool-read-filesystem.test.ts

@@ -1,66 +1,65 @@
 import { describe, expect } from "bun:test"
 import fs from "fs/promises"
 import path from "path"
-import { Effect, FileSystem } from "effect"
+import { Environment } from "@opencode-ai/core/environment"
+import { AbsolutePath } from "@opencode-ai/core/schema"
+import { ReadToolFileSystem } from "@opencode-ai/core/tool/read-filesystem"
+import { CrossSpawnSpawner } from "@opencode-ai/util/cross-spawn-spawner"
 import { LayerNodePlatform } from "@opencode-ai/util/effect/app-node-platform"
 import { LayerNode } from "@opencode-ai/util/effect/layer-node"
-import { FSUtil } from "@opencode-ai/util/fs-util"
-import { ReadToolFileSystem } from "@opencode-ai/core/tool/read-filesystem"
+import { Effect, FileSystem } from "effect"
+import { ChildProcessSpawner } from "effect/unstable/process"
 import { testEffect } from "./lib/effect"
 
-const it = testEffect(LayerNode.compile(LayerNode.group([FSUtil.node, LayerNodePlatform.filesystem])))
+const it = testEffect(LayerNode.compile(LayerNode.group([CrossSpawnSpawner.node, LayerNodePlatform.filesystem])))
 const fixture = Effect.gen(function* () {
-  const fs = yield* FSUtil.Service
   const files = yield* FileSystem.FileSystem
+  const spawner = yield* ChildProcessSpawner.ChildProcessSpawner
   const directory = yield* files.makeTempDirectoryScoped()
-  return { fs, files, directory }
+  return { environment: Environment.makeFiles(Environment.makeLocalDriver(spawner)), files, directory }
 })
+const absolute = (value: string) => AbsolutePath.make(value)
 
 describe("ReadToolFileSystem", () => {
-  it.effect("fails with a typed filesystem error when a resolved file disappears", () =>
+  it.effect("preserves the environment not-found error", () =>
     Effect.gen(function* () {
-      const { fs, directory } = yield* fixture
+      const { environment, directory } = yield* fixture
       const file = path.join(directory, "missing.txt")
 
-      const error = yield* ReadToolFileSystem.read(fs, file, "missing.txt").pipe(Effect.flip)
+      const error = yield* ReadToolFileSystem.read(environment, absolute(file), "missing.txt").pipe(Effect.flip)
 
-      expect(error).toMatchObject({ _tag: "PlatformError" })
+      expect(error).toBeInstanceOf(Environment.NotFound)
     }),
   )
 
-  it.effect("fails when a file becomes the wrong path kind", () =>
+  it.effect("returns a listing when read reports a directory", () =>
     Effect.gen(function* () {
-      const { fs, directory } = yield* fixture
+      const { environment, files, directory } = yield* fixture
+      yield* files.makeDirectory(path.join(directory, "folder"))
+      yield* files.writeFileString(path.join(directory, "file.txt"), "hello")
 
-      const error = yield* ReadToolFileSystem.read(fs, directory, "folder").pipe(Effect.flip)
+      const result = yield* ReadToolFileSystem.read(environment, absolute(directory), "folder")
 
-      expect(error).toBeInstanceOf(ReadToolFileSystem.PathKindError)
-    }),
-  )
-
-  it.effect("fails with a typed filesystem error when directory listing fails", () =>
-    Effect.gen(function* () {
-      const { fs, files, directory } = yield* fixture
-      const file = path.join(directory, "file.txt")
-      yield* files.writeFileString(file, "hello")
-
-      const error = yield* ReadToolFileSystem.list(fs, file).pipe(Effect.flip)
-
-      expect(error).toBeInstanceOf(FSUtil.FileSystemError)
-      if (error instanceof FSUtil.FileSystemError) expect(error.method).toBe("readDirectoryEntries")
+      expect(result).toMatchObject({
+        type: "list-page",
+        entries: [
+          { path: `folder${path.sep}`, type: "directory" },
+          { path: "file.txt", type: "file" },
+        ],
+      })
     }),
   )
 
   it.effect("reads malformed UTF-8 lossily and still rejects null-byte binary content", () =>
     Effect.gen(function* () {
-      const { fs, files, directory } = yield* fixture
+      const { environment, files, directory } = yield* fixture
       const binary = path.join(directory, "archive.dat")
       const malformed = path.join(directory, "malformed.txt")
       yield* files.writeFile(binary, Uint8Array.of(0, 1, 2, 3))
       yield* files.writeFile(malformed, Uint8Array.of(0x68, 0x69, 0x80))
 
-      const binaryError = yield* ReadToolFileSystem.read(fs, binary, "archive.dat").pipe(Effect.flip)
-      const malformedResult = yield* ReadToolFileSystem.read(fs, malformed, "malformed.txt")
+      const binaryError = yield* ReadToolFileSystem.read(environment, absolute(binary), "archive.dat").pipe(Effect.flip)
+      const malformedResult = yield* ReadToolFileSystem.read(environment, absolute(malformed), "malformed.txt")
 
       expect(binaryError).toBeInstanceOf(ReadToolFileSystem.BinaryFileError)
       expect(binaryError.message).toBe("Cannot read binary file: archive.dat")
@@ -70,11 +69,11 @@ describe("ReadToolFileSystem", () => {
 
   it.effect("reads text despite a binary-associated extension", () =>
     Effect.gen(function* () {
-      const { fs, files, directory } = yield* fixture
+      const { environment, files, directory } = yield* fixture
       const file = path.join(directory, "notes.docx")
       yield* files.writeFileString(file, "plain text")
 
-      const result = yield* ReadToolFileSystem.read(fs, file, "notes.docx")
+      const result = yield* ReadToolFileSystem.read(environment, absolute(file), "notes.docx")
 
       expect(result).toMatchObject({ type: "file", content: "plain text", encoding: "utf8" })
     }),
@@ -83,15 +82,17 @@ describe("ReadToolFileSystem", () => {
   it.effect("lists unresolved symlinks, including broken and escaping links", () =>
     Effect.gen(function* () {
       if (process.platform === "win32") return
-      const { fs: service, files, directory } = yield* fixture
+      const { environment, files, directory } = yield* fixture
       const outside = yield* files.makeTempDirectoryScoped()
       yield* files.makeDirectory(path.join(directory, "folder"))
       yield* files.writeFileString(path.join(directory, "file.txt"), "hello")
       yield* Effect.promise(() => fs.symlink(path.join(outside, "target.txt"), path.join(directory, "escape")))
       yield* Effect.promise(() => fs.symlink(path.join(directory, "missing.txt"), path.join(directory, "broken")))
 
-      const result = yield* ReadToolFileSystem.list(service, directory)
+      const result = yield* ReadToolFileSystem.read(environment, absolute(directory), "folder")
 
+      expect(result.type).toBe("list-page")
+      if (result.type !== "list-page") return
       expect(result.entries.map((entry) => ({ ...entry, path: String(entry.path) }))).toEqual([
         { path: `folder${path.sep}`, type: "directory" },
         { path: "broken", type: "symlink" },
@@ -101,45 +102,154 @@ describe("ReadToolFileSystem", () => {
     }),
   )
 
+  it.effect("reads a symlinked directory as a listing", () =>
+    Effect.gen(function* () {
+      if (process.platform === "win32") return
+      const { environment, files, directory } = yield* fixture
+      const target = path.join(directory, "target")
+      const link = path.join(directory, "link")
+      yield* files.makeDirectory(target)
+      yield* files.writeFileString(path.join(target, "file.txt"), "hello")
+      yield* Effect.promise(() => fs.symlink(target, link))
+
+      const result = yield* ReadToolFileSystem.read(environment, absolute(link), "link")
+
+      expect(result).toMatchObject({
+        type: "list-page",
+        entries: [{ path: "file.txt", type: "file" }],
+      })
+    }),
+  )
+
   it.effect("reports out-of-range pagination as a typed error", () =>
     Effect.gen(function* () {
-      const { fs, files, directory } = yield* fixture
+      const { environment, files, directory } = yield* fixture
       const file = path.join(directory, "short.txt")
       yield* files.writeFileString(file, "one\n")
 
-      const error = yield* ReadToolFileSystem.read(fs, file, "short.txt", { offset: 2 }).pipe(Effect.flip)
+      const error = yield* ReadToolFileSystem.read(environment, absolute(file), "short.txt", { offset: 2 }).pipe(
+        Effect.flip,
+      )
 
       expect(error).toBeInstanceOf(ReadToolFileSystem.OffsetOutOfRangeError)
       expect(error.message).toBe("Offset 2 is out of range")
     }),
   )
 
-  it.effect("stops reading after the requested page is complete", () =>
+  it.effect("pages text with one-based offsets", () =>
     Effect.gen(function* () {
-      const { fs, files, directory } = yield* fixture
-      const prefix = new TextEncoder().encode("one\n")
-      for (const [name, trailing] of [
-        ["malformed.txt", 0x80],
-        ["nul.txt", 0],
-      ] as const) {
-        const file = path.join(directory, name)
-        yield* files.writeFile(file, Uint8Array.from([...prefix, trailing]))
+      const { environment, files, directory } = yield* fixture
+      const file = path.join(directory, "lines.txt")
+      yield* files.writeFileString(file, "one\r\ntwo\nthree")
 
-        const result = yield* ReadToolFileSystem.read(fs, file, name, { limit: 1 })
+      const result = yield* ReadToolFileSystem.read(environment, absolute(file), "lines.txt", {
+        offset: 2,
+        limit: 1,
+      })
 
-        expect(result).toMatchObject({ type: "text-page", content: "one", truncated: true, next: 2 })
+      expect(result).toMatchObject({ type: "text-page", content: "two", offset: 2, truncated: true, next: 3 })
+    }),
+  )
+
+  it.effect("truncates long lines", () =>
+    Effect.gen(function* () {
+      const { environment, files, directory } = yield* fixture
+      const file = path.join(directory, "long.txt")
+      yield* files.writeFileString(file, "a".repeat(2_001))
+
+      const result = yield* ReadToolFileSystem.read(environment, absolute(file), "long.txt", { limit: 1 })
+
+      expect(result).toMatchObject({
+        type: "text-page",
+        content: `${"a".repeat(2_000)}... (line truncated to 2000 chars)`,
+        truncated: false,
+      })
+    }),
+  )
+
+  it.effect("enforces line and byte budgets with continuation offsets", () =>
+    Effect.gen(function* () {
+      const { environment, files, directory } = yield* fixture
+      const linesFile = path.join(directory, "many-lines.txt")
+      const bytesFile = path.join(directory, "many-bytes.txt")
+      yield* files.writeFileString(linesFile, Array.from({ length: 2_001 }, (_, index) => String(index)).join("\n"))
+      yield* files.writeFileString(bytesFile, Array.from({ length: 200 }, () => "a".repeat(2_000)).join("\n"))
+      const ranges: Array<{ readonly offset: number; readonly length: number } | undefined> = []
+      const tracked = {
+        ...environment,
+        read: (path: string, range?: { readonly offset: number; readonly length: number }) =>
+          Effect.sync(() => ranges.push(range)).pipe(Effect.andThen(environment.read(path, range))),
       }
+
+      const lines = yield* ReadToolFileSystem.read(environment, absolute(linesFile), "many-lines.txt", { limit: 2_000 })
+      const bytes = yield* ReadToolFileSystem.read(tracked, absolute(bytesFile), "many-bytes.txt", {})
+
+      expect(lines).toMatchObject({ type: "text-page", truncated: true, next: 2_001 })
+      expect(lines.type === "text-page" ? lines.content.split("\n") : []).toHaveLength(2_000)
+      expect(bytes).toMatchObject({ type: "text-page", truncated: true, next: 26 })
+      expect(bytes.type === "text-page" ? Buffer.byteLength(bytes.content) : Infinity).toBeLessThanOrEqual(
+        ReadToolFileSystem.MAX_READ_BYTES,
+      )
+      expect(ranges).toEqual([{ offset: 0, length: 256 * 1024 }])
+    }),
+  )
+
+  it.effect("sorts and pages directory entries", () =>
+    Effect.gen(function* () {
+      const { environment, files, directory } = yield* fixture
+      yield* files.makeDirectory(path.join(directory, "z"))
+      yield* files.makeDirectory(path.join(directory, "a"))
+      yield* files.writeFileString(path.join(directory, "b.txt"), "")
+
+      const result = yield* ReadToolFileSystem.read(environment, absolute(directory), "folder", {
+        offset: 2,
+        limit: 1,
+      })
+
+      expect(result).toMatchObject({
+        type: "list-page",
+        entries: [{ path: `z${path.sep}`, type: "directory" }],
+        truncated: true,
+        next: 3,
+      })
+    }),
+  )
+
+  it.effect("stops checking for null bytes after the requested page", () =>
+    Effect.gen(function* () {
+      const { environment, files, directory } = yield* fixture
+      const file = path.join(directory, "nul.txt")
+      yield* files.writeFile(file, Uint8Array.from([...new TextEncoder().encode("one\n"), 0]))
+
+      const result = yield* ReadToolFileSystem.read(environment, absolute(file), "nul.txt", { limit: 1 })
+
+      expect(result).toMatchObject({ type: "text-page", content: "one", truncated: true, next: 2 })
+    }),
+  )
+
+  it.effect("reads page two after fetching more than the first 256KB range", () =>
+    Effect.gen(function* () {
+      const { environment, files, directory } = yield* fixture
+      const file = path.join(directory, "large.txt")
+      yield* files.writeFileString(file, `${"a".repeat(300 * 1024)}\nsecond\n`)
+
+      const result = yield* ReadToolFileSystem.read(environment, absolute(file), "large.txt", {
+        offset: 2,
+        limit: 1,
+      })
+
+      expect(result).toMatchObject({ type: "text-page", content: "second", offset: 2, truncated: false })
     }),
   )
 
   it.effect("preserves the media ingestion limit message", () =>
     Effect.gen(function* () {
-      const { fs, files, directory } = yield* fixture
+      const { environment, files, directory } = yield* fixture
       const file = path.join(directory, "oversized.png")
       yield* files.writeFile(file, Uint8Array.of(0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a))
       yield* files.truncate(file, ReadToolFileSystem.MAX_MEDIA_INGEST_BYTES + 1)
 
-      const error = yield* ReadToolFileSystem.read(fs, file, "oversized.png").pipe(Effect.flip)
+      const error = yield* ReadToolFileSystem.read(environment, absolute(file), "oversized.png").pipe(Effect.flip)
 
       expect(error).toBeInstanceOf(ReadToolFileSystem.MediaIngestLimitError)
       expect(error.message).toBe(
@@ -150,11 +260,11 @@ describe("ReadToolFileSystem", () => {
 
   it.effect("reads PDFs as bounded media", () =>
     Effect.gen(function* () {
-      const { fs, files, directory } = yield* fixture
+      const { environment, files, directory } = yield* fixture
       const file = path.join(directory, "document.pdf")
       yield* files.writeFileString(file, "%PDF-1.7\ncontent")
 
-      const result = yield* ReadToolFileSystem.read(fs, file, "document.pdf")
+      const result = yield* ReadToolFileSystem.read(environment, absolute(file), "document.pdf")
 
       expect(result).toMatchObject({
         type: "file",

packages/core/test/tool-read.test.ts

@@ -1,6 +1,6 @@
 import { beforeEach, describe, expect } from "bun:test"
 import path from "path"
-import { Effect, Exit, Layer, PlatformError, Stream } from "effect"
+import { Effect, Exit, Layer, Stream } from "effect"
 import { Config } from "@opencode-ai/core/config"
 import { Document, Info } from "@opencode-ai/schema/config"
 import { ConfigMedia } from "@opencode-ai/schema/config/media"
@@ -21,6 +21,7 @@ import { ReadTool } from "@opencode-ai/core/tool/plugin/read"
 import { ReadToolFileSystem } from "@opencode-ai/core/tool/read-filesystem"
 import { makeLocationNode } from "@opencode-ai/util/effect/app-node"
 import { SessionInstructions } from "@opencode-ai/core/session/instructions"
+import { Environment } from "@opencode-ai/core/environment"
 import { testEffect } from "./lib/effect"
 import { toolIdentity, executeTool, registerToolPlugin, toolDefinitions } from "./lib/tool"
 
@@ -42,24 +43,13 @@ const readToolNode = makeLocationNode({
 const assertions: Permission.AssertInput[] = []
 const missingPath = "__missing_read_target__.txt"
 const missingAbsolutePath = path.join(process.cwd(), missingPath)
-const notFound = (target: string) =>
-  PlatformError.systemError({
-    _tag: "NotFound",
-    module: "FileSystem",
-    method: "stat",
-    pathOrDescriptor: target,
-  })
 const readCalls: {
   input: AbsolutePath
   page: ReadToolFileSystem.PageInput
 }[] = []
-const listCalls: ReadToolFileSystem.PageInput[] = []
-let listResult = new ReadToolFileSystem.ListPage({ type: "list-page", entries: [], truncated: false })
-let resolvedType: "file" | "directory" = "file"
 let resolveFailure: unknown
-let inspectFailure: ReadToolFileSystem.InspectError | undefined
 let directoryEntries: string[] = []
-let readResult: ReadToolFileSystem.FileContent | ReadToolFileSystem.TextPage = {
+let readResult: ReadToolFileSystem.FileContent | ReadToolFileSystem.TextPage | ReadToolFileSystem.ListPage = {
   type: "file",
   uri: "file:///README.md",
   name: "README.md",
@@ -71,22 +61,12 @@ let readFailure: ReadToolFileSystem.ReadError | undefined
 const reader = Layer.succeed(
   ReadToolFileSystem.Service,
   ReadToolFileSystem.Service.of({
-    inspect: () =>
-      resolveFailure !== undefined
-        ? Effect.die(resolveFailure)
-        : inspectFailure !== undefined
-          ? Effect.fail(inspectFailure)
-          : Effect.succeed(resolvedType),
     read: (input, _resource, page = {}) => {
       readCalls.push({ input, page })
+      if (resolveFailure !== undefined) return Effect.die(resolveFailure)
       if (readFailure !== undefined) return Effect.fail(readFailure)
       return Effect.succeed(readResult)
     },
-    list: (_path, input = {}) =>
-      Effect.sync(() => {
-        listCalls.push(input)
-        return listResult
-      }),
   }),
 )
 let allow = true
@@ -125,17 +105,6 @@ const testFileSystem = Layer.effect(
       FSUtil.Service.of({
         ...fs,
         readDirectory: () => Effect.succeed(directoryEntries),
-        realPath: (path) =>
-          path === missingAbsolutePath
-            ? Effect.fail(
-                PlatformError.systemError({
-                  _tag: "NotFound",
-                  module: "FileSystem",
-                  method: "realPath",
-                  pathOrDescriptor: path,
-                }),
-              )
-            : Effect.succeed(path),
       }),
     ),
   ),
@@ -195,11 +164,8 @@ describe("ReadTool", () => {
   beforeEach(() => {
     assertions.length = 0
     readCalls.length = 0
-    listCalls.length = 0
     allow = true
-    resolvedType = "file"
     resolveFailure = undefined
-    inspectFailure = undefined
     directoryEntries = []
     readResult = {
       type: "file",
@@ -210,7 +176,6 @@ describe("ReadTool", () => {
       mime: "text/plain",
     }
     readFailure = undefined
-    listResult = new ReadToolFileSystem.ListPage({ type: "list-page", entries: [], truncated: false })
   })
 
   it.effect("registers, authorizes, and reads through the location filesystem", () =>
@@ -672,7 +637,7 @@ describe("ReadTool", () => {
 
   it.effect("returns missing paths as model-visible tool failures", () =>
     Effect.gen(function* () {
-      inspectFailure = notFound(missingAbsolutePath)
+      readFailure = new Environment.NotFound({ path: missingAbsolutePath })
       directoryEntries = [
         "__missing_read_target__.txt.bak",
         "copy___missing_read_target__.txt",
@@ -696,14 +661,18 @@ describe("ReadTool", () => {
         },
       })
       expect(assertions).toMatchObject([{ sessionID, action: "read", resources: [missingPath], save: ["*"] }])
-      expect(readCalls).toEqual([])
+      expect(readCalls).toEqual([
+        {
+          input: AbsolutePath.make(missingAbsolutePath),
+          page: { offset: undefined, limit: undefined },
+        },
+      ])
     }),
   )
 
   it.effect("lists a bounded directory page through read", () =>
     Effect.gen(function* () {
-      resolvedType = "directory"
-      listResult = new ReadToolFileSystem.ListPage({
+      readResult = new ReadToolFileSystem.ListPage({
         type: "list-page",
         entries: [
           FileSystem.Entry.make({ path: RelativePath.make("components/"), type: "directory" }),
@@ -726,7 +695,7 @@ describe("ReadTool", () => {
       })
       expect(result).toMatchObject({
         status: "completed",
-        output: { entries: listResult.entries, truncated: true, next: 4 },
+        output: { entries: readResult.entries, truncated: true, next: 4 },
       })
       if (result.status !== "completed") return
       expect(result.metadata).toEqual({ truncated: true })
@@ -737,14 +706,15 @@ describe("ReadTool", () => {
         },
       ])
       expect(assertions).toMatchObject([{ sessionID, action: "read", resources: ["src"], save: ["*"] }])
-      expect(listCalls).toEqual([{ offset: 2, limit: 10 }])
+      expect(readCalls).toEqual([
+        { input: AbsolutePath.make(path.join(process.cwd(), "src")), page: { offset: 2, limit: 10 } },
+      ])
     }),
   )
 
   it.effect("does not list a directory when permission is denied", () =>
     Effect.gen(function* () {
       allow = false
-      resolvedType = "directory"
       const registry = yield* Tool.Service
 
       expect(
@@ -754,7 +724,7 @@ describe("ReadTool", () => {
           call: { type: "tool-call", id: "call-read-directory-denied", name: "read", input: { path: "src" } },
         }),
       ).toEqual({ status: "error", error: { type: "permission.rejected", message: "Permission denied: read" } })
-      expect(listCalls).toEqual([])
+      expect(readCalls).toEqual([])
     }),
   )
 
@@ -773,7 +743,12 @@ describe("ReadTool", () => {
         ),
       ).toBe(true)
 
-      expect(readCalls).toEqual([])
+      expect(readCalls).toEqual([
+        {
+          input: AbsolutePath.make(path.join(process.cwd(), "missing.txt")),
+          page: { offset: undefined, limit: undefined },
+        },
+      ])
     }),
   )
 

packages/core/test/tool-search.test.ts

@@ -5,8 +5,8 @@ import { Effect, Layer } from "effect"
 import { AppNodeBuilder } from "@opencode-ai/core/effect/app-node-builder"
 import { makeLocationNode } from "@opencode-ai/util/effect/app-node"
 import { LayerNode } from "@opencode-ai/util/effect/layer-node"
+import { Environment } from "@opencode-ai/core/environment"
 import { FileSystem } from "@opencode-ai/core/filesystem"
-import { FSUtil } from "@opencode-ai/util/fs-util"
 import { Location } from "@opencode-ai/core/location"
 import { LocationMutation } from "@opencode-ai/core/location-mutation"
 import { Permission } from "@opencode-ai/core/permission"
@@ -24,19 +24,12 @@ import { executeTool, registerToolPlugin, toolIdentity } from "./lib/tool"
 const globToolNode = makeLocationNode({
   name: "test/glob-tool-plugin",
   layer: Layer.effectDiscard(registerToolPlugin(GlobTool.Plugin)),
-  deps: [
-    Tool.node,
-    FSUtil.node,
-    Ripgrep.node,
-    Location.node,
-    LocationMutation.node,
-    Permission.node,
-  ],
+  deps: [Tool.node, Environment.node, Ripgrep.node, Location.node, LocationMutation.node, Permission.node],
 })
 const grepToolNode = makeLocationNode({
   name: "test/grep-tool-plugin",
   layer: Layer.effectDiscard(registerToolPlugin(GrepTool.Plugin)),
-  deps: [Tool.node, FSUtil.node, Ripgrep.node, Location.node, LocationMutation.node, Permission.node],
+  deps: [Tool.node, Environment.node, Ripgrep.node, Location.node, LocationMutation.node, Permission.node],
 })
 const sessionID = Session.ID.make("ses_search_tool_test")
 
@@ -186,9 +179,7 @@ describe("search tools", () => {
       Effect.promise(() => tmpdir()),
       (tmp) =>
         Effect.promise(() => fs.writeFile(path.join(tmp.path, "file.txt"), "haystack\n")).pipe(
-          Effect.andThen(
-            withTools(tmp.path, (registry) => executeTool(registry, call("grep", { pattern: "needle" }))),
-          ),
+          Effect.andThen(withTools(tmp.path, (registry) => executeTool(registry, call("grep", { pattern: "needle" })))),
           Effect.tap((result) =>
             Effect.sync(() => {
               expect(result).toMatchObject({
@@ -297,9 +288,7 @@ describe("search tools", () => {
       (tmp) =>
         Effect.promise(() => fs.writeFile(path.join(tmp.path, "file.txt"), "content\n")).pipe(
           Effect.andThen(
-            withTools(tmp.path, (registry) =>
-              executeTool(registry, call("glob", { path: "file.txt", pattern: "*" })),
-            ),
+            withTools(tmp.path, (registry) => executeTool(registry, call("glob", { path: "file.txt", pattern: "*" }))),
           ),
           Effect.tap((result) =>
             Effect.sync(() => {
@@ -331,9 +320,7 @@ describe("search tools", () => {
             Effect.sync(() => {
               expect(result.status).toBe("completed")
               expect(assertions.map((input) => input.action)).toEqual(["external_directory", "glob"])
-              expect(assertions[0]?.resources).toEqual([
-                path.join(outside.path, "*").replaceAll("\\", "/"),
-              ])
+              expect(assertions[0]?.resources).toEqual([path.join(outside.path, "*").replaceAll("\\", "/")])
             }),
           ),
         )

packages/core/test/tool-shell.test.ts

@@ -524,7 +524,8 @@ describe("ShellTool", () => {
           const content = settled.content?.[0]
           if (!content || content.type !== "text") throw new Error("Expected text content")
           expect(content.text).not.toContain("one")
-          expect(content.text).toStartWith("two\nthree")
+          // Windows shells emit CRLF; the assertion targets line limits, not line endings.
+          expect(content.text.replaceAll("\r\n", "\n")).toStartWith("two\nthree")
           expect(content.text).toContain("output truncated; full output saved to:")
         })
       },

packages/core/test/tool-write.test.ts

@@ -6,7 +6,7 @@ import { FileMutation } from "@opencode-ai/core/file-mutation"
 import { Formatter } from "@opencode-ai/core/formatter"
 import { AppNodeBuilder } from "@opencode-ai/core/effect/app-node-builder"
 import { LayerNode } from "@opencode-ai/util/effect/layer-node"
-import { FSUtil } from "@opencode-ai/util/fs-util"
+import { Environment } from "@opencode-ai/core/environment"
 import { Location } from "@opencode-ai/core/location"
 import { LocationMutation } from "@opencode-ai/core/location-mutation"
 import { Permission } from "@opencode-ai/core/permission"
@@ -23,7 +23,7 @@ import { toolIdentity, executeTool, registerToolPlugin, toolDefinitions } from "
 const writeToolNode = makeLocationNode({
   name: "test/write-tool-plugin",
   layer: Layer.effectDiscard(registerToolPlugin(WriteTool.Plugin)),
-  deps: [Tool.node, LocationMutation.node, FileMutation.node, Formatter.node, FSUtil.node, Permission.node],
+  deps: [Tool.node, LocationMutation.node, FileMutation.node, Environment.node, Formatter.node, Permission.node],
 })
 
 const sessionID = Session.ID.make("ses_write_tool_test")
@@ -68,17 +68,20 @@ const reset = () => {
   denyAction = undefined
 }
 
-const filesystem = Layer.effect(
-  FSUtil.Service,
+const environment = Layer.effect(
+  Environment.Service,
   Effect.gen(function* () {
-    const fs = yield* FSUtil.Service
-    return FSUtil.Service.of({
-      ...fs,
-      writeWithDirs: (target, content, mode) =>
-        Effect.sync(() => writes.push(target)).pipe(Effect.andThen(fs.writeWithDirs(target, content, mode))),
+    const current = yield* Environment.Service
+    return Environment.Service.of({
+      ...current,
+      files: {
+        ...current.files,
+        write: (target, content) =>
+          Effect.sync(() => writes.push(target)).pipe(Effect.andThen(current.files.write(target, content))),
+      },
     })
   }),
-).pipe(Layer.provide(LayerNode.compile(FSUtil.node)))
+).pipe(Layer.provide(LayerNode.compile(Environment.node)))
 
 const withTool = <A, E, R>(directory: string, body: (registry: Tool.Interface) => Effect.Effect<A, E, R>) => {
   const activeLocation = Layer.succeed(
@@ -92,7 +95,7 @@ const withTool = <A, E, R>(directory: string, body: (registry: Tool.Interface) =
       AppNodeBuilder.build(
         LayerNode.group([Tool.node, Tool.node, LocationMutation.node, FileMutation.node, writeToolNode]),
         [
-          [FSUtil.node, filesystem],
+          [Environment.node, environment],
           [Location.node, activeLocation],
           [Formatter.node, formatter],
           [Permission.node, permission],

packages/merman/package.json

@@ -0,0 +1,26 @@
+{
+  "$schema": "https://json.schemastore.org/package.json",
+  "name": "@opencode-ai/merman",
+  "version": "0.0.0",
+  "private": true,
+  "type": "module",
+  "exports": {
+    ".": "./src/index.ts",
+    "./markdown": "./src/markdown.ts",
+    "./plugin": "./src/plugin.ts"
+  },
+  "scripts": {
+    "test": "bun test --timeout 30000 --only-failures",
+    "typecheck": "tsgo --noEmit"
+  },
+  "dependencies": {
+    "@opencode-ai/plugin": "workspace:*",
+    "@opentui/core": "catalog:",
+    "string-width": "catalog:"
+  },
+  "devDependencies": {
+    "@tsconfig/bun": "catalog:",
+    "@types/bun": "catalog:",
+    "@typescript/native-preview": "catalog:"
+  }
+}

packages/merman/src/core/adapter/diagram-renderable.ts

@@ -0,0 +1,97 @@
+import {
+  TextBufferRenderable,
+  type ColorInput,
+  type RenderContext,
+  type RGBA,
+  type StyledText,
+  type TextBufferOptions,
+} from "@opentui/core"
+import type { DiagramCanvas, DiagramCanvasTextOptions } from "../canvas.js"
+import { setDiagramRenderableColor } from "./renderable-color.js"
+import { DiagramRenderablePipeline } from "./renderable-pipeline.js"
+
+interface DiagramRenderableOptions<Diagram, Grid extends DiagramCanvas<any, any>> {
+  parse: () => Diagram
+  draw: (diagram: Diagram) => Grid
+  publish: (grid: Grid) => StyledText
+  measure?: DiagramCanvasTextOptions
+}
+
+export abstract class DiagramRenderable<Diagram, Grid extends DiagramCanvas<any, any>> extends TextBufferRenderable {
+  private _content: string
+  private _renderedWidth = 0
+  private _renderedHeight = 0
+  private _pipeline?: DiagramRenderablePipeline<Diagram, Grid>
+
+  protected constructor(ctx: RenderContext, options: TextBufferOptions & { content?: string }) {
+    super(ctx, { ...options, wrapMode: options.wrapMode ?? "none" })
+    this._content = options.content ?? ""
+  }
+
+  protected initializeDiagram(options: DiagramRenderableOptions<Diagram, Grid>): void {
+    this._pipeline = new DiagramRenderablePipeline({
+      parse: options.parse,
+      draw: options.draw,
+      didDraw: (grid) => {
+        const size = grid.getTextSize(options.measure)
+        this._renderedWidth = size.width
+        this._renderedHeight = size.height
+      },
+      publish: (grid) => {
+        this.textBuffer.setStyledText(options.publish(grid))
+        this.updateTextInfo()
+      },
+    })
+    this._pipeline.invalidateParsedDiagram()
+  }
+
+  get content(): string {
+    return this._content
+  }
+
+  set content(value: string) {
+    if (this._content === value) return
+    this._content = value
+    this.contentChanged()
+    this.pipeline.invalidateParsedDiagram()
+  }
+
+  get renderedWidth(): number {
+    return this._renderedWidth
+  }
+
+  get renderedHeight(): number {
+    return this._renderedHeight
+  }
+
+  batchUpdate(update: () => void): void {
+    this.pipeline.batchUpdate(update)
+  }
+
+  protected contentChanged(): void {}
+
+  protected parsedDiagram(): Diagram {
+    return this.pipeline.diagram()
+  }
+
+  protected invalidateGrid(): void {
+    this.pipeline.invalidateGrid()
+  }
+
+  protected invalidateStyle(): void {
+    this.pipeline.invalidateStyle()
+  }
+
+  protected setColor(
+    current: RGBA | undefined,
+    value: ColorInput | undefined,
+    assign: (color: RGBA | undefined) => void,
+  ): void {
+    setDiagramRenderableColor(current, value, assign, () => this.invalidateStyle())
+  }
+
+  private get pipeline(): DiagramRenderablePipeline<Diagram, Grid> {
+    if (!this._pipeline) throw new Error("Diagram renderable was not initialized")
+    return this._pipeline
+  }
+}

packages/merman/src/core/adapter/renderable-color.ts

@@ -0,0 +1,18 @@
+import { parseColor, type ColorInput, type RGBA } from "@opentui/core"
+import { colorsEqual } from "../color/style.js"
+
+export function parseDiagramRenderableColor(value: ColorInput | undefined): RGBA | undefined {
+  return value ? parseColor(value) : undefined
+}
+
+export function setDiagramRenderableColor(
+  current: RGBA | undefined,
+  value: ColorInput | undefined,
+  assign: (color: RGBA | undefined) => void,
+  invalidate: () => void,
+): void {
+  const next = parseDiagramRenderableColor(value)
+  if (colorsEqual(current, next)) return
+  assign(next)
+  invalidate()
+}

packages/merman/src/core/adapter/renderable-pipeline.test.ts

@@ -0,0 +1,48 @@
+import { describe, expect, test } from "bun:test"
+import { DiagramRenderablePipeline } from "./renderable-pipeline.js"
+
+describe("DiagramRenderablePipeline", () => {
+  test("caches the parsed diagram and grid across style repaints", () => {
+    let parseCount = 0
+    let drawCount = 0
+    let publishCount = 0
+    const pipeline = new DiagramRenderablePipeline({
+      parse: () => ({ version: ++parseCount }),
+      draw: (diagram) => ({ version: diagram.version, draw: ++drawCount }),
+      publish: () => {
+        publishCount += 1
+      },
+    })
+
+    pipeline.invalidateParsedDiagram()
+    pipeline.invalidateStyle()
+    pipeline.invalidateGrid()
+
+    expect({ parseCount, drawCount, publishCount }).toEqual({ parseCount: 1, drawCount: 2, publishCount: 3 })
+  })
+
+  test("reparses source changes and coalesces nested invalidations", () => {
+    const events: string[] = []
+    const pipeline = new DiagramRenderablePipeline({
+      parse: () => {
+        events.push("parse")
+        return {}
+      },
+      draw: (diagram) => {
+        events.push("draw")
+        return diagram
+      },
+      publish: () => events.push("publish"),
+    })
+
+    pipeline.invalidateParsedDiagram()
+    events.length = 0
+    pipeline.batchUpdate(() => {
+      pipeline.invalidateStyle()
+      pipeline.batchUpdate(() => pipeline.invalidateGrid())
+      pipeline.invalidateParsedDiagram()
+    })
+
+    expect(events).toEqual(["parse", "draw", "publish"])
+  })
+})

packages/merman/src/core/adapter/renderable-pipeline.ts

@@ -0,0 +1,68 @@
+export interface DiagramRenderablePipelineOptions<Diagram, Grid> {
+  parse: () => Diagram
+  draw: (diagram: Diagram) => Grid
+  publish: (grid: Grid) => void
+  didDraw?: (grid: Grid) => void
+}
+
+type DiagramRenderableInvalidation = "grid" | "style"
+
+export class DiagramRenderablePipeline<Diagram, Grid> {
+  private _diagram?: Diagram
+  private _grid?: Grid
+  private _batchDepth = 0
+  private _pending?: DiagramRenderableInvalidation
+
+  constructor(private readonly options: DiagramRenderablePipelineOptions<Diagram, Grid>) {}
+
+  diagram(): Diagram {
+    this._diagram ??= this.options.parse()
+    return this._diagram
+  }
+
+  batchUpdate(update: () => void): void {
+    this._batchDepth += 1
+    try {
+      update()
+    } finally {
+      this._batchDepth -= 1
+      if (this._batchDepth === 0 && this._pending) {
+        const pending = this._pending
+        this._pending = undefined
+        this.render(pending)
+      }
+    }
+  }
+
+  invalidateParsedDiagram(): void {
+    this._diagram = undefined
+    this.invalidateGrid()
+  }
+
+  invalidateGrid(): void {
+    this._grid = undefined
+    this.invalidate("grid")
+  }
+
+  invalidateStyle(): void {
+    this.invalidate("style")
+  }
+
+  private invalidate(level: DiagramRenderableInvalidation): void {
+    if (this._batchDepth > 0) {
+      if (level === "grid" || !this._pending) this._pending = level
+      return
+    }
+    this.render(level)
+  }
+
+  private render(level: DiagramRenderableInvalidation): void {
+    let grid = this._grid
+    if (level === "grid" || !grid) {
+      grid = this.options.draw(this.diagram())
+      this._grid = grid
+      this.options.didDraw?.(grid)
+    }
+    this.options.publish(grid)
+  }
+}

packages/merman/src/core/canvas.test.ts

@@ -0,0 +1,92 @@
+import { describe, expect, test } from "bun:test"
+import stringWidth from "string-width"
+import { DiagramCanvas, type DiagramCanvasCell } from "./canvas.js"
+
+describe("DiagramCanvas", () => {
+  test("writes cells and text while clipping out-of-bounds positions", () => {
+    const canvas = new DiagramCanvas<"label">(5, 2)
+
+    canvas.setCell(0, 0, "A", "label")
+    canvas.setCell(9, 0, "X", "label")
+    canvas.setText(2, 1, "hey", "label")
+
+    expect(canvas.toString()).toBe("A\n  hey")
+  })
+
+  test("uses measured character widths for text placement", () => {
+    const canvas = new DiagramCanvas<"label">(5, 1)
+
+    canvas.setText(0, 0, "a界b", "label")
+
+    expect(canvas.toString()).toBe("a界b")
+    expect(stringWidth(canvas.toString())).toBe(4)
+  })
+
+  test("preserves combined graphemes while placing later text", () => {
+    const canvas = new DiagramCanvas<"label">(4, 1)
+
+    canvas.setText(0, 0, "e\u0301x", "label")
+
+    expect(canvas.toString()).toBe("e\u0301x")
+    expect(stringWidth(canvas.toString())).toBe(2)
+  })
+
+  test("merges cells through the adapter-provided merge function", () => {
+    type Style = "line"
+    const canvas = new DiagramCanvas<Style>(3, 1, {
+      mergeCell: (existing, incoming): DiagramCanvasCell<Style> => ({
+        ...incoming,
+        char: existing.char === "─" && incoming.char === "│" ? "┼" : incoming.char,
+      }),
+    })
+
+    canvas.setCell(1, 0, "─", "line")
+    canvas.setCell(1, 0, "│", "line")
+
+    expect(canvas.toString()).toBe(" ┼")
+  })
+
+  test("iterates style and metadata runs", () => {
+    interface Metadata {
+      stateId?: string
+    }
+    const canvas = new DiagramCanvas<"state", Metadata>(4, 1)
+    const runs: string[] = []
+
+    canvas.setText(0, 0, "AB", "state", { stateId: "A" })
+    canvas.setText(2, 0, "CD", "state", { stateId: "B" })
+    canvas.forEachRun(
+      (run) => runs.push(`${run.text}:${run.style}:${run.cell.stateId}`),
+      () => runs.push("newline"),
+      { key: (cell) => [cell.style, cell.stateId] },
+    )
+
+    expect(runs).toEqual(["AB:state:A", "CD:state:B"])
+  })
+
+  test("can trim bottom whitespace for renderers with dynamic height", () => {
+    const canvas = new DiagramCanvas<"label">(3, 3)
+    const runs: string[] = []
+    canvas.setText(0, 0, "top", "label")
+
+    expect(canvas.toString()).toBe("top\n\n")
+    expect(canvas.toString({ trimBottom: true })).toBe("top")
+    expect(canvas.getTextSize()).toEqual({ width: 3, height: 3 })
+    expect(canvas.getTextSize({ trimBottom: true })).toEqual({ width: 3, height: 1 })
+
+    canvas.forEachRun(
+      (run) => runs.push(run.text),
+      () => runs.push("newline"),
+      { trimBottom: true },
+    )
+    expect(runs).toEqual(["top"])
+  })
+
+  test("can trim unused leading whitespace reserved by layout", () => {
+    const canvas = new DiagramCanvas<"label">(3, 3)
+    canvas.setText(0, 2, "end", "label")
+
+    expect(canvas.toString({ trimTop: true })).toBe("end")
+    expect(canvas.getTextSize({ trimTop: true })).toEqual({ width: 3, height: 1 })
+  })
+})

packages/merman/src/core/canvas.ts

@@ -0,0 +1,169 @@
+import stringWidth from "string-width"
+import { diagramTextGraphemes } from "./text.js"
+
+export type DiagramCanvasCell<Style extends string, Metadata extends object = object> = {
+  char: string
+  style?: Style
+} & Partial<Metadata>
+
+export interface DiagramCanvasRun<Style extends string, Metadata extends object = object> {
+  text: string
+  style: Style | undefined
+  cell: DiagramCanvasCell<Style, Metadata>
+}
+
+export interface DiagramCanvasOptions<Style extends string, Metadata extends object = object> {
+  measure?: (text: string) => number
+  mergeCell?: (
+    existing: DiagramCanvasCell<Style, Metadata>,
+    incoming: DiagramCanvasCell<Style, Metadata>,
+  ) => DiagramCanvasCell<Style, Metadata>
+}
+
+export interface DiagramCanvasTextOptions {
+  trimTop?: boolean
+  trimBottom?: boolean
+}
+
+export interface DiagramCanvasTextSize {
+  width: number
+  height: number
+}
+
+export type DiagramCanvasTextMetadata<Metadata extends object> =
+  | Partial<Metadata>
+  | ((x: number, y: number) => Partial<Metadata>)
+
+export interface DiagramCanvasRunOptions<Style extends string, Metadata extends object = object> {
+  key?: (cell: DiagramCanvasCell<Style, Metadata>) => readonly unknown[]
+  trimTop?: boolean
+  trimBottom?: boolean
+}
+
+function createEmptyCell<Style extends string, Metadata extends object>(): DiagramCanvasCell<Style, Metadata> {
+  return { char: " " } as DiagramCanvasCell<Style, Metadata>
+}
+
+function sameKey(left: readonly unknown[] | undefined, right: readonly unknown[]): boolean {
+  return Boolean(left && left.length === right.length && left.every((value, index) => Object.is(value, right[index])))
+}
+
+export class DiagramCanvas<Style extends string, Metadata extends object = object> {
+  readonly rows: Array<Array<DiagramCanvasCell<Style, Metadata>>>
+
+  private readonly measure: (text: string) => number
+  private readonly mergeCell?: DiagramCanvasOptions<Style, Metadata>["mergeCell"]
+
+  constructor(
+    readonly width: number,
+    readonly height: number,
+    options: DiagramCanvasOptions<Style, Metadata> = {},
+  ) {
+    this.measure = options.measure ?? stringWidth
+    this.mergeCell = options.mergeCell
+    this.rows = Array.from({ length: height }, () => Array.from({ length: width }, () => createEmptyCell()))
+  }
+
+  private rowTextEnd(row: Array<DiagramCanvasCell<Style, Metadata>>): number {
+    let rowEnd = row.length
+    while (rowEnd > 0 && row[rowEnd - 1]?.char === " ") rowEnd -= 1
+    return rowEnd
+  }
+
+  private rowText(row: Array<DiagramCanvasCell<Style, Metadata>>, rowEnd = this.rowTextEnd(row)): string {
+    return row
+      .slice(0, rowEnd)
+      .map((cell) => cell.char)
+      .join("")
+  }
+
+  private textRowRange(trimTop: boolean, trimBottom: boolean): { start: number; end: number } {
+    let start = 0
+    let end = this.rows.length
+    if (trimTop) while (start < end && this.rowTextEnd(this.rows[start]!) === 0) start += 1
+    if (trimBottom) while (end > start && this.rowTextEnd(this.rows[end - 1]!) === 0) end -= 1
+    return { start, end }
+  }
+
+  setCell(x: number, y: number, char: string, style?: Style, metadata?: Partial<Metadata>): void {
+    if (y < 0 || y >= this.rows.length || x < 0 || x >= this.rows[y]!.length) return
+
+    const incoming = { char, style, ...metadata } as DiagramCanvasCell<Style, Metadata>
+    this.rows[y]![x] = this.mergeCell?.(this.rows[y]![x]!, incoming) ?? incoming
+  }
+
+  getCell(x: number, y: number): DiagramCanvasCell<Style, Metadata> | undefined {
+    return this.rows[y]?.[x]
+  }
+
+  setText(x: number, y: number, text: string, style?: Style, metadata?: DiagramCanvasTextMetadata<Metadata>): void {
+    let offset = 0
+    for (const grapheme of diagramTextGraphemes(text)) {
+      const width = Math.max(1, this.measure(grapheme))
+      const metadataAt = (cellX: number) => (typeof metadata === "function" ? metadata(cellX, y) : metadata)
+      this.setCell(x + offset, y, grapheme, style, metadataAt(x + offset))
+      for (let continuation = 1; continuation < width; continuation++) {
+        this.setCell(x + offset + continuation, y, "", style, metadataAt(x + offset + continuation))
+      }
+      offset += width
+    }
+  }
+
+  toString(options: DiagramCanvasTextOptions = {}): string {
+    const lines: string[] = []
+    const rows = this.textRowRange(options.trimTop ?? false, options.trimBottom ?? false)
+    for (let rowIndex = rows.start; rowIndex < rows.end; rowIndex++) {
+      lines.push(this.rowText(this.rows[rowIndex]!))
+    }
+    return lines.join("\n")
+  }
+
+  getTextSize(options: DiagramCanvasTextOptions = {}): DiagramCanvasTextSize {
+    const rows = this.textRowRange(options.trimTop ?? false, options.trimBottom ?? false)
+    let width = 0
+    for (let rowIndex = rows.start; rowIndex < rows.end; rowIndex++) {
+      const row = this.rows[rowIndex]!
+      const rowEnd = this.rowTextEnd(row)
+      if (rowEnd > 0) width = Math.max(width, this.measure(this.rowText(row, rowEnd)))
+    }
+    return { width, height: rows.end - rows.start }
+  }
+
+  forEachRun(
+    onRun: (run: DiagramCanvasRun<Style, Metadata>) => void,
+    onLineEnd: () => void,
+    options: DiagramCanvasRunOptions<Style, Metadata> = {},
+  ): void {
+    const key = options.key
+    const rows = this.textRowRange(options.trimTop ?? false, options.trimBottom ?? false)
+
+    for (let rowIndex = rows.start; rowIndex < rows.end; rowIndex++) {
+      const row = this.rows[rowIndex]!
+      const rowEnd = this.rowTextEnd(row)
+
+      let currentCell: DiagramCanvasCell<Style, Metadata> | undefined
+      let currentKey: readonly unknown[] | undefined
+      let currentText = ""
+      const flush = () => {
+        if (!currentText || !currentCell) return
+        onRun({ text: currentText, style: currentCell.style, cell: currentCell })
+        currentText = ""
+      }
+
+      for (let x = 0; x < rowEnd; x++) {
+        const cell = row[x]!
+        const nextKey = key?.(cell)
+        const sameRun = currentCell && (key ? sameKey(currentKey, nextKey!) : currentCell.style === cell.style)
+        if (!sameRun) {
+          flush()
+          currentCell = cell
+          currentKey = nextKey
+        }
+        currentText += cell.char
+      }
+
+      flush()
+      if (rowIndex < rows.end - 1) onLineEnd()
+    }
+  }
+}

packages/merman/src/core/color/map.ts

@@ -0,0 +1,59 @@
+import { parseColor, RGBA, type ColorInput } from "@opentui/core"
+import { colorsEqual } from "./style.js"
+
+export type DiagramColorMapInput = Record<string, ColorInput | undefined> | ReadonlyMap<string, ColorInput | undefined>
+
+export const DIAGRAM_CELL_COLOR_LEVEL_SEPARATOR = "::cell:"
+export const DIAGRAM_CELL_COLOR_LEVEL_COUNT = 6
+
+export function diagramCellColorKey(id: string, level: number): string {
+  const normalizedLevel = Math.max(0, Math.min(DIAGRAM_CELL_COLOR_LEVEL_COUNT - 1, Math.round(level)))
+  return `${id}${DIAGRAM_CELL_COLOR_LEVEL_SEPARATOR}${normalizedLevel}`
+}
+
+export function diagramRadialCellColorLevel(
+  bounds: { width: number; height: number; centerX: number; centerY: number },
+  x: number,
+  y: number,
+  border = false,
+): number {
+  const halfWidth = Math.max(1, (bounds.width - 1) / 2)
+  const halfHeight = Math.max(1, (bounds.height - 1) / 2)
+  const dx = (x - bounds.centerX) / halfWidth
+  const dy = (y - bounds.centerY) / halfHeight
+  const distance = Math.sqrt(dx * dx + dy * dy)
+  const level = Math.round((1 - Math.min(1, distance)) * (DIAGRAM_CELL_COLOR_LEVEL_COUNT - 1))
+  return border ? Math.min(1, level) : level
+}
+
+export function baseDiagramCellColorKey(id: string): string {
+  const index = id.lastIndexOf(DIAGRAM_CELL_COLOR_LEVEL_SEPARATOR)
+  return index === -1 ? id : id.slice(0, index)
+}
+
+export function mappedDiagramColor(
+  colors: ReadonlyMap<string, RGBA> | undefined,
+  id: string | undefined,
+): RGBA | undefined {
+  return id ? (colors?.get(id) ?? colors?.get(baseDiagramCellColorKey(id))) : undefined
+}
+
+export function normalizeDiagramColorMap(value: DiagramColorMapInput | undefined): Map<string, RGBA> {
+  const colors = new Map<string, RGBA>()
+  if (!value) return colors
+
+  const entries = value instanceof Map ? value.entries() : Object.entries(value)
+  for (const [id, color] of entries) {
+    if (color !== undefined) colors.set(id, parseColor(color))
+  }
+
+  return colors
+}
+
+export function diagramColorMapsEqual(left: ReadonlyMap<string, RGBA>, right: ReadonlyMap<string, RGBA>): boolean {
+  if (left.size !== right.size) return false
+  for (const [id, color] of left) {
+    if (!colorsEqual(color, right.get(id))) return false
+  }
+  return true
+}

packages/merman/src/core/color/style.test.ts

@@ -0,0 +1,82 @@
+import { describe, expect, test } from "bun:test"
+import { RGBA } from "@opentui/core"
+import {
+  baseDiagramCellColorKey,
+  diagramCellColorKey,
+  diagramColorMapsEqual,
+  diagramRadialCellColorLevel,
+  mappedDiagramColor,
+  normalizeDiagramColorMap,
+} from "./map.js"
+import {
+  ansiBg,
+  ansiFg,
+  blendColor,
+  brightenColor,
+  createAnsiRampTheme,
+  mixRgb,
+  numberedStyleKeys,
+  rgba,
+} from "./style.js"
+
+describe("diagram style helpers", () => {
+  test("mixes rgb values and emits truecolor ANSI", () => {
+    expect(mixRgb([0, 10, 20], [10, 30, 60], 0.5)).toEqual([5, 20, 40])
+    expect(ansiFg([1, 2, 3])).toBe("\x1b[38;2;1;2;3m")
+    expect(ansiBg([4, 5, 6])).toBe("\x1b[48;2;4;5;6m")
+  })
+
+  test("converts rgb tuples and blends optional RGBA values", () => {
+    const black = RGBA.fromInts(0, 0, 0, 255)
+    const white = RGBA.fromInts(10, 20, 30, 255)
+
+    expect(rgba([1, 2, 3]).equals(RGBA.fromInts(1, 2, 3, 255))).toBe(true)
+    expect(blendColor(black, white, 0.5).equals(RGBA.fromInts(5, 10, 15, 255))).toBe(true)
+    expect(blendColor(undefined, white, 0.5)?.equals(white)).toBe(true)
+    expect(blendColor(undefined, undefined, 0.5)).toBeUndefined()
+  })
+
+  test("brightens colors toward white", () => {
+    const color = brightenColor(RGBA.fromInts(100, 150, 200, 255), 0.5)
+
+    expect(color?.equals(RGBA.fromInts(178, 203, 228, 255))).toBe(true)
+    expect(brightenColor(undefined)).toBeUndefined()
+  })
+
+  test("creates numbered style keys and ANSI ramps", () => {
+    const styles = numberedStyleKeys("requestFade", [1, 2, 3] as const)
+    const theme = createAnsiRampTheme(styles, [0, 0, 0], [12, 24, 36])
+
+    expect(styles).toEqual(["requestFade1", "requestFade2", "requestFade3"])
+    expect(theme.requestFade1).toBe("\x1b[38;2;3;6;9m")
+    expect(theme.requestFade2).toBe("\x1b[38;2;6;12;18m")
+    expect(theme.requestFade3).toBe("\x1b[38;2;9;18;27m")
+  })
+
+  test("normalizes and resolves leveled diagram color maps", () => {
+    const red = RGBA.fromInts(255, 0, 0, 255)
+    const blue = RGBA.fromInts(0, 0, 255, 255)
+    const colors = normalizeDiagramColorMap({
+      A: red,
+      B: undefined,
+      [diagramCellColorKey("C", 2)]: blue,
+    })
+
+    expect(colors.size).toBe(2)
+    expect(diagramCellColorKey("A", -1)).toBe("A::cell:0")
+    expect(diagramCellColorKey("A", 10)).toBe("A::cell:5")
+    expect(baseDiagramCellColorKey("A::cell:3")).toBe("A")
+    expect(mappedDiagramColor(colors, "A")?.equals(red)).toBe(true)
+    expect(mappedDiagramColor(colors, "C::cell:2")?.equals(blue)).toBe(true)
+    expect(mappedDiagramColor(colors, "C::cell:4")).toBeUndefined()
+    expect(diagramColorMapsEqual(colors, normalizeDiagramColorMap(new Map(colors)))).toBe(true)
+  })
+
+  test("computes radial diagram cell color levels", () => {
+    const bounds = { width: 9, height: 5, centerX: 4, centerY: 2 }
+
+    expect(diagramRadialCellColorLevel(bounds, 4, 2)).toBe(5)
+    expect(diagramRadialCellColorLevel(bounds, 0, 0)).toBe(0)
+    expect(diagramRadialCellColorLevel(bounds, 4, 2, true)).toBe(1)
+  })
+})

packages/merman/src/core/color/style.ts

@@ -0,0 +1,93 @@
+import { RGBA } from "@opentui/core"
+
+export type DiagramRgb = readonly [number, number, number]
+export type DiagramFadeStep = 1 | 2 | 3 | 4 | 5
+
+export const DIAGRAM_FADE_STEPS = [1, 2, 3, 4, 5] as const satisfies readonly DiagramFadeStep[]
+
+export function numberedStyleKeys<Prefix extends string, Step extends number>(
+  prefix: Prefix,
+  steps: readonly Step[],
+): Array<`${Prefix}${Step}`> {
+  return steps.map((step) => `${prefix}${step}` as `${Prefix}${Step}`)
+}
+
+export function mixChannel(left: number, right: number, amount: number): number {
+  return Math.round(left + (right - left) * amount)
+}
+
+export function mixRgb(left: DiagramRgb, right: DiagramRgb, amount: number): DiagramRgb {
+  return [
+    mixChannel(left[0], right[0], amount),
+    mixChannel(left[1], right[1], amount),
+    mixChannel(left[2], right[2], amount),
+  ]
+}
+
+export function ansiFg(rgb: DiagramRgb): string {
+  return `\x1b[38;2;${rgb[0]};${rgb[1]};${rgb[2]}m`
+}
+
+export function ansiBg(rgb: DiagramRgb): string {
+  return `\x1b[48;2;${rgb[0]};${rgb[1]};${rgb[2]}m`
+}
+
+export function rgba(rgb: DiagramRgb): RGBA {
+  return RGBA.fromInts(rgb[0], rgb[1], rgb[2], 255)
+}
+
+export function blendColor(from: RGBA, to: RGBA, amount: number): RGBA
+export function blendColor(from: RGBA | undefined, to: RGBA | undefined, amount: number): RGBA | undefined
+export function blendColor(from: RGBA | undefined, to: RGBA | undefined, amount: number): RGBA | undefined {
+  if (!from && !to) return undefined
+  if (!from) return to
+  if (!to) return from
+
+  const [fromR, fromG, fromB, fromA] = from.toInts()
+  const [toR, toG, toB, toA] = to.toInts()
+  const mix = (left: number, right: number) => left + (right - left) * amount
+
+  return RGBA.fromInts(mix(fromR, toR), mix(fromG, toG), mix(fromB, toB), mix(fromA, toA))
+}
+
+export function colorsEqual(left?: RGBA, right?: RGBA): boolean {
+  if (!left || !right) return left === right
+  return left.equals(right)
+}
+
+export function brightenColor(color: RGBA | undefined, amount: number = 0.35): RGBA | undefined {
+  if (!color) return undefined
+
+  const [r, g, b, a] = color.toInts()
+  return RGBA.fromInts(mixChannel(r, 255, amount), mixChannel(g, 255, amount), mixChannel(b, 255, amount), a)
+}
+
+export function createAnsiRampTheme<Style extends string>(
+  styles: readonly Style[],
+  from: DiagramRgb,
+  to: DiagramRgb,
+): Record<Style, string> {
+  return Object.fromEntries(
+    styles.map((style, index) => [style, ansiFg(mixRgb(from, to, (index + 1) / (styles.length + 1)))]),
+  ) as Record<Style, string>
+}
+
+export function createColorRampTheme<Style extends string>(
+  styles: readonly Style[],
+  from: RGBA,
+  to: RGBA,
+): Record<Style, RGBA>
+export function createColorRampTheme<Style extends string>(
+  styles: readonly Style[],
+  from: RGBA | undefined,
+  to: RGBA | undefined,
+): Record<Style, RGBA | undefined>
+export function createColorRampTheme<Style extends string>(
+  styles: readonly Style[],
+  from: RGBA | undefined,
+  to: RGBA | undefined,
+): Record<Style, RGBA | undefined> {
+  return Object.fromEntries(
+    styles.map((style, index) => [style, blendColor(from, to, (index + 1) / (styles.length + 1))]),
+  ) as Record<Style, RGBA | undefined>
+}

packages/merman/src/core/drawing.test.ts

@@ -0,0 +1,116 @@
+import { describe, expect, test } from "bun:test"
+import { BorderChars } from "@opentui/core"
+import { DiagramCanvas } from "./canvas.js"
+import {
+  diagramArrowHead,
+  drawDiagramDiamond,
+  drawDiagramFrame,
+  drawOrthogonalPath,
+  mergeDiagramLineGlyph,
+} from "./drawing.js"
+
+describe("diagram drawing", () => {
+  test("merges line glyphs with square and rounded corners", () => {
+    expect(mergeDiagramLineGlyph("─", "│")).toBe("┼")
+    expect(mergeDiagramLineGlyph("─", "│", "rounded")).toBe("┼")
+    expect(mergeDiagramLineGlyph("─", "╭", "rounded")).toBe("┬")
+    expect(mergeDiagramLineGlyph("a", "│")).toBeUndefined()
+  })
+
+  test("draws frames through caller-provided cell writers", () => {
+    const canvas = new DiagramCanvas<"frame">(8, 4)
+    drawDiagramFrame(
+      { left: 1, top: 0, width: 6, height: 4, centerX: 4, centerY: 2 },
+      BorderChars.rounded,
+      (x, y, char) => canvas.setCell(x, y, char, "frame"),
+    )
+
+    expect(canvas.toString({ trimBottom: true })).toBe(" ╭────╮\n │    │\n │    │\n ╰────╯")
+  })
+
+  test("draws diamond frames through caller-provided cell writers", () => {
+    const canvas = new DiagramCanvas<"frame">(9, 5)
+    drawDiagramDiamond({ left: 0, top: 0, width: 9, height: 5, centerX: 4, centerY: 2 }, (x, y, char) =>
+      canvas.setCell(x, y, char, "frame"),
+    )
+
+    expect(canvas.toString({ trimBottom: true })).toBe("  ╭───╮\n╭─╯   ╰─╮\n│       │\n╰─╮   ╭─╯\n  ╰───╯")
+    expect(canvas.toString()).not.toMatch(/[╱╲\\/]/)
+  })
+
+  test("draws orthogonal paths with selected corner style", () => {
+    const canvas = new DiagramCanvas<"edge">(7, 4)
+    drawOrthogonalPath(
+      [
+        { x: 0, y: 0 },
+        { x: 3, y: 0 },
+        { x: 3, y: 2 },
+        { x: 6, y: 2 },
+      ],
+      (x, y, char) => canvas.setCell(x, y, char, "edge"),
+      { cornerStyle: "rounded" },
+    )
+
+    expect(canvas.toString({ trimBottom: true })).toBe("───╮\n   │\n   ╰──")
+  })
+
+  test("draws orthogonal paths with heavy line style", () => {
+    const canvas = new DiagramCanvas<"edge">(7, 4)
+    drawOrthogonalPath(
+      [
+        { x: 0, y: 0 },
+        { x: 3, y: 0 },
+        { x: 3, y: 2 },
+        { x: 6, y: 2 },
+      ],
+      (x, y, char) => canvas.setCell(x, y, char, "edge"),
+      { lineStyle: "heavy" },
+    )
+
+    expect(canvas.toString({ trimBottom: true })).toBe("━━━┓\n   ┃\n   ┗━━")
+  })
+
+  test("draws orthogonal paths with dashed line style", () => {
+    const canvas = new DiagramCanvas<"edge">(9, 1)
+    drawOrthogonalPath(
+      [
+        { x: 0, y: 0 },
+        { x: 8, y: 0 },
+      ],
+      (x, y, char) => canvas.setCell(x, y, char, "edge"),
+      { lineStyle: "dashed" },
+    )
+
+    expect(canvas.toString({ trimBottom: true })).toBe("─ ─ ─ ─")
+  })
+
+  test("keeps container frame policy separate from edge drawing policy", () => {
+    const canvas = new DiagramCanvas<"group" | "edge">(8, 5, {
+      mergeCell: (existing, incoming) => {
+        if (incoming.style === "edge") return incoming
+        return existing.char === " " ? incoming : existing
+      },
+    })
+
+    drawDiagramFrame(
+      { left: 1, top: 0, width: 6, height: 5, centerX: 4, centerY: 2 },
+      BorderChars.rounded,
+      (x, y, char) => canvas.setCell(x, y, char, "group"),
+    )
+    drawOrthogonalPath(
+      [
+        { x: 0, y: 2 },
+        { x: 7, y: 2 },
+      ],
+      (x, y, char) => canvas.setCell(x, y, char, "edge"),
+    )
+    canvas.setCell(7, 2, "▶", "edge")
+
+    expect(canvas.toString({ trimBottom: true })).toBe(" ╭────╮\n │    │\n───────▶\n │    │\n ╰────╯")
+  })
+
+  test("selects filled and line arrow heads", () => {
+    expect(diagramArrowHead("right")).toBe("▶")
+    expect(diagramArrowHead("left", "line")).toBe("←")
+  })
+})

packages/merman/src/core/drawing.ts

@@ -0,0 +1,295 @@
+import { BorderChars, type BorderCharacters } from "@opentui/core"
+import {
+  directionBetween,
+  walkOrthogonalSegment,
+  type DiagramBounds,
+  type DiagramDirection,
+  type DiagramPoint,
+} from "./geometry.js"
+
+export type DiagramLineCornerStyle = "square" | "rounded"
+export type DiagramLineStyle = "single" | "heavy" | "dashed"
+export type DiagramArrowHeadStyle = "filled" | "line"
+
+export interface DiagramDiamondCharacters {
+  topLeft: string
+  topRight: string
+  upperLeft: string
+  upperLeftJoin: string
+  upperRightJoin: string
+  upperRight: string
+  vertical: string
+  lowerLeft: string
+  lowerLeftJoin: string
+  lowerRightJoin: string
+  lowerRight: string
+  bottomLeft: string
+  bottomRight: string
+  horizontal: string
+}
+
+export const DIAGRAM_ARROW_HEADS = new Set(["▶", "◀", "▼", "▲", "→", "←", "↓", "↑"])
+const HEAVY_LINE_GLYPHS = new Set(Object.values(BorderChars.heavy))
+
+export const DIAGRAM_DIAMOND_CHARS = {
+  topLeft: "╭",
+  topRight: "╮",
+  upperLeft: "╭",
+  upperLeftJoin: "╯",
+  upperRightJoin: "╰",
+  upperRight: "╮",
+  vertical: "│",
+  lowerLeft: "╰",
+  lowerLeftJoin: "╮",
+  lowerRightJoin: "╭",
+  lowerRight: "╯",
+  bottomLeft: "╰",
+  bottomRight: "╯",
+  horizontal: "─",
+} as const satisfies DiagramDiamondCharacters
+
+export function diagramDiamondCharactersFromBorder(chars: BorderCharacters): DiagramDiamondCharacters {
+  return {
+    topLeft: chars.topLeft,
+    topRight: chars.topRight,
+    upperLeft: chars.topLeft,
+    upperLeftJoin: chars.bottomRight,
+    upperRightJoin: chars.bottomLeft,
+    upperRight: chars.topRight,
+    vertical: chars.vertical,
+    lowerLeft: chars.bottomLeft,
+    lowerLeftJoin: chars.topRight,
+    lowerRightJoin: chars.topLeft,
+    lowerRight: chars.bottomRight,
+    bottomLeft: chars.bottomLeft,
+    bottomRight: chars.bottomRight,
+    horizontal: chars.horizontal,
+  }
+}
+
+function lineDirections(char: string): readonly DiagramDirection[] | undefined {
+  switch (char) {
+    case "─":
+      return ["left", "right"]
+    case "│":
+      return ["up", "down"]
+    case "━":
+      return ["left", "right"]
+    case "┃":
+      return ["up", "down"]
+    case "┌":
+    case "╭":
+    case "┏":
+      return ["right", "down"]
+    case "┐":
+    case "╮":
+    case "┓":
+      return ["left", "down"]
+    case "└":
+    case "╰":
+    case "┗":
+      return ["up", "right"]
+    case "┘":
+    case "╯":
+    case "┛":
+      return ["up", "left"]
+    case "├":
+    case "┣":
+      return ["up", "down", "right"]
+    case "┤":
+    case "┫":
+      return ["up", "down", "left"]
+    case "┬":
+    case "┳":
+      return ["left", "right", "down"]
+    case "┴":
+    case "┻":
+      return ["left", "right", "up"]
+    case "┼":
+    case "╋":
+      return ["up", "down", "left", "right"]
+    default:
+      return undefined
+  }
+}
+
+export function diagramLineGlyph(
+  directions: ReadonlySet<DiagramDirection>,
+  cornerStyle: DiagramLineCornerStyle = "square",
+  lineStyle: DiagramLineStyle = "single",
+): string {
+  const up = directions.has("up")
+  const down = directions.has("down")
+  const left = directions.has("left")
+  const right = directions.has("right")
+  if (lineStyle === "heavy") {
+    const chars = BorderChars.heavy
+    if (up && down && left && right) return chars.cross
+    if (up && down && right) return chars.leftT
+    if (up && down && left) return chars.rightT
+    if (left && right && down) return chars.topT
+    if (left && right && up) return chars.bottomT
+    if (up && right) return chars.bottomLeft
+    if (up && left) return chars.bottomRight
+    if (down && right) return chars.topLeft
+    if (down && left) return chars.topRight
+    if (up || down) return chars.vertical
+    return chars.horizontal
+  }
+  if (up && down && left && right) return "┼"
+  if (up && down && right) return "├"
+  if (up && down && left) return "┤"
+  if (left && right && down) return "┬"
+  if (left && right && up) return "┴"
+  if (up && right) return cornerStyle === "rounded" ? "╰" : "└"
+  if (up && left) return cornerStyle === "rounded" ? "╯" : "┘"
+  if (down && right) return cornerStyle === "rounded" ? "╭" : "┌"
+  if (down && left) return cornerStyle === "rounded" ? "╮" : "┐"
+  if (up || down) return "│"
+  return "─"
+}
+
+function isHeavyLineGlyph(char: string): boolean {
+  return HEAVY_LINE_GLYPHS.has(char)
+}
+
+function segmentGlyph(direction: DiagramDirection, lineStyle: DiagramLineStyle | undefined): string {
+  const directions = new Set<DiagramDirection>(
+    direction === "left" || direction === "right" ? ["left", "right"] : ["up", "down"],
+  )
+  return diagramLineGlyph(directions, "square", lineStyle === "heavy" ? "heavy" : "single")
+}
+
+export function mergeDiagramLineGlyph(
+  existing: string,
+  incoming: string,
+  cornerStyle: DiagramLineCornerStyle = "square",
+): string | undefined {
+  const existingDirections = lineDirections(existing)
+  const incomingDirections = lineDirections(incoming)
+  if (!existingDirections || !incomingDirections) return undefined
+
+  return diagramLineGlyph(
+    new Set([...existingDirections, ...incomingDirections]),
+    cornerStyle,
+    isHeavyLineGlyph(existing) && isHeavyLineGlyph(incoming) ? "heavy" : "single",
+  )
+}
+
+export function diagramArrowHead(direction: DiagramDirection, style: DiagramArrowHeadStyle = "filled"): string {
+  if (style === "line") {
+    if (direction === "right") return "→"
+    if (direction === "left") return "←"
+    if (direction === "up") return "↑"
+    return "↓"
+  }
+
+  if (direction === "right") return "▶"
+  if (direction === "left") return "◀"
+  if (direction === "up") return "▲"
+  return "▼"
+}
+
+export function diagramArrowHeadBetween(
+  from: DiagramPoint,
+  to: DiagramPoint,
+  style: DiagramArrowHeadStyle = "filled",
+): string {
+  const direction = directionBetween(from, to)
+  return direction ? diagramArrowHead(direction, style) : diagramArrowHead("right", style)
+}
+
+export function drawDiagramFrame(
+  bounds: DiagramBounds,
+  chars: BorderCharacters,
+  setCell: (x: number, y: number, char: string) => void,
+): void {
+  setCell(bounds.left, bounds.top, chars.topLeft)
+  setCell(bounds.left + bounds.width - 1, bounds.top, chars.topRight)
+  setCell(bounds.left, bounds.top + bounds.height - 1, chars.bottomLeft)
+  setCell(bounds.left + bounds.width - 1, bounds.top + bounds.height - 1, chars.bottomRight)
+  for (let x = bounds.left + 1; x < bounds.left + bounds.width - 1; x++) {
+    setCell(x, bounds.top, chars.horizontal)
+    setCell(x, bounds.top + bounds.height - 1, chars.horizontal)
+  }
+  for (let y = bounds.top + 1; y < bounds.top + bounds.height - 1; y++) {
+    setCell(bounds.left, y, chars.vertical)
+    setCell(bounds.left + bounds.width - 1, y, chars.vertical)
+  }
+}
+
+export function drawDiagramDiamond(
+  bounds: DiagramBounds,
+  setCell: (x: number, y: number, char: string) => void,
+  chars: DiagramDiamondCharacters = DIAGRAM_DIAMOND_CHARS,
+): void {
+  const left = bounds.left
+  const right = bounds.left + bounds.width - 1
+  const top = bounds.top
+  const bottom = bounds.top + bounds.height - 1
+  const capInset = Math.min(2, Math.max(1, Math.floor((bounds.width - 1) / 2)))
+  const capLeft = left + capInset
+  const capRight = right - capInset
+
+  setCell(capLeft, top, chars.topLeft)
+  for (let x = capLeft + 1; x < capRight; x++) setCell(x, top, chars.horizontal)
+  setCell(capRight, top, chars.topRight)
+
+  setCell(left, top + 1, chars.upperLeft)
+  for (let x = left + 1; x < capLeft; x++) setCell(x, top + 1, chars.horizontal)
+  setCell(capLeft, top + 1, chars.upperLeftJoin)
+  setCell(capRight, top + 1, chars.upperRightJoin)
+  for (let x = capRight + 1; x < right; x++) setCell(x, top + 1, chars.horizontal)
+  setCell(right, top + 1, chars.upperRight)
+
+  for (let y = top + 2; y < bottom - 1; y++) {
+    setCell(left, y, chars.vertical)
+    setCell(right, y, chars.vertical)
+  }
+
+  setCell(left, bottom - 1, chars.lowerLeft)
+  for (let x = left + 1; x < capLeft; x++) setCell(x, bottom - 1, chars.horizontal)
+  setCell(capLeft, bottom - 1, chars.lowerLeftJoin)
+  setCell(capRight, bottom - 1, chars.lowerRightJoin)
+  for (let x = capRight + 1; x < right; x++) setCell(x, bottom - 1, chars.horizontal)
+  setCell(right, bottom - 1, chars.lowerRight)
+
+  setCell(capLeft, bottom, chars.bottomLeft)
+  for (let x = capLeft + 1; x < capRight; x++) setCell(x, bottom, chars.horizontal)
+  setCell(capRight, bottom, chars.bottomRight)
+}
+
+export function drawOrthogonalPath(
+  points: readonly DiagramPoint[],
+  setCell: (x: number, y: number, char: string) => void,
+  options: { cornerStyle?: DiagramLineCornerStyle; lineStyle?: DiagramLineStyle } = {},
+): void {
+  for (let index = 1; index < points.length; index++) {
+    const from = points[index - 1]!
+    const to = points[index]!
+    const direction = directionBetween(from, to)
+    if (!direction) continue
+    const glyph = segmentGlyph(direction, options.lineStyle)
+    let step = index === 1 ? 0 : 1
+    walkOrthogonalSegment(from, to, index === 1, (point) => {
+      if (options.lineStyle !== "dashed" || step % 2 === 0) setCell(point.x, point.y, glyph)
+      step += 1
+    })
+  }
+
+  for (let index = 1; index < points.length - 1; index++) {
+    const previous = points[index - 1]!
+    const current = points[index]!
+    const next = points[index + 1]!
+    const fromDirection = directionBetween(current, previous)
+    const toDirection = directionBetween(current, next)
+    const directions = new Set<DiagramDirection>()
+    if (fromDirection) directions.add(fromDirection)
+    if (toDirection) directions.add(toDirection)
+    setCell(
+      current.x,
+      current.y,
+      diagramLineGlyph(directions, options.cornerStyle, options.lineStyle === "heavy" ? "heavy" : "single"),
+    )
+  }
+}

packages/merman/src/core/geometry.test.ts

@@ -0,0 +1,112 @@
+import { describe, expect, test } from "bun:test"
+import {
+  diagramBoundsFromBounds,
+  diagramBoundsFromPoints,
+  diagramBoundsFromRect,
+  boundsSidePoint,
+  directionBetween,
+  lane,
+  orthogonalPath,
+  orthogonalPathPoints,
+  pathThrough,
+  pathViaLane,
+  point,
+  translateDiagramBounds,
+  walkOrthogonalSegment,
+} from "./geometry.js"
+
+describe("diagram geometry", () => {
+  test("directions are only defined for orthogonal point pairs", () => {
+    expect(directionBetween(point(1, 2), point(5, 2))).toBe("right")
+    expect(directionBetween(point(1, 2), point(1, 0))).toBe("up")
+    expect(directionBetween(point(1, 2), point(5, 4))).toBeUndefined()
+    expect(directionBetween(point(1, 2), point(1, 2))).toBeUndefined()
+  })
+
+  test("bounds side points describe border and outside ports", () => {
+    const bounds = { left: 10, top: 4, width: 8, height: 5, centerX: 14, centerY: 6 }
+
+    expect(boundsSidePoint(bounds, "left", "border")).toEqual(point(10, 6))
+    expect(boundsSidePoint(bounds, "left")).toEqual(point(9, 6))
+    expect(boundsSidePoint(bounds, "right", "border")).toEqual(point(17, 6))
+    expect(boundsSidePoint(bounds, "right")).toEqual(point(18, 6))
+    expect(boundsSidePoint(bounds, "top", "border")).toEqual(point(14, 4))
+    expect(boundsSidePoint(bounds, "bottom")).toEqual(point(14, 9))
+  })
+
+  test("bounds helpers create, translate, and union bounds", () => {
+    const bounds = diagramBoundsFromRect(2, 3, 5, 4)
+
+    expect(bounds).toEqual({ left: 2, top: 3, width: 5, height: 4, centerX: 4, centerY: 5 })
+    translateDiagramBounds(bounds, 3, -1)
+    expect(bounds).toEqual({ left: 5, top: 2, width: 5, height: 4, centerX: 7, centerY: 4 })
+    expect(diagramBoundsFromBounds([bounds, diagramBoundsFromRect(0, 0, 2, 2)])).toEqual({
+      left: 0,
+      top: 0,
+      width: 10,
+      height: 6,
+      centerX: 5,
+      centerY: 3,
+    })
+    expect(diagramBoundsFromPoints([point(2, 2), point(4, 5)])).toEqual({
+      left: 2,
+      top: 2,
+      width: 3,
+      height: 4,
+      centerX: 3,
+      centerY: 4,
+    })
+  })
+
+  test("paths compose through lanes while removing duplicate joints", () => {
+    expect(pathThrough([point(0, 0), point(0, 0), point(3, 0)])).toEqual([point(0, 0), point(3, 0)])
+    expect(pathViaLane(point(0, 0), lane("x", 4), point(8, 3))).toEqual([
+      point(0, 0),
+      point(4, 0),
+      point(4, 3),
+      point(8, 3),
+    ])
+  })
+
+  test("composed paths do not alias caller-owned points", () => {
+    const start = point(0, 0)
+    const end = point(8, 3)
+    const firstPath = pathViaLane(start, lane("x", 4), end)
+    const secondPath = pathViaLane(start, lane("x", 5), end)
+
+    expect(firstPath[0]).not.toBe(start)
+    expect(firstPath[firstPath.length - 1]).not.toBe(end)
+    expect(firstPath[0]).not.toBe(secondPath[0])
+
+    firstPath[0]!.x += 10
+    firstPath[firstPath.length - 1]!.y += 10
+
+    expect(start).toEqual(point(0, 0))
+    expect(end).toEqual(point(8, 3))
+    expect(secondPath[0]).toEqual(point(0, 0))
+    expect(secondPath[secondPath.length - 1]).toEqual(point(8, 3))
+  })
+
+  test("orthogonal paths choose a terminal lane on the dominant axis", () => {
+    expect(orthogonalPath(point(0, 0), point(10, 4))).toEqual([point(0, 0), point(6, 0), point(6, 4), point(10, 4)])
+  })
+
+  test("orthogonal segment walkers exclude endpoints", () => {
+    const visited: Array<{ x: number; y: number }> = []
+    walkOrthogonalSegment(point(0, 0), point(3, 0), false, (next) => {
+      visited.push(next)
+    })
+    expect(visited).toEqual([point(1, 0), point(2, 0)])
+  })
+
+  test("orthogonal path points include endpoints without duplicating joints", () => {
+    expect(orthogonalPathPoints([point(0, 0), point(3, 0), point(3, 2)])).toEqual([
+      point(0, 0),
+      point(1, 0),
+      point(2, 0),
+      point(3, 0),
+      point(3, 1),
+      point(3, 2),
+    ])
+  })
+})

packages/merman/src/core/geometry.ts

@@ -0,0 +1,347 @@
+export type DiagramAxis = "x" | "y"
+export type DiagramDirection = "up" | "down" | "left" | "right"
+export type DiagramSide = "left" | "right" | "top" | "bottom"
+
+export interface DiagramPoint {
+  x: number
+  y: number
+}
+
+export interface DiagramBounds {
+  left: number
+  top: number
+  width: number
+  height: number
+  centerX: number
+  centerY: number
+}
+
+export interface DiagramSegment {
+  from: DiagramPoint
+  to: DiagramPoint
+  axis: DiagramAxis
+  direction: DiagramDirection
+  length: number
+}
+
+export interface DiagramLane {
+  axis: DiagramAxis
+  coordinate: number
+}
+
+export interface DiagramSpan {
+  start: number
+  end: number
+}
+
+const DIRECTION_AXIS = {
+  left: "x",
+  right: "x",
+  up: "y",
+  down: "y",
+} as const satisfies Record<DiagramDirection, DiagramAxis>
+
+const DIRECTION_SIGN = {
+  left: -1,
+  right: 1,
+  up: -1,
+  down: 1,
+} as const satisfies Record<DiagramDirection, -1 | 1>
+
+const DIRECTION_SIDE = {
+  left: "left",
+  right: "right",
+  up: "top",
+  down: "bottom",
+} as const satisfies Record<DiagramDirection, DiagramSide>
+
+const OPPOSITE_SIDE = {
+  left: "right",
+  right: "left",
+  top: "bottom",
+  bottom: "top",
+} as const satisfies Record<DiagramSide, DiagramSide>
+
+export function point(x: number, y: number): DiagramPoint {
+  return { x, y }
+}
+
+export function diagramBoundsFromRect(left: number, top: number, width: number, height: number): DiagramBounds {
+  return {
+    left,
+    top,
+    width,
+    height,
+    centerX: left + Math.floor(width / 2),
+    centerY: top + Math.floor(height / 2),
+  }
+}
+
+export function translateDiagramBounds(bounds: DiagramBounds, dx: number, dy: number): void {
+  bounds.left += dx
+  bounds.top += dy
+  bounds.centerX += dx
+  bounds.centerY += dy
+}
+
+export function diagramBoundsFromBounds(bounds: readonly DiagramBounds[]): DiagramBounds | undefined {
+  if (bounds.length === 0) return undefined
+  const left = Math.min(...bounds.map((bound) => bound.left))
+  const top = Math.min(...bounds.map((bound) => bound.top))
+  const right = Math.max(...bounds.map((bound) => bound.left + bound.width))
+  const bottom = Math.max(...bounds.map((bound) => bound.top + bound.height))
+  return diagramBoundsFromRect(left, top, right - left, bottom - top)
+}
+
+export function diagramBoundsFromPoints(points: readonly DiagramPoint[]): DiagramBounds | undefined {
+  if (points.length === 0) return undefined
+  const left = Math.min(...points.map((point) => point.x))
+  const top = Math.min(...points.map((point) => point.y))
+  const right = Math.max(...points.map((point) => point.x))
+  const bottom = Math.max(...points.map((point) => point.y))
+  return diagramBoundsFromRect(left, top, right - left + 1, bottom - top + 1)
+}
+
+export function coordinate(point: DiagramPoint, axis: DiagramAxis): number {
+  return point[axis]
+}
+
+export function withCoordinate(point: DiagramPoint, axis: DiagramAxis, value: number): DiagramPoint {
+  return axis === "x" ? { x: value, y: point.y } : { x: point.x, y: value }
+}
+
+export function shiftPoint(point: DiagramPoint, direction: DiagramDirection, distance = 1): DiagramPoint {
+  switch (direction) {
+    case "left":
+      return { x: point.x - distance, y: point.y }
+    case "right":
+      return { x: point.x + distance, y: point.y }
+    case "up":
+      return { x: point.x, y: point.y - distance }
+    case "down":
+      return { x: point.x, y: point.y + distance }
+  }
+}
+
+export function clampPoint(point: DiagramPoint, min: DiagramPoint = { x: 0, y: 0 }): DiagramPoint {
+  return { x: Math.max(min.x, point.x), y: Math.max(min.y, point.y) }
+}
+
+export function samePoint(left: DiagramPoint, right: DiagramPoint): boolean {
+  return left.x === right.x && left.y === right.y
+}
+
+export function directionAxis(direction: DiagramDirection): DiagramAxis {
+  return DIRECTION_AXIS[direction]
+}
+
+export function directionSign(direction: DiagramDirection): -1 | 1 {
+  return DIRECTION_SIGN[direction]
+}
+
+export function sideForDirection(direction: DiagramDirection): DiagramSide {
+  return DIRECTION_SIDE[direction]
+}
+
+export function oppositeSide(side: DiagramSide): DiagramSide {
+  return OPPOSITE_SIDE[side]
+}
+
+export function directionBetween(from: DiagramPoint, to: DiagramPoint): DiagramDirection | undefined {
+  if (from.y === to.y) {
+    if (to.x > from.x) return "right"
+    if (to.x < from.x) return "left"
+  }
+  if (from.x === to.x) {
+    if (to.y > from.y) return "down"
+    if (to.y < from.y) return "up"
+  }
+  return undefined
+}
+
+export function boundsCenter(bounds: DiagramBounds): DiagramPoint {
+  return point(bounds.centerX, bounds.centerY)
+}
+
+export function boundsSidePoint(
+  bounds: DiagramBounds,
+  side: DiagramSide,
+  surface: "border" | "outside" = "outside",
+): DiagramPoint {
+  switch (side) {
+    case "left":
+      return point(bounds.left - (surface === "outside" ? 1 : 0), bounds.centerY)
+    case "right":
+      return point(bounds.left + bounds.width - (surface === "outside" ? 0 : 1), bounds.centerY)
+    case "top":
+      return point(bounds.centerX, bounds.top - (surface === "outside" ? 1 : 0))
+    case "bottom":
+      return point(bounds.centerX, bounds.top + bounds.height - (surface === "outside" ? 0 : 1))
+  }
+}
+
+export function centerCoordinate(bounds: DiagramBounds, axis: DiagramAxis): number {
+  return axis === "x" ? bounds.centerX : bounds.centerY
+}
+
+export function snapCoordinate(source: number, target: number, tolerance: number): number {
+  return Math.abs(source - target) <= tolerance ? target : source
+}
+
+export function pathThrough(points: readonly DiagramPoint[]): DiagramPoint[] {
+  const path: DiagramPoint[] = []
+  for (const next of points) {
+    if (!path.length || !samePoint(path[path.length - 1]!, next)) path.push(point(next.x, next.y))
+  }
+  return path
+}
+
+export function lane(axis: DiagramAxis, coordinate: number): DiagramLane {
+  return { axis, coordinate }
+}
+
+export function pathViaLane(start: DiagramPoint, routeLane: DiagramLane, end: DiagramPoint): DiagramPoint[] {
+  return pathThrough([
+    start,
+    withCoordinate(start, routeLane.axis, routeLane.coordinate),
+    withCoordinate(end, routeLane.axis, routeLane.coordinate),
+    end,
+  ])
+}
+
+function dominantAxis(start: DiagramPoint, end: DiagramPoint): DiagramAxis {
+  return Math.abs(end.x - start.x) >= Math.abs(end.y - start.y) ? "x" : "y"
+}
+
+function terminalLane(start: DiagramPoint, end: DiagramPoint, axis: DiagramAxis, terminalClearance: number): number {
+  const startCoordinate = coordinate(start, axis)
+  const endCoordinate = coordinate(end, axis)
+  const delta = endCoordinate - startCoordinate
+  const sign = Math.sign(delta)
+  if (sign === 0) return endCoordinate
+  return endCoordinate - sign * Math.min(terminalClearance, Math.max(1, Math.abs(delta) - 1))
+}
+
+export function orthogonalPath(
+  start: DiagramPoint,
+  end: DiagramPoint,
+  options: { preferredAxis?: DiagramAxis; terminalClearance?: number } = {},
+): DiagramPoint[] {
+  if (start.x === end.x || start.y === end.y) return pathThrough([start, end])
+
+  const laneAxis = options.preferredAxis ?? dominantAxis(start, end)
+  return pathViaLane(start, lane(laneAxis, terminalLane(start, end, laneAxis, options.terminalClearance ?? 4)), end)
+}
+
+export function segmentBetween(from: DiagramPoint, to: DiagramPoint): DiagramSegment | undefined {
+  const direction = directionBetween(from, to)
+  if (!direction) return undefined
+  return {
+    from,
+    to,
+    axis: directionAxis(direction),
+    direction,
+    length: Math.abs(coordinate(to, directionAxis(direction)) - coordinate(from, directionAxis(direction))),
+  }
+}
+
+export function walkOrthogonalSegment(
+  from: DiagramPoint,
+  to: DiagramPoint,
+  includeStart: boolean,
+  visit: (point: DiagramPoint) => boolean | void,
+): void {
+  const direction = directionBetween(from, to)
+  if (!direction) return
+
+  const dx = direction === "right" ? 1 : direction === "left" ? -1 : 0
+  const dy = direction === "down" ? 1 : direction === "up" ? -1 : 0
+  let cursor = includeStart ? from : point(from.x + dx, from.y + dy)
+
+  while (!samePoint(cursor, to)) {
+    if (visit(cursor) === false) return
+    cursor = point(cursor.x + dx, cursor.y + dy)
+  }
+}
+
+export function orthogonalPathPoints(points: readonly DiagramPoint[]): DiagramPoint[] {
+  const path: DiagramPoint[] = []
+  for (let index = 1; index < points.length; index++) {
+    const from = points[index - 1]!
+    const to = points[index]!
+    const direction = directionBetween(from, to)
+    if (!direction) continue
+
+    const dx = direction === "right" ? 1 : direction === "left" ? -1 : 0
+    const dy = direction === "down" ? 1 : direction === "up" ? -1 : 0
+    let cursor = path.length === 0 ? point(from.x, from.y) : point(from.x + dx, from.y + dy)
+    while (true) {
+      path.push(cursor)
+      if (samePoint(cursor, to)) break
+      cursor = point(cursor.x + dx, cursor.y + dy)
+    }
+  }
+  return path
+}
+
+export function orderedSpan(left: number, right: number): DiagramSpan {
+  return left <= right ? { start: left, end: right } : { start: right, end: left }
+}
+
+export function segmentSpan(segment: DiagramSegment): DiagramSpan {
+  return orderedSpan(coordinate(segment.from, segment.axis), coordinate(segment.to, segment.axis))
+}
+
+export function pointOnSegment(segment: DiagramSegment, coordinateValue: number): DiagramPoint {
+  return withCoordinate(segment.from, segment.axis, coordinateValue)
+}
+
+export function insetSpan(span: DiagramSpan, amount: number): DiagramSpan {
+  return { start: span.start + amount, end: span.end - amount }
+}
+
+export function spanCapacity(span: DiagramSpan): number {
+  return Math.max(0, span.end - span.start + 1)
+}
+
+export function centeredSpanStart(span: DiagramSpan, width: number): number {
+  return span.start + Math.floor((spanCapacity(span) - width) / 2)
+}
+
+export function midpoint(span: DiagramSpan): number {
+  return Math.round((span.start + span.end) / 2)
+}
+
+export function advanceCoordinate(origin: number, direction: DiagramDirection, distance: number): number {
+  return origin + directionSign(direction) * distance
+}
+
+export function beforeNearestCoordinate(
+  points: readonly DiagramPoint[],
+  axis: DiagramAxis,
+  direction: DiagramDirection,
+  clearance: number,
+): number {
+  const coordinates = points.map((point) => coordinate(point, axis))
+  const nearest = directionSign(direction) > 0 ? Math.min(...coordinates) : Math.max(...coordinates)
+  return advanceCoordinate(nearest, direction, -clearance)
+}
+
+export function afterFarthestCoordinate(
+  points: readonly DiagramPoint[],
+  axis: DiagramAxis,
+  direction: DiagramDirection,
+  clearance: number,
+): number {
+  const coordinates = points.map((point) => coordinate(point, axis))
+  const farthest = directionSign(direction) > 0 ? Math.max(...coordinates) : Math.min(...coordinates)
+  return advanceCoordinate(farthest, direction, clearance)
+}
+
+export function keepBefore(preferred: number, boundary: number, direction: DiagramDirection): number {
+  return directionSign(direction) > 0 ? Math.min(preferred, boundary) : Math.max(preferred, boundary)
+}
+
+export function keepAfter(preferred: number, boundary: number, direction: DiagramDirection): number {
+  return directionSign(direction) > 0 ? Math.max(preferred, boundary) : Math.min(preferred, boundary)
+}

packages/merman/src/core/mermaid.ts

@@ -0,0 +1,33 @@
+export interface NumberedMermaidLine {
+  readonly lineNumber: number
+  readonly text: string
+}
+
+export function* numberedMermaidLines(content: string): Generator<NumberedMermaidLine> {
+  const lines = content.split(/\r?\n/)
+  for (let index = 0; index < lines.length; index += 1) {
+    yield { lineNumber: index + 1, text: lines[index]!.trim() }
+  }
+}
+
+export function* meaningfulNumberedMermaidLines(content: string): Generator<NumberedMermaidLine> {
+  for (const line of numberedMermaidLines(content)) {
+    if (line.text && !line.text.startsWith("%%")) yield line
+  }
+}
+
+export function firstMeaningfulMermaidLine(content: string): string | undefined {
+  for (const rawLine of content.split(/\r?\n/)) {
+    const line = rawLine.trim()
+    if (line && !line.startsWith("%%")) return line
+  }
+  return undefined
+}
+
+export function stripMermaidQuotes(value: string): string {
+  const trimmed = value.trim()
+  if ((trimmed.startsWith('"') && trimmed.endsWith('"')) || (trimmed.startsWith("'") && trimmed.endsWith("'"))) {
+    return trimmed.slice(1, -1)
+  }
+  return trimmed
+}

packages/merman/src/core/render-grid.ts

@@ -0,0 +1,54 @@
+import { StyledText, type TextChunk } from "@opentui/core"
+import type { DiagramCanvas, DiagramCanvasRun, DiagramCanvasRunOptions } from "./canvas.js"
+import { ANSI } from "./terminal/ansi.js"
+
+export interface RenderDiagramGridAnsiOptions<
+  Style extends string,
+  Metadata extends object = object,
+> extends DiagramCanvasRunOptions<Style, Metadata> {
+  trimOutputEnd?: boolean
+}
+
+export function renderDiagramGridAnsi<Style extends string, Metadata extends object = object>(
+  grid: DiagramCanvas<Style, Metadata>,
+  styleAnsi: (run: DiagramCanvasRun<Style, Metadata>) => string | undefined,
+  options: RenderDiagramGridAnsiOptions<Style, Metadata> = {},
+): string {
+  const { trimOutputEnd, ...runOptions } = options
+  const output: string[] = []
+
+  grid.forEachRun(
+    (run) => {
+      const ansi = styleAnsi(run)
+      output.push(ansi ? `${ansi}${run.text}${ANSI.reset}` : run.text)
+    },
+    () => {
+      output.push("\n")
+    },
+    runOptions,
+  )
+
+  const text = output.join("")
+  return trimOutputEnd ? text.trimEnd() : text
+}
+
+export function renderDiagramGridStyledText<Style extends string, Metadata extends object = object>(
+  grid: DiagramCanvas<Style, Metadata>,
+  fg: (run: DiagramCanvasRun<Style, Metadata>) => TextChunk["fg"],
+  bg?: (run: DiagramCanvasRun<Style, Metadata>) => TextChunk["bg"],
+  options?: DiagramCanvasRunOptions<Style, Metadata>,
+): StyledText {
+  const chunks: TextChunk[] = []
+
+  grid.forEachRun(
+    (run) => {
+      chunks.push({ __isChunk: true, text: run.text, fg: fg(run), bg: bg?.(run) })
+    },
+    () => {
+      chunks.push({ __isChunk: true, text: "\n" })
+    },
+    options,
+  )
+
+  return new StyledText(chunks)
+}

packages/merman/src/core/terminal/ansi.ts

@@ -0,0 +1,3 @@
+export const ANSI = {
+  reset: "\x1b[0m",
+}

packages/merman/src/core/text-lines.ts

@@ -0,0 +1,3 @@
+export function splitDiagramLines(value: string): string[] {
+  return value.split(/<br\s*\/?>/i).map((line) => line.trim())
+}

packages/merman/src/core/text.test.ts

@@ -0,0 +1,20 @@
+import { describe, expect, test } from "bun:test"
+import { diagramTextWidth, measureDiagramTextBox, splitDiagramLines } from "./text.js"
+
+describe("diagram text helpers", () => {
+  test("splits Mermaid-style line breaks", () => {
+    expect(splitDiagramLines("one<br/> two <br>three")).toEqual(["one", "two", "three"])
+  })
+
+  test("measures padded text boxes", () => {
+    expect(measureDiagramTextBox("wide<br/>x", { paddingX: 2, paddingY: 1 })).toEqual({
+      width: 8,
+      height: 4,
+      lines: ["wide", "x"],
+    })
+  })
+
+  test("measures terminal cell width", () => {
+    expect(diagramTextWidth("abc")).toBe(3)
+  })
+})

packages/merman/src/core/text.ts

@@ -0,0 +1,33 @@
+import stringWidth from "string-width"
+import { splitDiagramLines } from "./text-lines.js"
+
+export { splitDiagramLines } from "./text-lines.js"
+
+export interface DiagramTextBoxSize {
+  width: number
+  height: number
+  lines: string[]
+}
+
+export function diagramTextWidth(value: string): number {
+  return stringWidth(value)
+}
+
+const graphemeSegmenter = new Intl.Segmenter(undefined, { granularity: "grapheme" })
+
+export function* diagramTextGraphemes(value: string): Generator<string> {
+  for (const { segment } of graphemeSegmenter.segment(value)) yield segment
+}
+
+export function measureDiagramTextBox(
+  value: string,
+  options: { paddingX?: number; paddingY?: number; minInnerWidth?: number } = {},
+): DiagramTextBoxSize {
+  const lines = splitDiagramLines(value)
+  const innerWidth = Math.max(...lines.map(diagramTextWidth), options.minInnerWidth ?? 1)
+  return {
+    width: innerWidth + (options.paddingX ?? 0) * 2,
+    height: lines.length + (options.paddingY ?? 0) * 2,
+    lines,
+  }
+}

packages/merman/src/detect.ts

@@ -0,0 +1,11 @@
+import type { MermaidDiagramKind } from "./diagnostics.js"
+import { isMermaidFlowchartDiagram } from "./flowchart/parser.js"
+import { isMermaidSequenceDiagram } from "./sequence/parser.js"
+import { isMermaidStateDiagram } from "./state/parser.js"
+
+export function detectMermaidDiagram(content: string): MermaidDiagramKind | undefined {
+  if (isMermaidFlowchartDiagram(content)) return "flowchart"
+  if (isMermaidSequenceDiagram(content)) return "sequence"
+  if (isMermaidStateDiagram(content)) return "state"
+  return undefined
+}

packages/merman/src/diagnostics.ts

@@ -0,0 +1,16 @@
+export type MermaidDiagramKind = "flowchart" | "sequence" | "state"
+
+/** An otherwise valid diagram contains syntax that merman does not support. */
+export class MermaidSyntaxError extends Error {
+  readonly _tag = "MermaidSyntaxError"
+
+  constructor(
+    readonly kind: MermaidDiagramKind,
+    readonly lineNumber: number,
+    readonly sourceLine: string,
+    reason = "Unsupported syntax",
+  ) {
+    super(`${reason} in ${kind} diagram at line ${lineNumber}: "${sourceLine}"`)
+    this.name = "MermaidSyntaxError"
+  }
+}

packages/merman/src/flowchart/drawing.ts

@@ -0,0 +1,401 @@
+import { BorderChars, type BorderCharacters, type BorderStyle } from "@opentui/core"
+import { orthogonalPathPoints, walkOrthogonalSegment } from "../core/geometry.js"
+import { DiagramCanvas, type DiagramCanvasCell } from "../core/canvas.js"
+import { diagramRadialCellColorLevel } from "../core/color/map.js"
+import { splitDiagramLines } from "../core/text.js"
+import {
+  DIAGRAM_ARROW_HEADS,
+  diagramArrowHeadBetween,
+  diagramDiamondCharactersFromBorder,
+  diagramLineGlyph,
+  drawDiagramDiamond,
+  drawDiagramFrame,
+  drawOrthogonalPath,
+  mergeDiagramLineGlyph,
+} from "../core/drawing.js"
+import { layoutFlowchartDiagram, visualLength } from "./layout.js"
+import { flowchartEdgeLabelLayout } from "./labels.js"
+import type { FlowchartDiagramRenderOptions } from "./options.js"
+import { flowchartDirectionBetween, flowchartSourceConnector } from "./routing.js"
+import {
+  DATABASE_EDGE_FADE_STYLES,
+  flowchartNodeColorKey,
+  NODE_EDGE_FADE_STYLES,
+  type FlowchartCellMetadata,
+  type FlowchartCellStyle,
+  type FlowchartEdgeFadeStyle,
+  type FlowchartGrid,
+} from "./style.js"
+import type {
+  FlowchartDiagram,
+  FlowchartActiveEdgeSelection,
+  FlowchartEdgeRoute,
+  FlowchartNode,
+  FlowchartNodeBounds,
+  FlowchartPoint,
+  FlowchartSubgraphBounds,
+} from "./types.js"
+
+export const DEFAULT_BORDER_STYLE = "rounded" satisfies BorderStyle
+function mergeFlowchartCell(
+  existing: DiagramCanvasCell<FlowchartCellStyle, FlowchartCellMetadata>,
+  incoming: DiagramCanvasCell<FlowchartCellStyle, FlowchartCellMetadata>,
+): DiagramCanvasCell<FlowchartCellStyle, FlowchartCellMetadata> {
+  if (incoming.style !== "edge" && incoming.style !== "activeEdge") return incoming
+  if (existing.style === "label") return incoming.style === "activeEdge" ? incoming : existing
+  if (incoming.char === " ") return existing
+  if ((existing.style !== "edge" && existing.style !== "activeEdge") || existing.char === " ") return incoming
+  if (DIAGRAM_ARROW_HEADS.has(existing.char) || DIAGRAM_ARROW_HEADS.has(incoming.char)) return incoming
+
+  return {
+    ...incoming,
+    char: mergeDiagramLineGlyph(existing.char, incoming.char, "rounded") ?? incoming.char,
+  } as DiagramCanvasCell<FlowchartCellStyle, FlowchartCellMetadata>
+}
+
+function nodeMetadataForCell(
+  bounds: FlowchartNodeBounds,
+  nodeId: string,
+  x: number,
+  y: number,
+  border = false,
+): FlowchartCellMetadata {
+  const key = flowchartNodeColorKey(nodeId, diagramRadialCellColorLevel(bounds, x, y, border))
+  return { nodeId: key, bgNodeId: key }
+}
+
+function setNodeText(
+  grid: FlowchartGrid,
+  bounds: FlowchartNodeBounds,
+  nodeId: string,
+  x: number,
+  y: number,
+  text: string,
+  style: FlowchartCellStyle,
+): void {
+  grid.setText(x, y, text, style, (cellX, cellY) => nodeMetadataForCell(bounds, nodeId, cellX, cellY))
+}
+
+function fillNodeInterior(
+  grid: FlowchartGrid,
+  bounds: FlowchartNodeBounds,
+  nodeId: string,
+  style: FlowchartCellStyle,
+): void {
+  for (let y = bounds.top + 1; y < bounds.top + bounds.height - 1; y++) {
+    for (let x = bounds.left + 1; x < bounds.left + bounds.width - 1; x++) {
+      grid.setCell(x, y, " ", style, nodeMetadataForCell(bounds, nodeId, x, y))
+    }
+  }
+}
+
+function drawNode(
+  grid: FlowchartGrid,
+  node: FlowchartNode,
+  bounds: FlowchartNodeBounds,
+  borderStyle: BorderStyle,
+  active: boolean,
+): void {
+  const chars = BorderChars[borderStyle]
+  const style: FlowchartCellStyle = active ? "activeNode" : node.shape === "database" ? "database" : "node"
+
+  if (node.shape === "decision") {
+    drawDiagramDiamond(
+      bounds,
+      (x, y, char) => grid.setCell(x, y, char, style, nodeMetadataForCell(bounds, node.id, x, y, true)),
+      diagramDiamondCharactersFromBorder(chars),
+    )
+  } else if (node.shape === "subroutine") {
+    fillNodeInterior(grid, bounds, node.id, style)
+    drawSubroutineNode(grid, bounds, chars, style, node.id)
+  } else if (node.shape === "database") {
+    fillNodeInterior(grid, bounds, node.id, style)
+    drawDatabaseNode(grid, bounds, chars, style, node.id)
+  } else {
+    fillNodeInterior(grid, bounds, node.id, style)
+    drawDiagramFrame(bounds, chars, (x, y, char) =>
+      grid.setCell(x, y, char, style, nodeMetadataForCell(bounds, node.id, x, y, true)),
+    )
+  }
+
+  const textTop =
+    node.shape === "decision"
+      ? bounds.top + Math.floor((bounds.height - bounds.lines.length) / 2)
+      : node.shape === "database"
+        ? bounds.top + 2
+        : bounds.top + 1
+  for (const [index, line] of bounds.lines.entries()) {
+    const lineX =
+      node.shape === "subroutine"
+        ? bounds.left + 3
+        : bounds.left + Math.max(1, Math.floor((bounds.width - visualLength(line)) / 2))
+    setNodeText(grid, bounds, node.id, lineX, textTop + index, line, style)
+  }
+}
+
+function drawSubroutineNode(
+  grid: FlowchartGrid,
+  bounds: FlowchartNodeBounds,
+  chars: BorderCharacters,
+  style: FlowchartCellStyle,
+  nodeId: string,
+): void {
+  drawDiagramFrame(bounds, chars, (x, y, char) =>
+    grid.setCell(x, y, char, style, nodeMetadataForCell(bounds, nodeId, x, y, true)),
+  )
+  const leftRailX = bounds.left + 2
+  const rightRailX = bounds.left + bounds.width - 3
+  grid.setCell(
+    leftRailX,
+    bounds.top,
+    chars.topT,
+    style,
+    nodeMetadataForCell(bounds, nodeId, leftRailX, bounds.top, true),
+  )
+  grid.setCell(
+    rightRailX,
+    bounds.top,
+    chars.topT,
+    style,
+    nodeMetadataForCell(bounds, nodeId, rightRailX, bounds.top, true),
+  )
+  grid.setCell(
+    leftRailX,
+    bounds.top + bounds.height - 1,
+    chars.bottomT,
+    style,
+    nodeMetadataForCell(bounds, nodeId, leftRailX, bounds.top + bounds.height - 1, true),
+  )
+  grid.setCell(
+    rightRailX,
+    bounds.top + bounds.height - 1,
+    chars.bottomT,
+    style,
+    nodeMetadataForCell(bounds, nodeId, rightRailX, bounds.top + bounds.height - 1, true),
+  )
+  for (let y = bounds.top + 1; y < bounds.top + bounds.height - 1; y++) {
+    grid.setCell(leftRailX, y, chars.vertical, style, nodeMetadataForCell(bounds, nodeId, leftRailX, y, true))
+    grid.setCell(rightRailX, y, chars.vertical, style, nodeMetadataForCell(bounds, nodeId, rightRailX, y, true))
+  }
+}
+
+function drawDatabaseNode(
+  grid: FlowchartGrid,
+  bounds: FlowchartNodeBounds,
+  chars: BorderCharacters,
+  style: FlowchartCellStyle,
+  nodeId: string,
+): void {
+  drawDiagramFrame(bounds, chars, (x, y, char) =>
+    grid.setCell(x, y, char, style, nodeMetadataForCell(bounds, nodeId, x, y, true)),
+  )
+  const topRailY = bounds.top + 1
+  const bottomRailY = bounds.top + bounds.height - 2
+  for (const y of [topRailY, bottomRailY]) {
+    grid.setCell(bounds.left, y, chars.leftT, style, nodeMetadataForCell(bounds, nodeId, bounds.left, y, true))
+    grid.setCell(
+      bounds.left + bounds.width - 1,
+      y,
+      chars.rightT,
+      style,
+      nodeMetadataForCell(bounds, nodeId, bounds.left + bounds.width - 1, y, true),
+    )
+    for (let x = bounds.left + 1; x < bounds.left + bounds.width - 1; x++) {
+      grid.setCell(x, y, chars.horizontal, style, nodeMetadataForCell(bounds, nodeId, x, y, true))
+    }
+  }
+}
+
+function drawSubgraphFrame(grid: FlowchartGrid, bounds: FlowchartSubgraphBounds, borderStyle: BorderStyle): void {
+  const chars = BorderChars[borderStyle]
+  drawDiagramFrame(bounds, chars, (x, y, char) => grid.setCell(x, y, char, "group"))
+}
+
+function drawSubgraphLabel(grid: FlowchartGrid, bounds: FlowchartSubgraphBounds): void {
+  if (bounds.label) {
+    const lines = splitDiagramLines(bounds.label)
+    const labelY = bounds.labelSide === "top" ? bounds.top : bounds.top + bounds.height - lines.length
+    for (const [index, line] of lines.entries()) {
+      grid.setText(bounds.left + 2, labelY + index, ` ${line} `, "group")
+    }
+  }
+}
+
+function drawEdgeLabel(grid: FlowchartGrid, route: FlowchartEdgeRoute, style: FlowchartCellStyle): void {
+  const label = flowchartEdgeLabelLayout(route.points, route.edge.label, visualLength)
+  for (const [index, line] of label.lines.entries()) {
+    grid.setText(label.point.x, label.point.y + index, line, style)
+  }
+}
+
+function drawRoutedEdge(grid: FlowchartGrid, route: FlowchartEdgeRoute, active = false): void {
+  const { edge, points } = route
+  if (points.length < 2) return
+  const style: FlowchartCellStyle = active ? "activeEdge" : "edge"
+
+  drawOrthogonalPath(points, (x, y, char) => grid.setCell(x, y, char, style), {
+    cornerStyle: "rounded",
+    lineStyle: edge.style === "thick" ? "heavy" : edge.style === "dashed" ? "dashed" : "single",
+  })
+  const end = points[points.length - 1]!
+  const arrowFrom = points[points.length - 2]!
+  grid.setCell(end.x, end.y, diagramArrowHeadBetween(arrowFrom, end), style)
+  if (edge.label) {
+    drawEdgeLabel(grid, route, active ? "activeEdge" : "label")
+  }
+}
+
+function activeEdgeMatches(
+  route: FlowchartEdgeRoute,
+  edgeIndex: number,
+  activeEdge: FlowchartActiveEdgeSelection,
+): boolean {
+  return (
+    route.edge.from === activeEdge.from &&
+    route.edge.to === activeEdge.to &&
+    (activeEdge.index ?? edgeIndex) === edgeIndex
+  )
+}
+
+function activeRoute(
+  routes: readonly FlowchartEdgeRoute[],
+  diagram: FlowchartDiagram,
+  activeEdge: FlowchartActiveEdgeSelection | undefined,
+): FlowchartEdgeRoute | undefined {
+  if (!activeEdge) return undefined
+  const edgeIndexes = new Map(diagram.edges.map((edge, index) => [edge, index]))
+  for (let index = 0; index < routes.length; index++) {
+    const route = routes[index]!
+    if (activeEdgeMatches(route, edgeIndexes.get(route.edge) ?? index, activeEdge)) return route
+  }
+  return undefined
+}
+
+function activeRoutePoints(
+  route: FlowchartEdgeRoute,
+  from: FlowchartNodeBounds | undefined,
+): readonly FlowchartPoint[] {
+  const sourcePoint = route.points[0]
+  return from && sourcePoint ? [{ ...flowchartSourceConnector(from, sourcePoint) }, ...route.points] : route.points
+}
+
+function styleActivePathCell(grid: FlowchartGrid, x: number, y: number, style: FlowchartCellStyle): void {
+  const cell = grid.getCell(x, y)
+  if (cell && cell.char !== " ") cell.style = style
+}
+
+function drawActiveRoute(grid: FlowchartGrid, route: FlowchartEdgeRoute, from: FlowchartNodeBounds | undefined): void {
+  for (const point of orthogonalPathPoints(activeRoutePoints(route, from))) {
+    styleActivePathCell(grid, point.x, point.y, "activeEdge")
+  }
+  if (route.edge.label) {
+    drawEdgeLabel(grid, route, "activeEdge")
+  }
+}
+
+function flowchartNodeStyle(node: FlowchartNode | undefined): "node" | "database" {
+  return node?.shape === "database" ? "database" : "node"
+}
+
+function sourceFadeStyles(sourceStyle: "node" | "database"): readonly FlowchartEdgeFadeStyle[] {
+  return sourceStyle === "database" ? DATABASE_EDGE_FADE_STYLES : NODE_EDGE_FADE_STYLES
+}
+
+function styleExistingEdgeCell(grid: FlowchartGrid, x: number, y: number, style: FlowchartEdgeFadeStyle): boolean {
+  const cell = grid.getCell(x, y)
+  if (!cell || cell.char === " " || cell.style === "label" || DIAGRAM_ARROW_HEADS.has(cell.char)) return false
+  grid.setCell(x, y, cell.char, style)
+  return true
+}
+
+function fadeSourcePath(
+  grid: FlowchartGrid,
+  points: FlowchartPoint[],
+  styles: readonly FlowchartEdgeFadeStyle[],
+): void {
+  let styleIndex = 1
+  const seen = new Set<string>()
+
+  for (let index = 1; index < points.length && styleIndex < styles.length; index++) {
+    const from = points[index - 1]!
+    const to = points[index]!
+    const direction = flowchartDirectionBetween(from, to)
+    if (!direction) continue
+    walkOrthogonalSegment(from, to, index === 1, (point) => {
+      if (styleIndex >= styles.length) return false
+      const key = `${point.x}:${point.y}`
+      if (!seen.has(key)) {
+        seen.add(key)
+        if (styleExistingEdgeCell(grid, point.x, point.y, styles[styleIndex]!)) styleIndex += 1
+      }
+      return styleIndex < styles.length
+    })
+  }
+}
+
+function drawSourceConnectors(
+  grid: FlowchartGrid,
+  diagram: FlowchartDiagram,
+  bounds: Map<string, FlowchartNodeBounds>,
+  routes: readonly FlowchartEdgeRoute[],
+): void {
+  const nodesById = new Map(diagram.nodes.map((node) => [node.id, node]))
+
+  for (const route of routes) {
+    const from = bounds.get(route.edge.from)
+    const sourcePoint = route.points[0]
+    if (!from || !sourcePoint) continue
+    const styles = sourceFadeStyles(flowchartNodeStyle(nodesById.get(route.edge.from)))
+    const connector = flowchartSourceConnector(from, sourcePoint)
+    grid.setCell(connector.x, connector.y, connector.char, styles[0])
+    const routeDirection = route.points[1] ? flowchartDirectionBetween(sourcePoint, route.points[1]!) : undefined
+    const connectorDirection = flowchartDirectionBetween(sourcePoint, connector)
+    if (routeDirection && connectorDirection) {
+      const cell = grid.getCell(sourcePoint.x, sourcePoint.y)
+      if (cell) {
+        cell.char = diagramLineGlyph(
+          new Set([routeDirection, connectorDirection]),
+          "rounded",
+          route.edge.style === "thick" ? "heavy" : "single",
+        )
+        cell.style = "edge"
+      }
+    }
+    fadeSourcePath(grid, route.points, styles)
+  }
+}
+
+export function drawFlowchartDiagramGrid(
+  diagram: FlowchartDiagram,
+  options: FlowchartDiagramRenderOptions = {},
+): FlowchartGrid {
+  const borderStyle = options.borderStyle ?? DEFAULT_BORDER_STYLE
+  const layout = layoutFlowchartDiagram(diagram, options)
+  const { bounds, routes, subgraphBounds, width, height } = layout
+  diagram = layout.diagram
+  const grid = new DiagramCanvas<FlowchartCellStyle, FlowchartCellMetadata>(width, height, {
+    mergeCell: mergeFlowchartCell,
+  })
+  const selectedRoute = activeRoute(routes, diagram, options.activeEdge)
+
+  for (const subgraph of diagram.subgraphs ?? []) {
+    const bound = subgraphBounds.get(subgraph.id)
+    if (bound) drawSubgraphFrame(grid, bound, borderStyle)
+  }
+  for (const route of routes) drawRoutedEdge(grid, route)
+  for (const node of diagram.nodes) {
+    const bound = bounds.get(node.id)
+    if (bound) drawNode(grid, node, bound, borderStyle, node.id === options.activeNode)
+  }
+  drawSourceConnectors(grid, diagram, bounds, routes)
+  if (selectedRoute) {
+    const from = bounds.get(selectedRoute.edge.from)
+    drawActiveRoute(grid, selectedRoute, from)
+  }
+  for (const subgraph of diagram.subgraphs ?? []) {
+    const bound = subgraphBounds.get(subgraph.id)
+    if (bound) drawSubgraphLabel(grid, bound)
+  }
+
+  return grid
+}

packages/merman/src/flowchart/index.ts

@@ -0,0 +1,43 @@
+import { renderFlowchartDiagram, renderFlowchartDiagramAnsi } from "./render.js"
+import type { FlowchartDiagramAnsiOptions, FlowchartDiagramRenderOptions } from "./options.js"
+
+export type {
+  FlowchartDiagram as Diagram,
+  FlowchartActiveEdgeSelection as ActiveEdgeSelection,
+  FlowchartDirection as Direction,
+  FlowchartEdge as Edge,
+  FlowchartEdgeDirection as EdgeDirection,
+  FlowchartEdgeRoute as EdgeRoute,
+  FlowchartNode as Node,
+  FlowchartNodeBounds as NodeBounds,
+  FlowchartNodeShape as NodeShape,
+  FlowchartPoint as Point,
+  FlowchartSubgraph as Subgraph,
+  FlowchartSubgraphBounds as SubgraphBounds,
+} from "./types.js"
+export type {
+  FlowchartDiagramAnsiOptions as AnsiRenderOptions,
+  FlowchartDiagramOptions as RenderableOptions,
+  FlowchartDiagramRenderOptions as PlainRenderOptions,
+} from "./options.js"
+export type { FlowchartDiagramAnsiTheme as Theme, FlowchartNodeColors as NodeColors } from "./style.js"
+export { flowchartNodeColorKey as nodeColorKey } from "./style.js"
+export { isMermaidFlowchartDiagram as is, parseMermaidFlowchartDiagram as parse } from "./parser.js"
+export { FlowchartDiagramRenderable as Renderable } from "./renderable.js"
+
+export interface RenderOptions extends FlowchartDiagramAnsiOptions {
+  /** Emit ANSI color escapes. Default: `true`. Pass `false` for plain text. */
+  color?: boolean
+}
+
+/**
+ * Render a Mermaid flowchart string for the terminal.
+ *
+ * Defaults to ANSI-colored output. Pass `{ color: false }` for plain text.
+ */
+export function render(content: string, options: RenderOptions = {}): string {
+  const { color = true, ...rest } = options
+  return color
+    ? renderFlowchartDiagramAnsi(content, rest)
+    : renderFlowchartDiagram(content, rest as FlowchartDiagramRenderOptions)
+}

packages/merman/src/flowchart/labels.test.ts

@@ -0,0 +1,111 @@
+import { describe, expect, test } from "bun:test"
+import { flowchartEdgeLabelLayout } from "./labels.js"
+
+const measure = (text: string): number => text.length
+
+describe("flowchart edge labels", () => {
+  test("places vertical-route labels beside the bus", () => {
+    expect(
+      flowchartEdgeLabelLayout(
+        [
+          { x: 22, y: 3 },
+          { x: 22, y: 7 },
+        ],
+        "rollback",
+        measure,
+      ).point,
+    ).toEqual({ x: 23, y: 5 })
+  })
+
+  test("places labels inline only when padded text fits with clearance", () => {
+    expect(
+      flowchartEdgeLabelLayout(
+        [
+          { x: 0, y: 2 },
+          { x: 13, y: 2 },
+        ],
+        "rollback",
+        measure,
+      ).point,
+    ).toEqual({ x: 2, y: 2 })
+
+    expect(
+      flowchartEdgeLabelLayout(
+        [
+          { x: 0, y: 2 },
+          { x: 9, y: 2 },
+        ],
+        "rollback",
+        measure,
+      ).point,
+    ).toEqual({ x: 2, y: 1 })
+
+    expect(
+      flowchartEdgeLabelLayout(
+        [
+          { x: 0, y: 2 },
+          { x: 7, y: 2 },
+        ],
+        "rollback",
+        measure,
+      ).point,
+    ).toEqual({ x: 2, y: 1 })
+  })
+
+  test("uses vertical bus labels before short terminal branches", () => {
+    expect(
+      flowchartEdgeLabelLayout(
+        [
+          { x: 155, y: 5 },
+          { x: 150, y: 5 },
+          { x: 150, y: 9 },
+          { x: 146, y: 9 },
+        ],
+        "rollback",
+        measure,
+      ).point,
+    ).toEqual({ x: 151, y: 7 })
+  })
+
+  test("measures br-delimited edge label lines as a block", () => {
+    const layout = flowchartEdgeLabelLayout(
+      [
+        { x: 0, y: 2 },
+        { x: 20, y: 2 },
+      ],
+      "first<br/>second line",
+      measure,
+    )
+
+    expect(layout.lines).toEqual([" first ", " second line "])
+    expect(layout.width).toBe(13)
+    expect(layout.height).toBe(2)
+  })
+
+  test("places multiline horizontal edge labels outside the route row", () => {
+    const layout = flowchartEdgeLabelLayout(
+      [
+        { x: 0, y: 5 },
+        { x: 20, y: 5 },
+      ],
+      "first<br/>second",
+      measure,
+    )
+
+    expect(layout.point.y + layout.height).toBeLessThanOrEqual(5)
+  })
+
+  test("centers multiline vertical edge labels beside their route", () => {
+    const layout = flowchartEdgeLabelLayout(
+      [
+        { x: 22, y: 2 },
+        { x: 22, y: 10 },
+      ],
+      "one<br/>two<br/>three",
+      measure,
+    )
+
+    expect(layout.point).toEqual({ x: 23, y: 5 })
+    expect(layout.height).toBe(3)
+  })
+})

packages/merman/src/flowchart/labels.ts

@@ -0,0 +1,104 @@
+import {
+  clampPoint,
+  centeredSpanStart,
+  insetSpan,
+  midpoint,
+  point,
+  pointOnSegment,
+  segmentBetween,
+  segmentSpan,
+  shiftPoint,
+  spanCapacity,
+  type DiagramSegment,
+} from "../core/geometry.js"
+import { splitDiagramLines } from "../core/text.js"
+import type { FlowchartPoint } from "./types.js"
+
+const LABEL_BUS_CLEARANCE = 3
+const LABEL_NODE_CLEARANCE = 2
+const LABEL_LINE_CLEARANCE = 2
+const LABEL_PADDING = 1
+
+export interface FlowchartEdgeLabelLayout {
+  lines: string[]
+  point: FlowchartPoint
+  width: number
+  height: number
+}
+
+export function flowchartLabelText(label: string): string {
+  return `${" ".repeat(LABEL_PADDING)}${label}${" ".repeat(LABEL_PADDING)}`
+}
+
+export function flowchartLabelWidth(label: string, measure: (text: string) => number): number {
+  return Math.max(...splitDiagramLines(label).map((line) => measure(line) + LABEL_PADDING * 2))
+}
+
+function minimumInlineLabelLength(labelWidth: number): number {
+  return labelWidth + LABEL_LINE_CLEARANCE * 2 - 1
+}
+
+export function flowchartHorizontalLabelRankGap(labelWidth: number): number {
+  return minimumInlineLabelLength(labelWidth) + LABEL_BUS_CLEARANCE + 1
+}
+
+export function flowchartVerticalBranchLabelGap(labelWidth: number): number {
+  return minimumInlineLabelLength(labelWidth) + LABEL_BUS_CLEARANCE + LABEL_NODE_CLEARANCE
+}
+
+function inlineLabelSlot(segment: DiagramSegment, labelWidth: number): { x: number; fits: boolean } {
+  const slot = insetSpan(segmentSpan(segment), LABEL_LINE_CLEARANCE)
+  return { x: centeredSpanStart(slot, labelWidth), fits: spanCapacity(slot) >= labelWidth }
+}
+
+function segmentLabelPoint(segment: DiagramSegment, labelWidth: number, labelHeight: number): FlowchartPoint {
+  if (segment.axis === "x") {
+    const slot = inlineLabelSlot(segment, labelWidth)
+    if (labelHeight === 1 && slot.fits) return point(slot.x, segment.from.y)
+
+    if (labelHeight > 1) {
+      return shiftPoint(point(slot.x, segment.from.y), "up", labelHeight)
+    }
+
+    return clampPoint(shiftPoint(shiftPoint(segment.from, segment.direction, LABEL_LINE_CLEARANCE), "up", labelHeight))
+  }
+
+  const center = shiftPoint(pointOnSegment(segment, midpoint(segmentSpan(segment))), "right")
+  return clampPoint(shiftPoint(center, "up", Math.floor((labelHeight - 1) / 2)))
+}
+
+function bestLabelSegment(points: readonly FlowchartPoint[], labelWidth: number): DiagramSegment | undefined {
+  let roomyHorizontal: DiagramSegment | undefined
+  let verticalBus: DiagramSegment | undefined
+  let longest: DiagramSegment | undefined
+
+  for (let index = 1; index < points.length; index++) {
+    const segment = segmentBetween(points[index - 1]!, points[index]!)
+    if (!segment) continue
+    if (!roomyHorizontal && segment.axis === "x" && inlineLabelSlot(segment, labelWidth).fits) roomyHorizontal = segment
+    if (!verticalBus && segment.axis === "y") verticalBus = segment
+    if (!longest || segment.length > longest.length) longest = segment
+  }
+
+  return roomyHorizontal ?? verticalBus ?? longest
+}
+
+function flowchartLabelPoint(
+  points: readonly FlowchartPoint[],
+  labelWidth: number,
+  labelHeight: number,
+): FlowchartPoint {
+  const segment = bestLabelSegment(points, labelWidth)
+  return segment ? segmentLabelPoint(segment, labelWidth, labelHeight) : (points[0] ?? point(0, 0))
+}
+
+export function flowchartEdgeLabelLayout(
+  points: readonly FlowchartPoint[],
+  label: string,
+  measure: (text: string) => number,
+): FlowchartEdgeLabelLayout {
+  const lines = splitDiagramLines(label).map(flowchartLabelText)
+  const width = flowchartLabelWidth(label, measure)
+  const height = lines.length
+  return { lines, point: flowchartLabelPoint(points, width, height), width, height }
+}

packages/merman/src/flowchart/layout.ts

@@ -0,0 +1,639 @@
+import {
+  diagramBoundsFromBounds,
+  diagramBoundsFromPoints,
+  segmentBetween,
+  segmentSpan,
+  translateDiagramBounds,
+} from "../core/geometry.js"
+import { diagramTextWidth, measureDiagramTextBox, splitDiagramLines } from "../core/text.js"
+import {
+  flowchartEdgeLabelLayout,
+  flowchartHorizontalLabelRankGap,
+  flowchartLabelWidth,
+  flowchartVerticalBranchLabelGap,
+} from "./labels.js"
+import type { FlowchartDiagramRenderOptions } from "./options.js"
+import { routeFlowchartEdges } from "./routing.js"
+import type {
+  FlowchartDiagram,
+  FlowchartDirection,
+  FlowchartEdge,
+  FlowchartEdgeRoute,
+  FlowchartNode,
+  FlowchartNodeBounds,
+  FlowchartNodeSize,
+  FlowchartSubgraphBounds,
+} from "./types.js"
+
+export const DEFAULT_MIN_NODE_GAP = 5
+export const DEFAULT_MIN_BRANCH_LABEL_GAP = 12
+export const DEFAULT_MIN_RANK_GAP = 10
+export const DEFAULT_MIN_VERTICAL_RANK_GAP = 4
+export const COMPACT_MIN_RANK_GAP = 4
+export const COMPACT_MIN_VERTICAL_RANK_GAP = 2
+const SUBGRAPH_PADDING_X = 2
+const SUBGRAPH_PADDING_TOP = 1
+const SUBGRAPH_PADDING_BOTTOM = 1
+
+export interface FlowchartLayout {
+  diagram: FlowchartDiagram
+  bounds: Map<string, FlowchartNodeBounds>
+  routes: FlowchartEdgeRoute[]
+  subgraphBounds: Map<string, FlowchartSubgraphBounds>
+  width: number
+  height: number
+}
+
+type FlowchartBounds = Pick<FlowchartSubgraphBounds, "left" | "top" | "width" | "height" | "centerX" | "centerY">
+
+function horizontalRankGaps(
+  diagram: FlowchartDiagram,
+  normalizedRanks: ReadonlyMap<string, number>,
+  rankKeys: readonly number[],
+  fallback: number,
+): number[] {
+  const gaps = Array.from({ length: Math.max(0, rankKeys.length - 1) }, () => fallback)
+  const rankIndexes = new Map(rankKeys.map((rank, index) => [rank, index]))
+
+  for (const edge of diagram.edges) {
+    if (!edge.label) continue
+    const fromIndex = rankIndexes.get(normalizedRanks.get(edge.from) ?? -1)
+    const toIndex = rankIndexes.get(normalizedRanks.get(edge.to) ?? -1)
+    if (fromIndex === undefined || toIndex === undefined || fromIndex === toIndex) continue
+
+    const labelGap = flowchartHorizontalLabelRankGap(flowchartLabelWidth(edge.label, visualLength))
+    for (let index = Math.min(fromIndex, toIndex); index < Math.max(fromIndex, toIndex); index++) {
+      gaps[index] = Math.max(gaps[index]!, labelGap)
+    }
+  }
+
+  return gaps
+}
+
+function verticalRankGaps(
+  diagram: FlowchartDiagram,
+  normalizedRanks: ReadonlyMap<string, number>,
+  rankKeys: readonly number[],
+  fallback: number,
+): number[] {
+  const gaps = Array.from({ length: Math.max(0, rankKeys.length - 1) }, () => fallback)
+  const rankIndexes = new Map(rankKeys.map((rank, index) => [rank, index]))
+
+  for (const edge of diagram.edges) {
+    if (!edge.label) continue
+    const fromIndex = rankIndexes.get(normalizedRanks.get(edge.from) ?? -1)
+    const toIndex = rankIndexes.get(normalizedRanks.get(edge.to) ?? -1)
+    if (fromIndex === undefined || toIndex === undefined || fromIndex === toIndex) continue
+
+    const labelHeight = splitDiagramLines(edge.label).length
+    for (let index = Math.min(fromIndex, toIndex); index < Math.max(fromIndex, toIndex); index++) {
+      gaps[index] = Math.max(gaps[index]!, labelHeight + 2)
+    }
+  }
+
+  return gaps
+}
+
+function isHorizontalDirection(direction: FlowchartDirection): boolean {
+  return direction === "LR" || direction === "RL"
+}
+
+export function visualLength(value: string): number {
+  return diagramTextWidth(value)
+}
+
+export function normalizePositiveInt(value: number | undefined, fallback: number): number {
+  if (value === undefined || !Number.isFinite(value)) return fallback
+  return Math.max(1, Math.trunc(value))
+}
+
+function nodeSize(node: FlowchartNode): FlowchartNodeSize {
+  const { lines, width } = measureDiagramTextBox(node.label, { paddingX: 2 })
+  const innerWidth = width - 4
+  if (node.shape === "decision") {
+    const width = innerWidth + 6
+    return {
+      width: width % 2 === 0 ? width + 1 : width,
+      height: Math.max(5, lines.length + 4),
+      lines,
+    }
+  }
+  if (node.shape === "database") return { width: innerWidth + 4, height: lines.length + 4, lines }
+  if (node.shape === "subroutine") return { width: innerWidth + 6, height: lines.length + 2, lines }
+  return { width: innerWidth + 4, height: lines.length + 2, lines }
+}
+
+function rankNodes(diagram: FlowchartDiagram): Map<string, number> {
+  const ranks = new Map<string, number>()
+  const outgoing = new Map<string, string[]>()
+  const incoming = new Set<string>()
+  const incomingCounts = new Map(diagram.nodes.map((node) => [node.id, 0]))
+
+  for (const edge of diagram.edges) {
+    const list = outgoing.get(edge.from) ?? []
+    list.push(edge.to)
+    outgoing.set(edge.from, list)
+    incoming.add(edge.to)
+    incomingCounts.set(edge.to, (incomingCounts.get(edge.to) ?? 0) + 1)
+  }
+
+  const starts = diagram.nodes.filter((node) => !incoming.has(node.id))
+  if (starts.length === 0 && diagram.nodes[0]) starts.push(diagram.nodes[0])
+
+  const queue = starts.map((node) => node.id)
+  for (const node of starts) ranks.set(node.id, 0)
+
+  for (let index = 0; index < queue.length; index++) {
+    const id = queue[index]!
+    const rank = ranks.get(id) ?? 0
+    for (const to of outgoing.get(id) ?? []) {
+      const nextRank = rank + 1
+      if ((ranks.get(to) ?? Number.POSITIVE_INFINITY) <= nextRank) continue
+      ranks.set(to, nextRank)
+      queue.push(to)
+    }
+  }
+
+  for (const node of diagram.nodes) {
+    if (!ranks.has(node.id)) ranks.set(node.id, ranks.size)
+  }
+
+  const acyclicRanks = new Map<string, number>()
+  const acyclicQueue = diagram.nodes.filter((node) => incomingCounts.get(node.id) === 0).map((node) => node.id)
+  for (const id of acyclicQueue) acyclicRanks.set(id, 0)
+  for (let index = 0; index < acyclicQueue.length; index++) {
+    const id = acyclicQueue[index]!
+    const rank = acyclicRanks.get(id) ?? 0
+    for (const to of outgoing.get(id) ?? []) {
+      acyclicRanks.set(to, Math.max(acyclicRanks.get(to) ?? 0, rank + 1))
+      const remainingIncoming = (incomingCounts.get(to) ?? 0) - 1
+      incomingCounts.set(to, remainingIncoming)
+      if (remainingIncoming === 0) acyclicQueue.push(to)
+    }
+  }
+  for (const [id, rank] of acyclicRanks) ranks.set(id, rank)
+
+  return ranks
+}
+
+function translateBounds(bounds: FlowchartBounds, dx: number, dy: number): void {
+  translateDiagramBounds(bounds, dx, dy)
+}
+
+function translateRoutes(routes: readonly FlowchartEdgeRoute[], dx: number, dy: number): void {
+  for (const route of routes) {
+    for (const point of route.points) {
+      point.x += dx
+      point.y += dy
+    }
+  }
+}
+
+function boundsFromChildren(children: readonly FlowchartBounds[]): FlowchartBounds | undefined {
+  return diagramBoundsFromBounds(children)
+}
+
+function subgraphBoundFromChildren(
+  id: string,
+  label: string,
+  children: readonly FlowchartBounds[],
+): FlowchartSubgraphBounds {
+  const labelLines = splitDiagramLines(label)
+  const labelHeight = labelLines.length
+  let left = Math.min(...children.map((child) => child.left)) - SUBGRAPH_PADDING_X
+  const top = Math.min(...children.map((child) => child.top)) - Math.max(SUBGRAPH_PADDING_TOP, labelHeight)
+  let right = Math.max(...children.map((child) => child.left + child.width)) + SUBGRAPH_PADDING_X
+  const bottom =
+    Math.max(...children.map((child) => child.top + child.height)) + Math.max(SUBGRAPH_PADDING_BOTTOM, labelHeight)
+  const minWidth = Math.max(...labelLines.map(visualLength)) + 5
+
+  if (right - left < minWidth) {
+    const extra = minWidth - (right - left)
+    left -= Math.floor(extra / 2)
+    right += Math.ceil(extra / 2)
+  }
+
+  const width = right - left
+  const height = Math.max(3, bottom - top)
+  return {
+    id,
+    label,
+    left,
+    top,
+    width,
+    height,
+    centerX: left + Math.floor(width / 2),
+    centerY: top + Math.floor(height / 2),
+    labelSide: "top",
+  }
+}
+
+function spansOverlap(leftStart: number, leftEnd: number, rightStart: number, rightEnd: number): boolean {
+  return leftStart <= rightEnd && rightStart <= leftEnd
+}
+
+function labelSlot(bounds: FlowchartSubgraphBounds, side: FlowchartSubgraphBounds["labelSide"]): FlowchartBounds {
+  const lines = splitDiagramLines(bounds.label)
+  const left = bounds.left + 2
+  const height = lines.length
+  const top = side === "top" ? bounds.top : bounds.top + bounds.height - height
+  const width = Math.max(...lines.map((line) => visualLength(` ${line} `)))
+  return { left, top, width, height, centerX: left + Math.floor(width / 2), centerY: top + Math.floor(height / 2) }
+}
+
+function segmentOverlapsSlot(
+  from: { x: number; y: number },
+  to: { x: number; y: number },
+  slot: FlowchartBounds,
+): boolean {
+  const segment = segmentBetween(from, to)
+  if (!segment) return false
+
+  const slotRight = slot.left + slot.width - 1
+  const slotBottom = slot.top + slot.height - 1
+  const span = segmentSpan(segment)
+  if (segment.axis === "x") {
+    return (
+      segment.from.y >= slot.top &&
+      segment.from.y <= slotBottom &&
+      spansOverlap(span.start, span.end, slot.left, slotRight)
+    )
+  }
+  return (
+    segment.from.x >= slot.left &&
+    segment.from.x <= slotRight &&
+    spansOverlap(span.start, span.end, slot.top, slotBottom)
+  )
+}
+
+function routeOverlapsSlot(route: FlowchartEdgeRoute, slot: FlowchartBounds): boolean {
+  for (let index = 1; index < route.points.length; index++) {
+    if (segmentOverlapsSlot(route.points[index - 1]!, route.points[index]!, slot)) return true
+  }
+
+  const routeLabelBounds = labelBounds(route)
+  if (
+    !routeLabelBounds ||
+    !spansOverlap(
+      routeLabelBounds.top,
+      routeLabelBounds.top + routeLabelBounds.height - 1,
+      slot.top,
+      slot.top + slot.height - 1,
+    )
+  ) {
+    return false
+  }
+  return spansOverlap(
+    routeLabelBounds.left,
+    routeLabelBounds.left + routeLabelBounds.width - 1,
+    slot.left,
+    slot.left + slot.width - 1,
+  )
+}
+
+function chooseSubgraphLabelSide(
+  bounds: FlowchartSubgraphBounds,
+  routes: readonly FlowchartEdgeRoute[],
+): FlowchartSubgraphBounds["labelSide"] {
+  const topSlot = labelSlot(bounds, "top")
+  if (!routes.some((route) => routeOverlapsSlot(route, topSlot))) return "top"
+
+  const bottomSlot = labelSlot(bounds, "bottom")
+  return routes.some((route) => routeOverlapsSlot(route, bottomSlot)) ? "top" : "bottom"
+}
+
+function pathBounds(points: readonly { x: number; y: number }[]): FlowchartBounds | undefined {
+  return diagramBoundsFromPoints(points)
+}
+
+function labelBounds(route: FlowchartEdgeRoute): FlowchartBounds | undefined {
+  if (!route.edge.label) return undefined
+  const label = flowchartEdgeLabelLayout(route.points, route.edge.label, visualLength)
+  const { point, width, height } = label
+  return {
+    left: point.x,
+    top: point.y,
+    width,
+    height,
+    centerX: point.x + Math.floor(width / 2),
+    centerY: point.y + Math.floor(height / 2),
+  }
+}
+
+function subgraphRouteBounds(subgraphNodeIds: Set<string>, routes: readonly FlowchartEdgeRoute[]): FlowchartBounds[] {
+  return routeRenderBounds(
+    routes.filter((route) => subgraphNodeIds.has(route.edge.from) && subgraphNodeIds.has(route.edge.to)),
+  )
+}
+
+function routeRenderBounds(routes: readonly FlowchartEdgeRoute[]): FlowchartBounds[] {
+  const bounds: FlowchartBounds[] = []
+  for (const route of routes) {
+    const routeBounds = pathBounds(route.points)
+    if (routeBounds) bounds.push(routeBounds)
+    const routeLabelBounds = labelBounds(route)
+    if (routeLabelBounds) bounds.push(routeLabelBounds)
+  }
+  return bounds
+}
+
+function layoutRankedNodes(
+  diagram: FlowchartDiagram,
+  direction: FlowchartDirection,
+  sizes: ReadonlyMap<string, FlowchartNodeSize>,
+  minNodeGap: number,
+  requestedMinRankGap: number,
+): Map<string, FlowchartNodeBounds> {
+  const horizontal = isHorizontalDirection(direction)
+  let widestPaddedEdgeLabel = 0
+  for (const edge of diagram.edges) {
+    if (edge.label)
+      widestPaddedEdgeLabel = Math.max(widestPaddedEdgeLabel, flowchartLabelWidth(edge.label, visualLength))
+  }
+  const rankNodeGap = horizontal
+    ? minNodeGap
+    : Math.max(minNodeGap, DEFAULT_MIN_BRANCH_LABEL_GAP, flowchartVerticalBranchLabelGap(widestPaddedEdgeLabel))
+  const ranks = rankNodes(diagram)
+  const maxRank = Math.max(0, ...ranks.values())
+  const ranksByIndex = new Map<number, FlowchartNode[]>()
+  const normalizedRanks = new Map<string, number>()
+
+  for (const node of diagram.nodes) {
+    const rank = ranks.get(node.id) ?? 0
+    const normalizedRank = direction === "RL" || direction === "BT" ? maxRank - rank : rank
+    normalizedRanks.set(node.id, normalizedRank)
+    const nodes = ranksByIndex.get(normalizedRank) ?? []
+    nodes.push(node)
+    ranksByIndex.set(normalizedRank, nodes)
+  }
+
+  const rankKeys = [...ranksByIndex.keys()].sort((a, b) => a - b)
+  const horizontalGaps = horizontal ? horizontalRankGaps(diagram, normalizedRanks, rankKeys, requestedMinRankGap) : []
+  const verticalGaps = horizontal ? [] : verticalRankGaps(diagram, normalizedRanks, rankKeys, requestedMinRankGap)
+  const bounds = new Map<string, FlowchartNodeBounds>()
+
+  if (horizontal) {
+    const columnWidths = rankKeys.map((rank) =>
+      Math.max(...ranksByIndex.get(rank)!.map((node) => sizes.get(node.id)!.width)),
+    )
+    const columnHeights = rankKeys.map((rank) => {
+      const nodes = ranksByIndex.get(rank)!
+      return (
+        nodes.reduce((total, node) => total + sizes.get(node.id)!.height, 0) +
+        Math.max(0, nodes.length - 1) * rankNodeGap
+      )
+    })
+    const canvasHeight = Math.max(1, ...columnHeights)
+    let x = 0
+    for (let rankIndex = 0; rankIndex < rankKeys.length; rankIndex++) {
+      const rank = rankKeys[rankIndex]!
+      const nodes = ranksByIndex.get(rank)!
+      const columnWidth = columnWidths[rankIndex]!
+      let y = Math.floor((canvasHeight - columnHeights[rankIndex]!) / 2)
+      for (const node of nodes) {
+        const size = sizes.get(node.id)!
+        const left = x + Math.floor((columnWidth - size.width) / 2)
+        bounds.set(node.id, {
+          id: node.id,
+          ...size,
+          left,
+          top: y,
+          centerX: left + Math.floor(size.width / 2),
+          centerY: y + Math.floor(size.height / 2),
+        })
+        y += size.height + rankNodeGap
+      }
+      x += columnWidth + (horizontalGaps[rankIndex] ?? 0)
+    }
+  } else {
+    const rowHeights = rankKeys.map((rank) =>
+      Math.max(...ranksByIndex.get(rank)!.map((node) => sizes.get(node.id)!.height)),
+    )
+    const rowWidths = rankKeys.map((rank) => {
+      const nodes = ranksByIndex.get(rank)!
+      return (
+        nodes.reduce((total, node) => total + sizes.get(node.id)!.width, 0) +
+        Math.max(0, nodes.length - 1) * rankNodeGap
+      )
+    })
+    const canvasWidth = Math.max(1, ...rowWidths)
+    let y = 0
+    for (let rankIndex = 0; rankIndex < rankKeys.length; rankIndex++) {
+      const rank = rankKeys[rankIndex]!
+      const nodes = ranksByIndex.get(rank)!
+      const rowHeight = rowHeights[rankIndex]!
+      let x = Math.floor((canvasWidth - rowWidths[rankIndex]!) / 2)
+      for (const node of nodes) {
+        const size = sizes.get(node.id)!
+        const top = y + Math.floor((rowHeight - size.height) / 2)
+        bounds.set(node.id, {
+          id: node.id,
+          ...size,
+          left: x,
+          top,
+          centerX: x + Math.floor(size.width / 2),
+          centerY: top + Math.floor(size.height / 2),
+        })
+        x += size.width + rankNodeGap
+      }
+      y += rowHeight + (verticalGaps[rankIndex] ?? 0)
+    }
+  }
+
+  return bounds
+}
+
+function layoutLocalSubgraphDirections(
+  diagram: FlowchartDiagram,
+  nodeBounds: Map<string, FlowchartNodeBounds>,
+  sizes: ReadonlyMap<string, FlowchartNodeSize>,
+  minNodeGap: number,
+  requestedMinRankGap: number,
+): void {
+  for (const subgraph of [...(diagram.subgraphs ?? [])].reverse()) {
+    if (!subgraph.direction || subgraph.direction === diagram.direction) continue
+    const nodeIds = new Set(subgraph.nodeIds)
+    const nodes = diagram.nodes.filter((node) => nodeIds.has(node.id))
+    if (nodes.length === 0) continue
+
+    const currentBounds = boundsFromChildren(nodes.flatMap((node) => nodeBounds.get(node.id) ?? []))
+    if (!currentBounds) continue
+
+    const localDiagram: FlowchartDiagram = {
+      direction: subgraph.direction,
+      nodes,
+      edges: diagram.edges.filter((edge) => nodeIds.has(edge.from) && nodeIds.has(edge.to)),
+      subgraphs: [],
+    }
+    const localNodeGap = isHorizontalDirection(subgraph.direction) ? Math.max(4, minNodeGap - 1) : minNodeGap
+    const localBounds = layoutRankedNodes(localDiagram, subgraph.direction, sizes, localNodeGap, requestedMinRankGap)
+    const localExtent = boundsFromChildren([...localBounds.values()])
+    if (!localExtent) continue
+
+    const targetLeft = currentBounds.left + Math.floor((currentBounds.width - localExtent.width) / 2)
+    const targetTop = currentBounds.top + Math.floor((currentBounds.height - localExtent.height) / 2)
+    const dx = targetLeft - localExtent.left
+    const dy = targetTop - localExtent.top
+
+    for (const [nodeId, bound] of localBounds) {
+      translateBounds(bound, dx, dy)
+      nodeBounds.set(nodeId, bound)
+    }
+  }
+}
+
+function edgeDirection(diagram: FlowchartDiagram, edge: FlowchartEdge): FlowchartDirection {
+  for (const subgraph of [...(diagram.subgraphs ?? [])].reverse()) {
+    if (!subgraph.direction) continue
+    if (subgraph.nodeIds.includes(edge.from) && subgraph.nodeIds.includes(edge.to)) return subgraph.direction
+  }
+  return diagram.direction
+}
+
+function hasLocalSubgraphDirection(diagram: FlowchartDiagram): boolean {
+  return (diagram.subgraphs ?? []).some((subgraph) => subgraph.direction && subgraph.direction !== diagram.direction)
+}
+
+function collectSubgraphNodeIds(diagram: FlowchartDiagram, subgraphId: string): Set<string> {
+  const nodeIds = new Set<string>()
+  for (const subgraph of diagram.subgraphs ?? []) {
+    if (subgraph.id !== subgraphId && subgraph.parentId !== subgraphId) continue
+    for (const nodeId of subgraph.nodeIds) nodeIds.add(nodeId)
+    if (subgraph.parentId === subgraphId) {
+      for (const nodeId of collectSubgraphNodeIds(diagram, subgraph.id)) nodeIds.add(nodeId)
+    }
+  }
+  return nodeIds
+}
+
+function separateLocalSubgraphItems(
+  diagram: FlowchartDiagram,
+  nodeBounds: Map<string, FlowchartNodeBounds>,
+  subgraphBounds: ReadonlyMap<string, FlowchartSubgraphBounds>,
+  gap: number,
+): void {
+  if (!hasLocalSubgraphDirection(diagram)) return
+
+  const coveredNodeIds = new Set<string>()
+  const items: { bounds: FlowchartBounds; nodeIds: Set<string> }[] = []
+  for (const subgraph of diagram.subgraphs ?? []) {
+    if (subgraph.parentId) continue
+    const bounds = subgraphBounds.get(subgraph.id)
+    const nodeIds = collectSubgraphNodeIds(diagram, subgraph.id)
+    if (!bounds || nodeIds.size === 0) continue
+    items.push({ bounds, nodeIds })
+    for (const nodeId of nodeIds) coveredNodeIds.add(nodeId)
+  }
+
+  for (const node of diagram.nodes) {
+    if (coveredNodeIds.has(node.id)) continue
+    const bounds = nodeBounds.get(node.id)
+    if (bounds) items.push({ bounds, nodeIds: new Set([node.id]) })
+  }
+
+  const horizontal = isHorizontalDirection(diagram.direction)
+  items.sort((a, b) => (horizontal ? a.bounds.left - b.bounds.left : a.bounds.top - b.bounds.top))
+
+  let cursor: number | undefined
+  for (const item of items) {
+    const start = horizontal ? item.bounds.left : item.bounds.top
+    const size = horizontal ? item.bounds.width : item.bounds.height
+    if (cursor === undefined) {
+      cursor = start + size + gap
+      continue
+    }
+    const shift = cursor - start
+    if (shift !== 0) {
+      for (const nodeId of item.nodeIds) {
+        const bounds = nodeBounds.get(nodeId)
+        if (bounds) translateBounds(bounds, horizontal ? shift : 0, horizontal ? 0 : shift)
+      }
+    }
+    cursor = start + shift + size + gap
+  }
+}
+
+function layoutSubgraphs(
+  diagram: FlowchartDiagram,
+  nodeBounds: Map<string, FlowchartNodeBounds>,
+  routes: readonly FlowchartEdgeRoute[],
+): Map<string, FlowchartSubgraphBounds> {
+  const subgraphBounds = new Map<string, FlowchartSubgraphBounds>()
+  const subgraphs = diagram.subgraphs ?? []
+
+  for (const subgraph of [...subgraphs].reverse()) {
+    const children: FlowchartBounds[] = []
+    for (const nodeId of subgraph.nodeIds) {
+      const bound = nodeBounds.get(nodeId)
+      if (bound) children.push(bound)
+    }
+    children.push(...subgraphRouteBounds(new Set(subgraph.nodeIds), routes))
+    for (const childSubgraph of subgraphs) {
+      if (childSubgraph.parentId !== subgraph.id) continue
+      const bound = subgraphBounds.get(childSubgraph.id)
+      if (bound) children.push(bound)
+    }
+    if (children.length > 0) {
+      const bound = subgraphBoundFromChildren(subgraph.id, subgraph.label, children)
+      bound.labelSide = chooseSubgraphLabelSide(bound, routes)
+      subgraphBounds.set(subgraph.id, bound)
+    }
+  }
+
+  return subgraphBounds
+}
+
+function layoutFlowchartWithDirection(
+  sourceDiagram: FlowchartDiagram,
+  options: FlowchartDiagramRenderOptions,
+  direction: FlowchartDirection,
+): FlowchartLayout {
+  const diagram = direction === sourceDiagram.direction ? sourceDiagram : { ...sourceDiagram, direction }
+  const horizontal = isHorizontalDirection(direction)
+  const minNodeGap = normalizePositiveInt(options.minNodeGap, DEFAULT_MIN_NODE_GAP)
+  const requestedMinRankGap = normalizePositiveInt(
+    options.minRankGap,
+    options.compact
+      ? horizontal
+        ? COMPACT_MIN_RANK_GAP
+        : COMPACT_MIN_VERTICAL_RANK_GAP
+      : horizontal
+        ? DEFAULT_MIN_RANK_GAP
+        : DEFAULT_MIN_VERTICAL_RANK_GAP,
+  )
+  const sizes = new Map(diagram.nodes.map((node) => [node.id, nodeSize(node)]))
+  const bounds = layoutRankedNodes(diagram, direction, sizes, minNodeGap, requestedMinRankGap)
+  layoutLocalSubgraphDirections(diagram, bounds, sizes, minNodeGap, requestedMinRankGap)
+
+  let routes = routeFlowchartEdges(diagram, bounds, (edge) => edgeDirection(diagram, edge))
+  let subgraphBounds = layoutSubgraphs(diagram, bounds, routes)
+  separateLocalSubgraphItems(diagram, bounds, subgraphBounds, Math.max(1, Math.floor(requestedMinRankGap / 2)))
+  routes = routeFlowchartEdges(diagram, bounds, (edge) => edgeDirection(diagram, edge))
+  subgraphBounds = layoutSubgraphs(diagram, bounds, routes)
+  routes = routeFlowchartEdges(diagram, bounds, (edge) => edgeDirection(diagram, edge), subgraphBounds)
+  subgraphBounds = layoutSubgraphs(diagram, bounds, routes)
+  const allBounds = [...bounds.values(), ...subgraphBounds.values(), ...routeRenderBounds(routes)]
+  const dx = Math.max(0, -Math.min(0, ...allBounds.map((bound) => bound.left)))
+  const dy = Math.max(0, -Math.min(0, ...allBounds.map((bound) => bound.top)))
+  if (dx > 0 || dy > 0) {
+    for (const bound of allBounds) translateBounds(bound, dx, dy)
+    translateRoutes(routes, dx, dy)
+  }
+
+  const maxX = Math.max(0, ...allBounds.map((bound) => bound.left + bound.width))
+  const maxY = Math.max(0, ...allBounds.map((bound) => bound.top + bound.height))
+  return { diagram, bounds, routes, subgraphBounds, width: maxX + 4, height: maxY + 4 }
+}
+
+export function layoutFlowchartDiagram(
+  sourceDiagram: FlowchartDiagram,
+  options: FlowchartDiagramRenderOptions = {},
+): FlowchartLayout {
+  const direction = options.direction ?? sourceDiagram.direction
+  const layout = layoutFlowchartWithDirection(sourceDiagram, options, direction)
+  const maxWidth = options.layoutMaxWidth
+  if (!isHorizontalDirection(direction) || maxWidth === undefined || !Number.isFinite(maxWidth)) return layout
+  if (layout.width <= Math.max(1, Math.trunc(maxWidth))) return layout
+
+  return layoutFlowchartWithDirection(sourceDiagram, options, direction === "RL" ? "BT" : "TD")
+}

packages/merman/src/flowchart/options.ts

@@ -0,0 +1,32 @@
+import type { BorderStyle, ColorInput, TextBufferOptions } from "@opentui/core"
+import type { FlowchartDiagramAnsiTheme, FlowchartNodeColors } from "./style.js"
+import type { FlowchartActiveEdgeSelection, FlowchartDirection } from "./types.js"
+
+export interface FlowchartDiagramRenderOptions {
+  compact?: boolean
+  direction?: FlowchartDirection
+  borderStyle?: BorderStyle
+  minNodeGap?: number
+  minRankGap?: number
+  /** Fold oversized horizontal layouts vertically when their rendered width exceeds this limit. */
+  layoutMaxWidth?: number
+  activeNode?: string
+  activeEdge?: FlowchartActiveEdgeSelection
+}
+
+export interface FlowchartDiagramAnsiOptions extends FlowchartDiagramRenderOptions {
+  theme?: FlowchartDiagramAnsiTheme
+}
+
+export interface FlowchartDiagramOptions extends TextBufferOptions, FlowchartDiagramRenderOptions {
+  content?: string
+  nodeColor?: ColorInput
+  nodeColors?: FlowchartNodeColors
+  nodeBgColors?: FlowchartNodeColors
+  databaseColor?: ColorInput
+  edgeColor?: ColorInput
+  activeNodeColor?: ColorInput
+  activeEdgeColor?: ColorInput
+  labelColor?: ColorInput
+  groupColor?: ColorInput
+}

packages/merman/src/flowchart/parser.ts

@@ -0,0 +1,215 @@
+import type {
+  FlowchartDiagram,
+  FlowchartDirection,
+  FlowchartEdge,
+  FlowchartEdgeStyle,
+  FlowchartNode,
+  FlowchartSubgraph,
+} from "./types.js"
+import { MermaidSyntaxError } from "../diagnostics.js"
+import {
+  firstMeaningfulMermaidLine,
+  meaningfulNumberedMermaidLines,
+  stripMermaidQuotes as stripQuotes,
+} from "../core/mermaid.js"
+
+const DEFAULT_DIRECTION = "TD" satisfies FlowchartDirection
+const FLOWCHART_HEADER_RE = /^(flowchart|graph)(?:\s+(TB|TD|BT|LR|RL))?$/i
+const ID_RE = "[A-Za-z_][A-Za-z0-9_.-]*"
+const SUBGRAPH_RE = /^subgraph\s+(.+)$/i
+const SUBGRAPH_WITH_LABEL_RE = new RegExp(`^(${ID_RE})\\s*\\[(.+)\\]$`)
+const SUBGRAPH_DIRECTION_RE = /^direction\s+(TB|TD|BT|LR|RL)$/i
+const IGNORED_PRESENTATION_RE = /^(?:classDef|class|style|linkStyle)\b/i
+const DATABASE_NODE_RE = new RegExp(`^(${ID_RE})\\[\\((.+)\\)\\]$`)
+const SUBROUTINE_NODE_RE = new RegExp(`^(${ID_RE})\\[\\[(.+)\\]\\]$`)
+const ROUNDED_BRACKET_NODE_RE = new RegExp(`^(${ID_RE})\\(\\[(.+)\\]\\)$`)
+const ROUNDED_NODE_RE = new RegExp(`^(${ID_RE})\\((.+)\\)$`)
+const DECISION_NODE_RE = new RegExp(`^(${ID_RE})\\{(.+)\\}$`)
+const BOX_NODE_RE = new RegExp(`^(${ID_RE})\\[(.+)\\]$`)
+const ID_ONLY_RE = new RegExp(`^${ID_RE}$`)
+const EXPLICIT_NODE_SHAPE_RE = new RegExp(`^${ID_RE}(?:\\[|\\(|\\{)`)
+
+function normalizeDirection(value?: string): FlowchartDirection {
+  const upper = value?.toUpperCase()
+  if (upper === "TB" || upper === "TD" || upper === "BT" || upper === "LR" || upper === "RL") return upper
+  return DEFAULT_DIRECTION
+}
+
+function normalizeSubgraphId(value: string, index: number): string {
+  const stripped = stripQuotes(value)
+  return ID_ONLY_RE.test(stripped) ? stripped : `subgraph_${index + 1}`
+}
+
+function parseSubgraphToken(token: string, index: number): Pick<FlowchartSubgraph, "id" | "label"> {
+  const trimmed = token
+    .trim()
+    .replace(/\s*:::.*$/, "")
+    .replace(/;$/, "")
+  const withLabel = trimmed.match(SUBGRAPH_WITH_LABEL_RE)
+  if (withLabel) {
+    return { id: withLabel[1]!, label: stripQuotes(withLabel[2]!) }
+  }
+
+  const label = stripQuotes(trimmed)
+  return { id: normalizeSubgraphId(trimmed, index), label }
+}
+
+function parseNodeToken(token: string): FlowchartNode {
+  const trimmed = token.trim().replace(/;$/, "")
+  const database = trimmed.match(DATABASE_NODE_RE)
+  if (database) return { id: database[1]!, label: stripQuotes(database[2]!), shape: "database" }
+
+  const subroutine = trimmed.match(SUBROUTINE_NODE_RE)
+  if (subroutine) return { id: subroutine[1]!, label: stripQuotes(subroutine[2]!), shape: "subroutine" }
+
+  const roundedBracket = trimmed.match(ROUNDED_BRACKET_NODE_RE)
+  if (roundedBracket) return { id: roundedBracket[1]!, label: stripQuotes(roundedBracket[2]!), shape: "rounded" }
+
+  const rounded = trimmed.match(ROUNDED_NODE_RE)
+  if (rounded) return { id: rounded[1]!, label: stripQuotes(rounded[2]!), shape: "rounded" }
+
+  const decision = trimmed.match(DECISION_NODE_RE)
+  if (decision) return { id: decision[1]!, label: stripQuotes(decision[2]!), shape: "decision" }
+
+  const box = trimmed.match(BOX_NODE_RE)
+  if (box) return { id: box[1]!, label: stripQuotes(box[2]!), shape: "box" }
+
+  return { id: trimmed, label: trimmed, shape: "box" }
+}
+
+function hasExplicitNodeShape(token: string): boolean {
+  return EXPLICIT_NODE_SHAPE_RE.test(token.trim())
+}
+
+function ensureNode(nodes: Map<string, FlowchartNode>, token: string): FlowchartNode {
+  const node = parseNodeToken(token)
+  const existing = nodes.get(node.id)
+  if (!existing) {
+    nodes.set(node.id, node)
+    return node
+  }
+
+  if (hasExplicitNodeShape(token)) {
+    existing.label = node.label
+    existing.shape = node.shape
+  }
+  return existing
+}
+
+function addNodeToSubgraph(subgraph: FlowchartSubgraph | undefined, nodeId: string): void {
+  if (!subgraph || subgraph.nodeIds.includes(nodeId)) return
+  subgraph.nodeIds.push(nodeId)
+}
+
+function stripNodeToken(token: string): string {
+  return token
+    .replace(/\s*:::.*$/, "")
+    .replace(/;$/, "")
+    .trim()
+}
+
+function edgeStyleFromArrow(...arrows: string[]): FlowchartEdgeStyle | undefined {
+  if (arrows.some((arrow) => arrow.includes("=="))) return "thick"
+  if (arrows.some((arrow) => arrow.includes("."))) return "dashed"
+  return undefined
+}
+
+function createEdge(from: string, to: string, label: string, style: FlowchartEdgeStyle | undefined): FlowchartEdge {
+  return style ? { from, to, label, style } : { from, to, label }
+}
+
+export function isMermaidFlowchartDiagram(content: string): boolean {
+  return FLOWCHART_HEADER_RE.test(firstMeaningfulMermaidLine(content) ?? "")
+}
+
+export function parseMermaidFlowchartDiagram(content: string): FlowchartDiagram {
+  const nodes = new Map<string, FlowchartNode>()
+  const edges: FlowchartEdge[] = []
+  const subgraphs: FlowchartSubgraph[] = []
+  const subgraphStack: Array<{ subgraph: FlowchartSubgraph; lineNumber: number; sourceLine: string }> = []
+  let direction: FlowchartDirection = DEFAULT_DIRECTION
+
+  for (const source of meaningfulNumberedMermaidLines(content)) {
+    const line = source.text
+    const header = line.match(FLOWCHART_HEADER_RE)
+    if (header) {
+      direction = normalizeDirection(header[2])
+      continue
+    }
+
+    // Mermaid CSS styling does not apply to terminal theme rendering.
+    if (IGNORED_PRESENTATION_RE.test(line)) continue
+
+    const subgraphMatch = line.match(SUBGRAPH_RE)
+    if (subgraphMatch) {
+      const parsed = parseSubgraphToken(subgraphMatch[1]!, subgraphs.length)
+      const subgraph: FlowchartSubgraph = {
+        ...parsed,
+        nodeIds: [],
+        parentId: subgraphStack[subgraphStack.length - 1]?.subgraph.id,
+      }
+      subgraphs.push(subgraph)
+      subgraphStack.push({ subgraph, lineNumber: source.lineNumber, sourceLine: line })
+      continue
+    }
+
+    if (/^end$/i.test(line)) {
+      if (subgraphStack.length === 0) {
+        throw new MermaidSyntaxError("flowchart", source.lineNumber, line, 'Unexpected "end" without an open subgraph')
+      }
+      subgraphStack.pop()
+      continue
+    }
+
+    const currentSubgraph = subgraphStack[subgraphStack.length - 1]?.subgraph
+
+    const subgraphDirection = line.match(SUBGRAPH_DIRECTION_RE)
+    if (subgraphDirection) {
+      if (!currentSubgraph) {
+        throw new MermaidSyntaxError(
+          "flowchart",
+          source.lineNumber,
+          line,
+          'A "direction" statement requires an open subgraph',
+        )
+      }
+      currentSubgraph.direction = normalizeDirection(subgraphDirection[1])
+      continue
+    }
+
+    const pipeEdge = line.match(/^(.+?)\s*(-->|==>|-\.->)\s*(?:\|([^|]*)\|\s*)?(.+)$/)
+    const textEdge = line.match(/^(.+?)\s*(--|==|-\.)\s+(.+?)\s+(-->|==>|\.->|-\.->)\s*(.+)$/)
+    const edgeMatch = textEdge ?? pipeEdge
+    if (edgeMatch) {
+      const from = ensureNode(nodes, stripNodeToken(edgeMatch[1]!))
+      const toToken = textEdge ? edgeMatch[5]! : edgeMatch[4]!
+      const to = ensureNode(nodes, stripNodeToken(toToken))
+      addNodeToSubgraph(currentSubgraph, from.id)
+      addNodeToSubgraph(currentSubgraph, to.id)
+      const arrow = textEdge ? edgeMatch[4]! : edgeMatch[2]!
+      const label = textEdge ? edgeMatch[3]! : (edgeMatch[3] ?? "")
+      edges.push(createEdge(from.id, to.id, label.trim(), edgeStyleFromArrow(textEdge ? edgeMatch[2]! : arrow, arrow)))
+      continue
+    }
+
+    if (hasExplicitNodeShape(line)) {
+      const node = ensureNode(nodes, line)
+      addNodeToSubgraph(currentSubgraph, node.id)
+      continue
+    }
+
+    throw new MermaidSyntaxError("flowchart", source.lineNumber, line)
+  }
+
+  const unclosedSubgraph = subgraphStack[subgraphStack.length - 1]
+  if (unclosedSubgraph) {
+    throw new MermaidSyntaxError(
+      "flowchart",
+      unclosedSubgraph.lineNumber,
+      unclosedSubgraph.sourceLine,
+      'Unclosed subgraph; expected "end"',
+    )
+  }
+
+  return { direction, nodes: [...nodes.values()], edges, subgraphs }
+}

packages/merman/src/flowchart/render.ts

@@ -0,0 +1,15 @@
+import { drawFlowchartDiagramGrid } from "./drawing.js"
+import type { FlowchartDiagramAnsiOptions, FlowchartDiagramRenderOptions } from "./options.js"
+import { parseMermaidFlowchartDiagram } from "./parser.js"
+import { renderGridAnsi } from "./style.js"
+
+export function renderFlowchartDiagram(content: string, options: FlowchartDiagramRenderOptions = {}): string {
+  return drawFlowchartDiagramGrid(parseMermaidFlowchartDiagram(content), options).toString({
+    trimTop: true,
+    trimBottom: true,
+  })
+}
+
+export function renderFlowchartDiagramAnsi(content: string, options: FlowchartDiagramAnsiOptions = {}): string {
+  return renderGridAnsi(drawFlowchartDiagramGrid(parseMermaidFlowchartDiagram(content), options), options.theme)
+}

packages/merman/src/flowchart/renderable.ts

@@ -0,0 +1,269 @@
+import { RGBA, type BorderStyle, type ColorInput, type RenderContext } from "@opentui/core"
+import { DiagramRenderable } from "../core/adapter/diagram-renderable.js"
+import { parseDiagramRenderableColor } from "../core/adapter/renderable-color.js"
+import { diagramColorMapsEqual, normalizeDiagramColorMap } from "../core/color/map.js"
+import { DEFAULT_BORDER_STYLE, drawFlowchartDiagramGrid } from "./drawing.js"
+import type { FlowchartDiagramRenderOptions, FlowchartDiagramOptions } from "./options.js"
+import { parseMermaidFlowchartDiagram } from "./parser.js"
+import {
+  renderGridStyledText,
+  resolveFlowchartStyleColors,
+  type FlowchartGrid,
+  type FlowchartNodeColors,
+} from "./style.js"
+import type { FlowchartActiveEdgeSelection, FlowchartDiagram, FlowchartDirection, FlowchartEdge } from "./types.js"
+
+interface IndexedFlowchartEdge {
+  edge: FlowchartEdge
+  index: number
+}
+
+function flowchartActiveEdgesEqual(
+  left: FlowchartActiveEdgeSelection | undefined,
+  right: FlowchartActiveEdgeSelection | undefined,
+): boolean {
+  return left?.from === right?.from && left?.to === right?.to && left?.index === right?.index
+}
+
+export class FlowchartDiagramRenderable extends DiagramRenderable<FlowchartDiagram, FlowchartGrid> {
+  private _compact: boolean
+  private _direction?: FlowchartDirection
+  private _borderStyle: BorderStyle
+  private _minNodeGap?: number
+  private _minRankGap?: number
+  private _layoutMaxWidth?: number
+  private _nodeColor?: RGBA
+  private _databaseColor?: RGBA
+  private _edgeColor?: RGBA
+  private _activeNodeColor?: RGBA
+  private _activeEdgeColor?: RGBA
+  private _nodeColors: Map<string, RGBA>
+  private _nodeBgColors: Map<string, RGBA>
+  private _labelColor?: RGBA
+  private _groupColor?: RGBA
+  private _activeNode?: string
+  private _activeEdge?: FlowchartActiveEdgeSelection
+  private _selectedConnectionIndex = 0
+  constructor(ctx: RenderContext, options: FlowchartDiagramOptions = {}) {
+    super(ctx, options)
+    this._compact = options.compact ?? false
+    this._direction = options.direction
+    this._borderStyle = options.borderStyle ?? DEFAULT_BORDER_STYLE
+    this._minNodeGap = options.minNodeGap
+    this._minRankGap = options.minRankGap
+    this._layoutMaxWidth = options.layoutMaxWidth
+    this._nodeColor = parseDiagramRenderableColor(options.nodeColor)
+    this._databaseColor = parseDiagramRenderableColor(options.databaseColor)
+    this._edgeColor = parseDiagramRenderableColor(options.edgeColor)
+    this._activeNodeColor = parseDiagramRenderableColor(options.activeNodeColor)
+    this._activeEdgeColor = parseDiagramRenderableColor(options.activeEdgeColor)
+    this._nodeColors = normalizeDiagramColorMap(options.nodeColors)
+    this._nodeBgColors = normalizeDiagramColorMap(options.nodeBgColors)
+    this._labelColor = parseDiagramRenderableColor(options.labelColor)
+    this._groupColor = parseDiagramRenderableColor(options.groupColor)
+    this._activeNode = options.activeNode
+    this._activeEdge = options.activeEdge
+    this.initializeDiagram({
+      parse: () => parseMermaidFlowchartDiagram(this.content),
+      draw: (diagram) => drawFlowchartDiagramGrid(diagram, this.renderOptions()),
+      publish: (grid) => this.styledText(grid),
+      measure: { trimTop: true, trimBottom: true },
+    })
+  }
+
+  protected override contentChanged(): void {
+    this._activeNode = undefined
+    this._activeEdge = undefined
+    this._selectedConnectionIndex = 0
+  }
+
+  get compact(): boolean {
+    return this._compact
+  }
+
+  set compact(value: boolean) {
+    if (this._compact === value) return
+    this._compact = value
+    this.invalidateGrid()
+  }
+
+  set direction(value: FlowchartDirection | undefined) {
+    if (this._direction === value) return
+    this._direction = value
+    this.invalidateGrid()
+  }
+
+  set borderStyle(value: BorderStyle | undefined) {
+    const next = value ?? DEFAULT_BORDER_STYLE
+    if (this._borderStyle === next) return
+    this._borderStyle = next
+    this.invalidateGrid()
+  }
+
+  get layoutMaxWidth(): number | undefined {
+    return this._layoutMaxWidth
+  }
+
+  set layoutMaxWidth(value: number | undefined) {
+    if (this._layoutMaxWidth === value) return
+    this._layoutMaxWidth = value
+    this.invalidateGrid()
+  }
+
+  set nodeColor(value: ColorInput | undefined) {
+    this.setColor(this._nodeColor, value, (color) => (this._nodeColor = color))
+  }
+
+  set databaseColor(value: ColorInput | undefined) {
+    this.setColor(this._databaseColor, value, (color) => (this._databaseColor = color))
+  }
+
+  set edgeColor(value: ColorInput | undefined) {
+    this.setColor(this._edgeColor, value, (color) => (this._edgeColor = color))
+  }
+
+  set activeNodeColor(value: ColorInput | undefined) {
+    this.setColor(this._activeNodeColor, value, (color) => (this._activeNodeColor = color))
+  }
+
+  set activeEdgeColor(value: ColorInput | undefined) {
+    this.setColor(this._activeEdgeColor, value, (color) => (this._activeEdgeColor = color))
+  }
+
+  set nodeColors(value: FlowchartNodeColors | undefined) {
+    const next = normalizeDiagramColorMap(value)
+    if (diagramColorMapsEqual(this._nodeColors, next)) return
+    this._nodeColors = next
+    this.invalidateStyle()
+  }
+
+  set nodeBgColors(value: FlowchartNodeColors | undefined) {
+    const next = normalizeDiagramColorMap(value)
+    if (diagramColorMapsEqual(this._nodeBgColors, next)) return
+    this._nodeBgColors = next
+    this.invalidateStyle()
+  }
+
+  get activeNode(): string | undefined {
+    return this._activeNode
+  }
+
+  set activeNode(value: string | undefined) {
+    if (this._activeNode === value) return
+    this._activeNode = value
+    this._activeEdge = undefined
+    this._selectedConnectionIndex = 0
+    this.invalidateGrid()
+  }
+
+  get selectedConnectionIndex(): number {
+    return this._selectedConnectionIndex
+  }
+
+  get selectedConnection(): FlowchartActiveEdgeSelection | undefined {
+    const selected = this.selectedOutgoingEdge()
+    return selected ? { from: selected.edge.from, to: selected.edge.to, index: selected.index } : undefined
+  }
+
+  get activeEdge(): FlowchartActiveEdgeSelection | undefined {
+    return this._activeEdge
+  }
+
+  set activeEdge(value: FlowchartActiveEdgeSelection | undefined) {
+    if (flowchartActiveEdgesEqual(this._activeEdge, value)) return
+    this._activeEdge = value ? { ...value } : undefined
+    this.invalidateGrid()
+  }
+
+  set labelColor(value: ColorInput | undefined) {
+    this.setColor(this._labelColor, value, (color) => (this._labelColor = color))
+  }
+
+  set groupColor(value: ColorInput | undefined) {
+    this.setColor(this._groupColor, value, (color) => (this._groupColor = color))
+  }
+
+  activateFirstNode(): string | undefined {
+    if (this._activeNode) return this._activeNode
+    const node = this.parsedDiagram().nodes[0]
+    if (!node) return undefined
+    this.activeNode = node.id
+    return node.id
+  }
+
+  selectNextConnection(): FlowchartActiveEdgeSelection | undefined {
+    return this.selectConnection(1)
+  }
+
+  selectPreviousConnection(): FlowchartActiveEdgeSelection | undefined {
+    return this.selectConnection(-1)
+  }
+
+  private selectConnection(delta: 1 | -1): FlowchartActiveEdgeSelection | undefined {
+    this.activateFirstNode()
+    const outgoing = this.activeOutgoingEdges()
+    if (outgoing.length === 0) return undefined
+    this._activeEdge = undefined
+    if (outgoing.length === 1) {
+      this.invalidateGrid()
+      return this.selectedConnection
+    }
+    this._selectedConnectionIndex = (this._selectedConnectionIndex + delta + outgoing.length) % outgoing.length
+    this.invalidateGrid()
+    return this.selectedConnection
+  }
+
+  followSelectedConnection(): string | undefined {
+    const selected = this.selectedOutgoingEdge()
+    if (!selected) return undefined
+    this._activeNode = selected.edge.to
+    this._activeEdge = undefined
+    this._selectedConnectionIndex = 0
+    this.invalidateGrid()
+    return selected.edge.to
+  }
+
+  private activeOutgoingEdges(): IndexedFlowchartEdge[] {
+    if (!this._activeNode) return []
+    return this.parsedDiagram().edges.flatMap((edge, index) =>
+      edge.from === this._activeNode ? [{ edge, index }] : [],
+    )
+  }
+
+  private selectedOutgoingEdge(): IndexedFlowchartEdge | undefined {
+    const outgoing = this.activeOutgoingEdges()
+    if (outgoing.length === 0) return undefined
+    const index = ((this._selectedConnectionIndex % outgoing.length) + outgoing.length) % outgoing.length
+    return outgoing[index]
+  }
+
+  private renderOptions(): FlowchartDiagramRenderOptions {
+    return {
+      compact: this._compact,
+      direction: this._direction,
+      borderStyle: this._borderStyle,
+      minNodeGap: this._minNodeGap,
+      minRankGap: this._minRankGap,
+      layoutMaxWidth: this._layoutMaxWidth,
+      activeNode: this._activeNode,
+      activeEdge: this._activeEdge ?? this.selectedConnection,
+    }
+  }
+
+  private styledText(grid: FlowchartGrid) {
+    return renderGridStyledText(
+      grid,
+      resolveFlowchartStyleColors({
+        node: this._nodeColor,
+        database: this._databaseColor,
+        edge: this._edgeColor,
+        activeNode: this._activeNodeColor,
+        activeEdge: this._activeEdgeColor,
+        label: this._labelColor,
+        group: this._groupColor,
+      }),
+      this._nodeColors,
+      this._nodeBgColors,
+    )
+  }
+}

packages/merman/src/flowchart/routing.test.ts

@@ -0,0 +1,272 @@
+import { describe, expect, test } from "bun:test"
+import type { FlowchartDiagram, FlowchartNodeBounds } from "./types.js"
+import { routeFlowchartEdges } from "./routing.js"
+
+function bounds(id: string, left: number, top: number): FlowchartNodeBounds {
+  const width = 5
+  const height = 3
+  return {
+    id,
+    width,
+    height,
+    lines: [id],
+    left,
+    top,
+    centerX: left + Math.floor(width / 2),
+    centerY: top + Math.floor(height / 2),
+  }
+}
+
+function diagram(direction: FlowchartDiagram["direction"], edges: FlowchartDiagram["edges"]): FlowchartDiagram {
+  return { direction, nodes: [], edges, subgraphs: [] }
+}
+
+describe("flowchart routing", () => {
+  test("routes a simple horizontal edge from source port to target port", () => {
+    const edge = { from: "A", to: "B", label: "" }
+    const routes = routeFlowchartEdges(
+      diagram("LR", [edge]),
+      new Map([
+        ["A", bounds("A", 0, 0)],
+        ["B", bounds("B", 20, 0)],
+      ]),
+    )
+
+    expect(routes).toEqual([
+      {
+        edge,
+        points: [
+          { x: 5, y: 1 },
+          { x: 19, y: 1 },
+        ],
+      },
+    ])
+  })
+
+  test("routes a simple reverse horizontal edge into the target right port", () => {
+    const edge = { from: "A", to: "B", label: "" }
+    const routes = routeFlowchartEdges(
+      diagram("RL", [edge]),
+      new Map([
+        ["A", bounds("A", 20, 0)],
+        ["B", bounds("B", 0, 0)],
+      ]),
+    )
+
+    expect(routes).toEqual([
+      {
+        edge,
+        points: [
+          { x: 19, y: 1 },
+          { x: 5, y: 1 },
+        ],
+      },
+    ])
+  })
+
+  test("routes horizontal back-edges above forward lanes", () => {
+    const edge = { from: "B", to: "A", label: "" }
+    const routes = routeFlowchartEdges(
+      diagram("LR", [edge]),
+      new Map([
+        ["A", bounds("A", 0, 0)],
+        ["B", bounds("B", 20, 0)],
+      ]),
+    )
+
+    expect(routes).toEqual([
+      {
+        edge,
+        points: [
+          { x: 22, y: -1 },
+          { x: 22, y: -4 },
+          { x: 2, y: -4 },
+          { x: 2, y: -1 },
+        ],
+      },
+    ])
+  })
+
+  test("routes parallel horizontal edges on independent lanes", () => {
+    const edges = [
+      { from: "A", to: "B", label: "first" },
+      { from: "A", to: "B", label: "second" },
+    ]
+    const routes = routeFlowchartEdges(
+      diagram("LR", edges),
+      new Map([
+        ["A", bounds("A", 0, 0)],
+        ["B", bounds("B", 20, 0)],
+      ]),
+    )
+
+    expect(routes.map((route) => route.points)).toEqual([
+      [
+        { x: 5, y: 1 },
+        { x: 19, y: 1 },
+      ],
+      [
+        { x: 2, y: 3 },
+        { x: 2, y: 6 },
+        { x: 22, y: 6 },
+        { x: 22, y: 3 },
+      ],
+    ])
+  })
+
+  test("spaces parallel horizontal lanes for multiline labels", () => {
+    const edges = [
+      { from: "A", to: "B", label: "first" },
+      { from: "A", to: "B", label: "second 1<br/>second 2<br/>second 3" },
+      { from: "A", to: "B", label: "third 1<br/>third 2<br/>third 3" },
+    ]
+    const routes = routeFlowchartEdges(
+      diagram("LR", edges),
+      new Map([
+        ["A", bounds("A", 0, 0)],
+        ["B", bounds("B", 20, 0)],
+      ]),
+    )
+
+    expect(routes[2]!.points[1]!.y).toBeGreaterThan(routes[1]!.points[1]!.y + 3)
+  })
+
+  test("routes horizontal fan-out through a shared bus lane", () => {
+    const edges = [
+      { from: "A", to: "B", label: "" },
+      { from: "A", to: "C", label: "" },
+    ]
+    const routes = routeFlowchartEdges(
+      diagram("LR", edges),
+      new Map([
+        ["A", bounds("A", 0, 6)],
+        ["B", bounds("B", 20, 0)],
+        ["C", bounds("C", 20, 12)],
+      ]),
+    )
+
+    expect(routes.map((route) => route.points)).toEqual([
+      [
+        { x: 5, y: 7 },
+        { x: 8, y: 7 },
+        { x: 8, y: 1 },
+        { x: 19, y: 1 },
+      ],
+      [
+        { x: 5, y: 7 },
+        { x: 8, y: 7 },
+        { x: 8, y: 13 },
+        { x: 19, y: 13 },
+      ],
+    ])
+  })
+
+  test("routes each horizontal edge once when fan-in and fan-out overlap", () => {
+    const edges = [
+      { from: "A", to: "C", label: "" },
+      { from: "A", to: "D", label: "" },
+      { from: "B", to: "C", label: "" },
+      { from: "B", to: "D", label: "" },
+    ]
+    const routes = routeFlowchartEdges(
+      diagram("LR", edges),
+      new Map([
+        ["A", bounds("A", 0, 0)],
+        ["B", bounds("B", 0, 12)],
+        ["C", bounds("C", 24, 0)],
+        ["D", bounds("D", 24, 12)],
+      ]),
+    )
+
+    expect(routes).toHaveLength(edges.length)
+    expect(routes.map((route) => `${route.edge.from}->${route.edge.to}`).sort()).toEqual([
+      "A->C",
+      "A->D",
+      "B->C",
+      "B->D",
+    ])
+  })
+
+  test("routes vertical back-edges around the left side", () => {
+    const edge = { from: "B", to: "A", label: "" }
+    const routes = routeFlowchartEdges(
+      diagram("TD", [edge]),
+      new Map([
+        ["A", bounds("A", 0, 0)],
+        ["B", bounds("B", 0, 12)],
+      ]),
+    )
+
+    expect(routes).toEqual([
+      {
+        edge,
+        points: [
+          { x: -1, y: 13 },
+          { x: -4, y: 13 },
+          { x: -4, y: 1 },
+          { x: -1, y: 1 },
+        ],
+      },
+    ])
+  })
+
+  test("routes self edges below the source node", () => {
+    const edge = { from: "A", to: "A", label: "" }
+    const routes = routeFlowchartEdges(diagram("TD", [edge]), new Map([["A", bounds("A", 0, 0)]]))
+
+    expect(routes).toEqual([
+      {
+        edge,
+        points: [
+          { x: 5, y: 1 },
+          { x: 8, y: 1 },
+          { x: 8, y: 4 },
+          { x: 2, y: 4 },
+          { x: 2, y: 3 },
+        ],
+      },
+    ])
+  })
+
+  test("routes same-column horizontal-flow edges through vertical ports", () => {
+    const edge = { from: "A", to: "B", label: "rollback" }
+    const routes = routeFlowchartEdges(
+      diagram("LR", [edge]),
+      new Map([
+        ["A", bounds("A", 20, 0)],
+        ["B", bounds("B", 20, 8)],
+      ]),
+    )
+
+    expect(routes).toEqual([
+      {
+        edge,
+        points: [
+          { x: 22, y: 3 },
+          { x: 22, y: 7 },
+        ],
+      },
+    ])
+  })
+
+  test("routes overlapping horizontal-flow columns through vertical ports", () => {
+    const edge = { from: "A", to: "B", label: "merge" }
+    const routes = routeFlowchartEdges(
+      diagram("RL", [edge]),
+      new Map([
+        ["A", bounds("A", 1, 8)],
+        ["B", bounds("B", 0, 0)],
+      ]),
+    )
+
+    expect(routes).toEqual([
+      {
+        edge,
+        points: [
+          { x: 2, y: 7 },
+          { x: 2, y: 3 },
+        ],
+      },
+    ])
+  })
+})

packages/merman/src/flowchart/routing.ts

@@ -0,0 +1,703 @@
+import {
+  advanceCoordinate,
+  afterFarthestCoordinate,
+  beforeNearestCoordinate,
+  boundsCenter,
+  boundsSidePoint,
+  centerCoordinate,
+  coordinate,
+  keepAfter,
+  keepBefore,
+  lane,
+  oppositeSide,
+  orthogonalPath,
+  pathThrough,
+  pathViaLane,
+  sideForDirection,
+  snapCoordinate,
+  withCoordinate,
+  type DiagramAxis,
+  type DiagramDirection,
+  type DiagramLane,
+  type DiagramSide,
+} from "../core/geometry.js"
+import { diagramTextWidth, splitDiagramLines } from "../core/text.js"
+import { flowchartEdgeLabelLayout } from "./labels.js"
+import type {
+  FlowchartDiagram,
+  FlowchartDirection,
+  FlowchartEdge,
+  FlowchartEdgeRoute,
+  FlowchartNodeBounds,
+  FlowchartPoint,
+  FlowchartSubgraph,
+  FlowchartSubgraphBounds,
+} from "./types.js"
+
+export { directionBetween as flowchartDirectionBetween } from "../core/geometry.js"
+
+const BUS_CLEARANCE = 3
+const NODE_CLEARANCE = 2
+type HorizontalTravel = Extract<DiagramDirection, "left" | "right">
+type VerticalTravel = Extract<DiagramDirection, "up" | "down">
+type PortRole = "source" | "target"
+
+interface EdgeRecord {
+  edge: FlowchartEdge
+  sourcePort: FlowchartPoint
+  targetPort: FlowchartPoint
+}
+
+function isVerticalDirection(direction: FlowchartDirection): boolean {
+  return direction === "TB" || direction === "TD" || direction === "BT"
+}
+
+function verticalTravel(from: FlowchartNodeBounds, to: FlowchartNodeBounds): VerticalTravel {
+  return centerCoordinate(to, "y") >= centerCoordinate(from, "y") ? "down" : "up"
+}
+
+function isVerticalBackEdge(
+  from: FlowchartNodeBounds,
+  to: FlowchartNodeBounds,
+  direction: FlowchartDirection,
+): boolean {
+  return direction === "BT"
+    ? centerCoordinate(to, "y") > centerCoordinate(from, "y")
+    : centerCoordinate(to, "y") < centerCoordinate(from, "y")
+}
+
+function isHorizontalBackEdge(
+  from: FlowchartNodeBounds,
+  to: FlowchartNodeBounds,
+  direction: FlowchartDirection,
+): boolean {
+  return direction === "RL"
+    ? centerCoordinate(to, "x") > centerCoordinate(from, "x")
+    : centerCoordinate(to, "x") < centerCoordinate(from, "x")
+}
+
+function horizontalTravel(
+  from: FlowchartNodeBounds,
+  to: FlowchartNodeBounds,
+  direction: FlowchartDirection,
+): HorizontalTravel {
+  const targetIsRight = centerCoordinate(to, "x") > centerCoordinate(from, "x")
+  const targetIsSameOrRight = centerCoordinate(to, "x") >= centerCoordinate(from, "x")
+  return direction === "RL" ? (targetIsRight ? "right" : "left") : targetIsSameOrRight ? "right" : "left"
+}
+
+function verticalBackEdgePath(
+  from: FlowchartNodeBounds,
+  to: FlowchartNodeBounds,
+  leftBoundary?: number,
+): FlowchartPoint[] {
+  const start = boundsSidePoint(from, "left")
+  const end = boundsSidePoint(to, "left")
+  const busX = Math.min(
+    afterFarthestCoordinate([start, end], "x", "left", BUS_CLEARANCE),
+    leftBoundary === undefined ? Number.POSITIVE_INFINITY : leftBoundary - BUS_CLEARANCE * 2,
+  )
+  return pathViaLane(start, lane("x", busX), end)
+}
+
+function verticalForwardEdgePath(from: FlowchartNodeBounds, to: FlowchartNodeBounds): FlowchartPoint[] {
+  const travel = verticalTravel(from, to)
+  const startSide = sideForDirection(travel)
+  const endSide = oppositeSide(startSide)
+  const sourceCenter = boundsCenter(from)
+  const targetCenter = boundsCenter(to)
+  const start = withCoordinate(boundsSidePoint(from, startSide), "x", snapCoordinate(sourceCenter.x, targetCenter.x, 1))
+  const end = boundsSidePoint(to, endSide)
+  return orthogonalPath(start, end, { preferredAxis: "y" })
+}
+
+function horizontalBackEdgePath(from: FlowchartNodeBounds, to: FlowchartNodeBounds): FlowchartPoint[] {
+  const start = boundsSidePoint(from, "top")
+  const end = boundsSidePoint(to, "top")
+  const busY = afterFarthestCoordinate([start, end], "y", "up", BUS_CLEARANCE)
+  return pathViaLane(start, lane("y", busY), end)
+}
+
+function horizontalEdgePath(
+  from: FlowchartNodeBounds,
+  to: FlowchartNodeBounds,
+  direction: FlowchartDirection,
+): FlowchartPoint[] {
+  const overlapsHorizontally = from.left < to.left + to.width && to.left < from.left + from.width
+  if (overlapsHorizontally) return verticalForwardEdgePath(from, to)
+
+  if (isHorizontalBackEdge(from, to, direction)) return horizontalBackEdgePath(from, to)
+
+  const travel = horizontalTravel(from, to, direction)
+  const startSide = sideForDirection(travel)
+  return orthogonalPath(boundsSidePoint(from, startSide), boundsSidePoint(to, oppositeSide(startSide)))
+}
+
+function selfEdgePath(bounds: FlowchartNodeBounds): FlowchartPoint[] {
+  const start = boundsSidePoint(bounds, "right")
+  const end = boundsSidePoint(bounds, "bottom")
+  const rightLaneX = bounds.left + bounds.width + BUS_CLEARANCE
+  const bottomLaneY = bounds.top + bounds.height + 1
+  return [start, { x: rightLaneX, y: start.y }, { x: rightLaneX, y: bottomLaneY }, { x: end.x, y: bottomLaneY }, end]
+}
+
+function parallelEdgePath(
+  from: FlowchartNodeBounds,
+  to: FlowchartNodeBounds,
+  direction: FlowchartDirection,
+  laneCoordinate: number,
+): FlowchartPoint[] {
+  if (!isVerticalDirection(direction)) {
+    const start = boundsSidePoint(from, "bottom")
+    const end = boundsSidePoint(to, "bottom")
+    return pathViaLane(start, lane("y", laneCoordinate), end)
+  }
+
+  const start = boundsSidePoint(from, "right")
+  const end = boundsSidePoint(to, "right")
+  return pathViaLane(start, lane("x", laneCoordinate), end)
+}
+
+function labelHeight(edge: FlowchartEdge): number {
+  return edge.label ? splitDiagramLines(edge.label).length : 0
+}
+
+function rightRenderExtent(route: FlowchartEdgeRoute): number {
+  let right = Math.max(...route.points.map((point) => point.x))
+  if (route.edge.label) {
+    const label = flowchartEdgeLabelLayout(route.points, route.edge.label, diagramTextWidth)
+    right = Math.max(right, label.point.x + label.width - 1)
+  }
+  return right
+}
+
+function edgePath(
+  from: FlowchartNodeBounds,
+  to: FlowchartNodeBounds,
+  direction: FlowchartDirection,
+  leftBoundary?: number,
+): FlowchartPoint[] {
+  if (from.id === to.id) return selfEdgePath(from)
+  if (!isVerticalDirection(direction)) return horizontalEdgePath(from, to, direction)
+  return isVerticalBackEdge(from, to, direction)
+    ? verticalBackEdgePath(from, to, leftBoundary)
+    : verticalForwardEdgePath(from, to)
+}
+
+function sourceFanOutLane(
+  sourcePort: FlowchartPoint,
+  targetPorts: readonly FlowchartPoint[],
+  axis: DiagramAxis,
+  travel: DiagramDirection,
+): number {
+  const sourceCoordinate = coordinate(sourcePort, axis)
+  const unclamped = keepBefore(
+    advanceCoordinate(coordinate(sourcePort, axis), travel, BUS_CLEARANCE),
+    beforeNearestCoordinate(targetPorts, axis, travel, NODE_CLEARANCE),
+    travel,
+  )
+  return keepAfter(unclamped, sourceCoordinate, travel)
+}
+
+function targetFanInLane(
+  sourcePorts: readonly FlowchartPoint[],
+  targetPort: FlowchartPoint,
+  axis: DiagramAxis,
+  travel: DiagramDirection,
+): number {
+  const targetCoordinate = coordinate(targetPort, axis)
+  const unclamped = keepAfter(
+    advanceCoordinate(coordinate(targetPort, axis), travel, -BUS_CLEARANCE),
+    afterFarthestCoordinate(sourcePorts, axis, travel, NODE_CLEARANCE),
+    travel,
+  )
+  return keepBefore(unclamped, targetCoordinate, travel)
+}
+
+function portForTravel(bounds: FlowchartNodeBounds, travel: DiagramDirection, role: PortRole): FlowchartPoint {
+  const side = role === "source" ? sideForDirection(travel) : oppositeSide(sideForDirection(travel))
+  return boundsSidePoint(bounds, side)
+}
+
+function horizontalForwardRecords(
+  edges: FlowchartEdge[],
+  bounds: Map<string, FlowchartNodeBounds>,
+  direction: FlowchartDirection,
+): EdgeRecord[] {
+  const travel = direction === "RL" ? "left" : "right"
+  const records: EdgeRecord[] = []
+  for (const edge of edges) {
+    const source = bounds.get(edge.from)
+    const target = bounds.get(edge.to)
+    if (!source || !target) continue
+    const forward =
+      direction === "RL"
+        ? centerCoordinate(target, "x") < centerCoordinate(source, "x")
+        : centerCoordinate(target, "x") > centerCoordinate(source, "x")
+    if (!forward) continue
+    records.push({
+      edge,
+      sourcePort: portForTravel(source, travel, "source"),
+      targetPort: portForTravel(target, travel, "target"),
+    })
+  }
+  return records
+}
+
+function verticalForwardRecords(
+  edges: FlowchartEdge[],
+  bounds: Map<string, FlowchartNodeBounds>,
+  direction: FlowchartDirection,
+): EdgeRecord[] {
+  const travel = direction === "BT" ? "up" : "down"
+  const records: EdgeRecord[] = []
+  for (const edge of edges) {
+    const source = bounds.get(edge.from)
+    const target = bounds.get(edge.to)
+    if (!source || !target) continue
+    const forward =
+      direction === "BT"
+        ? centerCoordinate(target, "y") < centerCoordinate(source, "y")
+        : centerCoordinate(target, "y") > centerCoordinate(source, "y")
+    if (!forward) continue
+    records.push({
+      edge,
+      sourcePort: portForTravel(source, travel, "source"),
+      targetPort: portForTravel(target, travel, "target"),
+    })
+  }
+  return records
+}
+
+function horizontalExitSubgraph(diagram: FlowchartDiagram, edge: FlowchartEdge): FlowchartSubgraph | undefined {
+  for (const subgraph of [...(diagram.subgraphs ?? [])].reverse()) {
+    if (subgraph.direction !== "LR" && subgraph.direction !== "RL") continue
+    if (subgraph.nodeIds.includes(edge.from) && !subgraph.nodeIds.includes(edge.to)) return subgraph
+  }
+  return undefined
+}
+
+function horizontalEntrySubgraph(diagram: FlowchartDiagram, edge: FlowchartEdge): FlowchartSubgraph | undefined {
+  for (const subgraph of [...(diagram.subgraphs ?? [])].reverse()) {
+    if (subgraph.direction !== "LR" && subgraph.direction !== "RL") continue
+    if (subgraph.nodeIds.includes(edge.to) && !subgraph.nodeIds.includes(edge.from)) return subgraph
+  }
+  return undefined
+}
+
+function horizontalSubgraphEntryTravel(subgraph: FlowchartSubgraph): HorizontalTravel {
+  return subgraph.direction === "RL" ? "left" : "right"
+}
+
+function horizontalSubgraphEntryLane(subgraph: FlowchartSubgraph, subgraphBound: FlowchartSubgraphBounds): number {
+  return subgraph.direction === "RL"
+    ? subgraphBound.left + subgraphBound.width + BUS_CLEARANCE
+    : subgraphBound.left - BUS_CLEARANCE
+}
+
+function horizontalSubgraphJoinY(from: FlowchartSubgraphBounds, targetSubgraphBound: FlowchartSubgraphBounds): number {
+  if (from.centerY <= targetSubgraphBound.centerY) {
+    const start = from.top + from.height
+    const end = targetSubgraphBound.top - 1
+    return start <= end ? Math.floor((start + end) / 2) : start
+  }
+
+  const start = targetSubgraphBound.top + targetSubgraphBound.height
+  const end = from.top - 1
+  return start <= end ? Math.floor((start + end) / 2) : end
+}
+
+function horizontalSubgraphExitJoinY(
+  from: FlowchartSubgraphBounds,
+  targetPort: FlowchartPoint,
+  targetBelow: boolean,
+): number {
+  if (targetBelow) {
+    const outside = from.top + from.height
+    const beforeTarget = targetPort.y - 1
+    const preferred = targetPort.y - BUS_CLEARANCE
+    return outside <= beforeTarget ? Math.min(Math.max(outside, preferred), beforeTarget) : beforeTarget
+  }
+
+  const outside = from.top - 1
+  const afterTarget = targetPort.y + 1
+  const preferred = targetPort.y + BUS_CLEARANCE
+  return afterTarget <= outside ? Math.max(Math.min(outside, preferred), afterTarget) : afterTarget
+}
+
+function groupRecords<Record>(records: readonly Record[], key: (record: Record) => string): Map<string, Record[]> {
+  const groups = new Map<string, Record[]>()
+  for (const record of records) {
+    const groupKey = key(record)
+    const group = groups.get(groupKey) ?? []
+    group.push(record)
+    groups.set(groupKey, group)
+  }
+  return groups
+}
+
+function fanRoute(
+  edge: FlowchartEdge,
+  sourcePort: FlowchartPoint,
+  targetPort: FlowchartPoint,
+  routeLane: DiagramLane,
+): FlowchartEdgeRoute {
+  return { edge, points: pathViaLane(sourcePort, routeLane, targetPort) }
+}
+
+function alignClusteredVerticalSources(records: readonly EdgeRecord[]): EdgeRecord[] {
+  const xs = records.map((record) => record.sourcePort.x)
+  const minX = Math.min(...xs)
+  const maxX = Math.max(...xs)
+  if (maxX - minX > 1) return [...records]
+
+  const x = Math.round(xs.reduce((total, value) => total + value, 0) / xs.length)
+  return records.map((record) => ({ ...record, sourcePort: { ...record.sourcePort, x } }))
+}
+
+function routeHorizontalFanOut(
+  records: readonly EdgeRecord[],
+  direction: FlowchartDirection,
+  handled: Set<FlowchartEdge>,
+  routes: FlowchartEdgeRoute[],
+): void {
+  for (const sourceRecords of groupRecords(records, (record) => record.edge.from).values()) {
+    if (sourceRecords.length < 2) continue
+    const travel = direction === "RL" ? "left" : "right"
+    const sourcePort = sourceRecords[0]!.sourcePort
+    const targetPorts = sourceRecords.map((record) => record.targetPort)
+
+    const busX = sourceFanOutLane(sourcePort, targetPorts, "x", travel)
+    for (const record of sourceRecords) {
+      routes.push(fanRoute(record.edge, sourcePort, record.targetPort, lane("x", busX)))
+      handled.add(record.edge)
+    }
+  }
+}
+
+function routeHorizontalFanIn(
+  records: readonly EdgeRecord[],
+  direction: FlowchartDirection,
+  handled: Set<FlowchartEdge>,
+  routes: FlowchartEdgeRoute[],
+): void {
+  const unhandledRecords = records.filter((record) => !handled.has(record.edge))
+  for (const targetRecords of groupRecords(unhandledRecords, (record) => record.edge.to).values()) {
+    if (targetRecords.length < 2) continue
+    const travel = direction === "RL" ? "left" : "right"
+    const targetPort = targetRecords[0]!.targetPort
+    const sourcePorts = targetRecords.map((record) => record.sourcePort)
+
+    const busX = targetFanInLane(sourcePorts, targetPort, "x", travel)
+    for (const record of targetRecords) {
+      routes.push(fanRoute(record.edge, record.sourcePort, targetPort, lane("x", busX)))
+      handled.add(record.edge)
+    }
+  }
+}
+
+function routeVerticalFanOut(
+  records: readonly EdgeRecord[],
+  direction: FlowchartDirection,
+  handled: Set<FlowchartEdge>,
+  routes: FlowchartEdgeRoute[],
+): void {
+  for (const sourceRecords of groupRecords(records, (record) => record.edge.from).values()) {
+    if (sourceRecords.length < 2) continue
+    const travel = direction === "BT" ? "up" : "down"
+    const sourcePort = sourceRecords[0]!.sourcePort
+    const targetPorts = sourceRecords.map((record) => record.targetPort)
+
+    const busY = sourceFanOutLane(sourcePort, targetPorts, "y", travel)
+    for (const record of sourceRecords) {
+      routes.push(fanRoute(record.edge, sourcePort, record.targetPort, lane("y", busY)))
+      handled.add(record.edge)
+    }
+  }
+}
+
+function routeVerticalFanIn(
+  records: readonly EdgeRecord[],
+  direction: FlowchartDirection,
+  handled: Set<FlowchartEdge>,
+  routes: FlowchartEdgeRoute[],
+): void {
+  const unhandledRecords = records.filter((record) => !handled.has(record.edge))
+  for (const unalignedTargetRecords of groupRecords(unhandledRecords, (record) => record.edge.to).values()) {
+    const targetRecords = alignClusteredVerticalSources(unalignedTargetRecords)
+    if (targetRecords.length < 2) continue
+    const travel = direction === "BT" ? "up" : "down"
+    const targetPort = targetRecords[0]!.targetPort
+    const sourcePorts = targetRecords.map((record) => record.sourcePort)
+
+    const busY = targetFanInLane(sourcePorts, targetPort, "y", travel)
+    for (const record of targetRecords) {
+      routes.push(fanRoute(record.edge, record.sourcePort, targetPort, lane("y", busY)))
+      handled.add(record.edge)
+    }
+  }
+}
+
+function routeParallelEdges(
+  diagram: FlowchartDiagram,
+  bounds: Map<string, FlowchartNodeBounds>,
+  directionForEdge: (edge: FlowchartEdge) => FlowchartDirection,
+  leftBoundary: number | undefined,
+  handled: Set<FlowchartEdge>,
+  routes: FlowchartEdgeRoute[],
+): void {
+  const groups = groupRecords(diagram.edges, (edge) => `${directionForEdge(edge)}:${edge.from}:${edge.to}`)
+  for (const edges of groups.values()) {
+    if (edges.length < 2) continue
+    const from = bounds.get(edges[0]!.from)
+    const to = bounds.get(edges[0]!.to)
+    if (!from || !to || from.id === to.id) continue
+    const direction = directionForEdge(edges[0]!)
+    const canonicalRoute = { edge: edges[0]!, points: edgePath(from, to, direction, leftBoundary) }
+    routes.push(canonicalRoute)
+    handled.add(edges[0]!)
+    let previousRoute = canonicalRoute
+    for (let index = 1; index < edges.length; index++) {
+      const edge = edges[index]!
+      const laneCoordinate = isVerticalDirection(direction)
+        ? Math.max(
+            Math.max(boundsSidePoint(from, "right").x, boundsSidePoint(to, "right").x) + BUS_CLEARANCE,
+            rightRenderExtent(previousRoute) + NODE_CLEARANCE,
+          )
+        : Math.max(
+            Math.max(boundsSidePoint(from, "bottom").y, boundsSidePoint(to, "bottom").y) + BUS_CLEARANCE,
+            Math.max(...previousRoute.points.map((point) => point.y)) + Math.max(2, labelHeight(edge) + 1),
+          )
+      const route = { edge, points: parallelEdgePath(from, to, direction, laneCoordinate) }
+      routes.push(route)
+      handled.add(edge)
+      previousRoute = route
+    }
+  }
+}
+
+function routeHorizontalSubgraphExitFanIn(
+  diagram: FlowchartDiagram,
+  bounds: Map<string, FlowchartNodeBounds>,
+  subgraphBounds: ReadonlyMap<string, FlowchartSubgraphBounds> | undefined,
+  handled: Set<FlowchartEdge>,
+  routes: FlowchartEdgeRoute[],
+): void {
+  if (!subgraphBounds) return
+
+  const groups = new Map<string, { edge: FlowchartEdge; subgraph: FlowchartSubgraph; source: FlowchartNodeBounds }[]>()
+  for (const edge of diagram.edges) {
+    if (handled.has(edge)) continue
+    const subgraph = horizontalExitSubgraph(diagram, edge)
+    const source = bounds.get(edge.from)
+    const target = bounds.get(edge.to)
+    if (!subgraph || !source || !target) continue
+
+    const key = `${subgraph.id}:${edge.to}`
+    const group = groups.get(key) ?? []
+    group.push({ edge, subgraph, source })
+    groups.set(key, group)
+  }
+
+  for (const group of groups.values()) {
+    const subgraph = group[0]!.subgraph
+    const subgraphBound = subgraphBounds.get(subgraph.id)
+    const target = bounds.get(group[0]!.edge.to)
+    if (!subgraphBound || !target) continue
+
+    const travel: HorizontalTravel = subgraph.direction === "RL" ? "left" : "right"
+    const busX =
+      subgraph.direction === "RL"
+        ? subgraphBound.left - BUS_CLEARANCE
+        : subgraphBound.left + subgraphBound.width + BUS_CLEARANCE
+    const targetSubgraph = horizontalEntrySubgraph(diagram, group[0]!.edge)
+    const targetSubgraphBound = targetSubgraph ? subgraphBounds.get(targetSubgraph.id) : undefined
+    const targetBelow = target.centerY >= subgraphBound.centerY
+    const targetPort = targetSubgraph
+      ? portForTravel(target, horizontalSubgraphEntryTravel(targetSubgraph), "target")
+      : boundsSidePoint(target, targetBelow ? "top" : "bottom")
+    const joinY = targetSubgraphBound
+      ? horizontalSubgraphJoinY(subgraphBound, targetSubgraphBound)
+      : horizontalSubgraphExitJoinY(subgraphBound, targetPort, targetBelow)
+    const entryX =
+      targetSubgraph && targetSubgraphBound
+        ? horizontalSubgraphEntryLane(targetSubgraph, targetSubgraphBound)
+        : targetPort.x
+
+    for (const record of group) {
+      const sourcePort = portForTravel(record.source, travel, "source")
+      routes.push({
+        edge: record.edge,
+        points: pathThrough([
+          sourcePort,
+          { x: busX, y: sourcePort.y },
+          { x: busX, y: joinY },
+          { x: entryX, y: joinY },
+          { x: entryX, y: targetPort.y },
+          targetPort,
+        ]),
+      })
+      handled.add(record.edge)
+    }
+  }
+}
+
+function routeHorizontalSubgraphEntries(
+  diagram: FlowchartDiagram,
+  bounds: Map<string, FlowchartNodeBounds>,
+  subgraphBounds: ReadonlyMap<string, FlowchartSubgraphBounds> | undefined,
+  handled: Set<FlowchartEdge>,
+  routes: FlowchartEdgeRoute[],
+): void {
+  if (!subgraphBounds) return
+
+  for (const edge of diagram.edges) {
+    if (handled.has(edge)) continue
+    const subgraph = horizontalEntrySubgraph(diagram, edge)
+    const subgraphBound = subgraph ? subgraphBounds.get(subgraph.id) : undefined
+    const from = bounds.get(edge.from)
+    const to = bounds.get(edge.to)
+    if (!subgraph || !subgraphBound || !from || !to) continue
+
+    const targetPort = portForTravel(to, horizontalSubgraphEntryTravel(subgraph), "target")
+    const entryX = horizontalSubgraphEntryLane(subgraph, subgraphBound)
+    const travel = verticalTravel(from, to)
+    const sourcePort = portForTravel(from, travel, "source")
+    routes.push({
+      edge,
+      points: pathThrough([sourcePort, { x: entryX, y: sourcePort.y }, { x: entryX, y: targetPort.y }, targetPort]),
+    })
+    handled.add(edge)
+  }
+}
+
+function pathIntersectsBounds(points: readonly FlowchartPoint[], bounds: FlowchartNodeBounds): boolean {
+  const right = bounds.left + bounds.width - 1
+  const bottom = bounds.top + bounds.height - 1
+  for (let index = 1; index < points.length; index++) {
+    const from = points[index - 1]!
+    const to = points[index]!
+    if (from.x === to.x) {
+      if (
+        from.x >= bounds.left &&
+        from.x <= right &&
+        Math.max(from.y, to.y) >= bounds.top &&
+        Math.min(from.y, to.y) <= bottom
+      ) {
+        return true
+      }
+      continue
+    }
+    if (
+      from.y >= bounds.top &&
+      from.y <= bottom &&
+      Math.max(from.x, to.x) >= bounds.left &&
+      Math.min(from.x, to.x) <= right
+    ) {
+      return true
+    }
+  }
+  return false
+}
+
+function avoidNodeObstacles(
+  route: FlowchartEdgeRoute,
+  bounds: Map<string, FlowchartNodeBounds>,
+  direction: FlowchartDirection,
+): FlowchartEdgeRoute {
+  const obstacle = [...bounds.values()].some(
+    (bound) => bound.id !== route.edge.from && bound.id !== route.edge.to && pathIntersectsBounds(route.points, bound),
+  )
+  if (!obstacle) return route
+
+  const from = bounds.get(route.edge.from)
+  const to = bounds.get(route.edge.to)
+  if (!from || !to) return route
+  if (isVerticalDirection(direction)) {
+    const start = boundsSidePoint(from, "right")
+    const end = boundsSidePoint(to, "right")
+    const busX = Math.max(...[...bounds.values()].map((bound) => bound.left + bound.width - 1)) + BUS_CLEARANCE
+    return { edge: route.edge, points: pathViaLane(start, lane("x", busX), end) }
+  }
+
+  const start = boundsSidePoint(from, "top")
+  const end = boundsSidePoint(to, "top")
+  const busY = Math.min(...[...bounds.values()].map((bound) => bound.top)) - BUS_CLEARANCE
+  return { edge: route.edge, points: pathViaLane(start, lane("y", busY), end) }
+}
+
+export function routeFlowchartEdges(
+  diagram: FlowchartDiagram,
+  bounds: Map<string, FlowchartNodeBounds>,
+  directionForEdge: (edge: FlowchartEdge) => FlowchartDirection = () => diagram.direction,
+  subgraphBounds?: ReadonlyMap<string, FlowchartSubgraphBounds>,
+): FlowchartEdgeRoute[] {
+  const handled = new Set<FlowchartEdge>()
+  const routes: FlowchartEdgeRoute[] = []
+  const leftBoundary = subgraphBounds
+    ? Math.min(...[...bounds.values(), ...subgraphBounds.values()].map((bound) => bound.left))
+    : undefined
+
+  routeParallelEdges(diagram, bounds, directionForEdge, leftBoundary, handled, routes)
+
+  for (const direction of ["LR", "RL"] satisfies FlowchartDirection[]) {
+    const horizontalEdges = diagram.edges.filter((edge) => !handled.has(edge) && directionForEdge(edge) === direction)
+    if (horizontalEdges.length === 0) continue
+    const records = horizontalForwardRecords(horizontalEdges, bounds, direction)
+    routeHorizontalFanOut(records, direction, handled, routes)
+    routeHorizontalFanIn(records, direction, handled, routes)
+  }
+
+  routeHorizontalSubgraphExitFanIn(diagram, bounds, subgraphBounds, handled, routes)
+  routeHorizontalSubgraphEntries(diagram, bounds, subgraphBounds, handled, routes)
+
+  for (const direction of ["TD", "TB", "BT"] satisfies FlowchartDirection[]) {
+    const verticalEdges = diagram.edges.filter((edge) => !handled.has(edge) && directionForEdge(edge) === direction)
+    if (verticalEdges.length === 0) continue
+    const records = verticalForwardRecords(verticalEdges, bounds, direction)
+    routeVerticalFanOut(records, direction, handled, routes)
+    routeVerticalFanIn(records, direction, handled, routes)
+  }
+
+  for (const edge of diagram.edges) {
+    if (handled.has(edge)) continue
+    const from = bounds.get(edge.from)
+    const to = bounds.get(edge.to)
+    if (!from || !to) continue
+    routes.push({ edge, points: edgePath(from, to, directionForEdge(edge), leftBoundary) })
+  }
+  return routes.map((route) => avoidNodeObstacles(route, bounds, directionForEdge(route.edge)))
+}
+
+function sideForOutsidePoint(bounds: FlowchartNodeBounds, sourcePoint: FlowchartPoint): DiagramSide {
+  if (sourcePoint.x < bounds.left) return "left"
+  if (sourcePoint.x >= bounds.left + bounds.width) return "right"
+  if (sourcePoint.y < bounds.top) return "top"
+  return "bottom"
+}
+
+function connectorChar(side: DiagramSide): string {
+  switch (side) {
+    case "left":
+      return "┤"
+    case "right":
+      return "├"
+    case "top":
+      return "┴"
+    case "bottom":
+      return "┬"
+  }
+}
+
+export function flowchartSourceConnector(
+  from: FlowchartNodeBounds,
+  sourcePoint: FlowchartPoint,
+): { x: number; y: number; char: string } {
+  const side = sideForOutsidePoint(from, sourcePoint)
+  const connector = boundsSidePoint(from, side, "border")
+  return {
+    x: side === "top" || side === "bottom" ? sourcePoint.x : connector.x,
+    y: side === "left" || side === "right" ? sourcePoint.y : connector.y,
+    char: connectorChar(side),
+  }
+}

packages/merman/src/flowchart/style.ts

@@ -0,0 +1,109 @@
+import { RGBA, type ColorInput, type StyledText } from "@opentui/core"
+import type { DiagramCanvas, DiagramCanvasRunOptions } from "../core/canvas.js"
+import { diagramCellColorKey, mappedDiagramColor } from "../core/color/map.js"
+import { renderDiagramGridAnsi, renderDiagramGridStyledText } from "../core/render-grid.js"
+import {
+  ansiFg,
+  createColorRampTheme,
+  createAnsiRampTheme,
+  DIAGRAM_FADE_STEPS,
+  numberedStyleKeys,
+  rgba,
+  type DiagramFadeStep,
+  type DiagramRgb,
+} from "../core/color/style.js"
+
+export type FlowchartBaseCellStyle = "node" | "activeNode" | "database" | "edge" | "activeEdge" | "label" | "group"
+export type FlowchartNodeEdgeFadeStyle = `nodeEdgeFade${DiagramFadeStep}`
+export type FlowchartDatabaseEdgeFadeStyle = `databaseEdgeFade${DiagramFadeStep}`
+export type FlowchartEdgeFadeStyle = FlowchartNodeEdgeFadeStyle | FlowchartDatabaseEdgeFadeStyle
+export type FlowchartCellStyle = FlowchartBaseCellStyle | FlowchartEdgeFadeStyle
+export interface FlowchartCellMetadata {
+  nodeId?: string
+  bgNodeId?: string
+}
+export type FlowchartGrid = DiagramCanvas<FlowchartCellStyle, FlowchartCellMetadata>
+export type FlowchartStyleColors = Required<Record<FlowchartCellStyle, RGBA>>
+export type FlowchartDiagramAnsiTheme = Partial<Record<FlowchartCellStyle, string>>
+export type FlowchartNodeColorMap = ReadonlyMap<string, RGBA>
+export type FlowchartNodeColors = Record<string, ColorInput | undefined> | ReadonlyMap<string, ColorInput | undefined>
+
+export function flowchartNodeColorKey(nodeId: string, level: number): string {
+  return diagramCellColorKey(nodeId, level)
+}
+
+export const DEFAULT_THEME_RGB = {
+  node: [228, 239, 232],
+  activeNode: [221, 255, 246],
+  database: [228, 239, 232],
+  edge: [134, 225, 200],
+  activeEdge: [221, 255, 246],
+  label: [134, 225, 200],
+  group: [76, 99, 89],
+} as const satisfies Record<FlowchartBaseCellStyle, DiagramRgb>
+
+export const NODE_EDGE_FADE_STYLES = numberedStyleKeys("nodeEdgeFade", DIAGRAM_FADE_STEPS)
+export const DATABASE_EDGE_FADE_STYLES = numberedStyleKeys("databaseEdgeFade", DIAGRAM_FADE_STEPS)
+
+const DEFAULT_ANSI_THEME: Required<Record<FlowchartCellStyle, string>> = {
+  node: ansiFg(DEFAULT_THEME_RGB.node),
+  activeNode: ansiFg(DEFAULT_THEME_RGB.activeNode),
+  database: ansiFg(DEFAULT_THEME_RGB.database),
+  edge: ansiFg(DEFAULT_THEME_RGB.edge),
+  activeEdge: ansiFg(DEFAULT_THEME_RGB.activeEdge),
+  label: ansiFg(DEFAULT_THEME_RGB.label),
+  group: ansiFg(DEFAULT_THEME_RGB.group),
+  ...createAnsiRampTheme(NODE_EDGE_FADE_STYLES, DEFAULT_THEME_RGB.node, DEFAULT_THEME_RGB.edge),
+  ...createAnsiRampTheme(DATABASE_EDGE_FADE_STYLES, DEFAULT_THEME_RGB.database, DEFAULT_THEME_RGB.edge),
+}
+
+export function resolveFlowchartStyleColors(
+  colors: Partial<Record<FlowchartCellStyle, RGBA | undefined>> = {},
+): FlowchartStyleColors {
+  const node = colors.node ?? rgba(DEFAULT_THEME_RGB.node)
+  const activeNode = colors.activeNode ?? rgba(DEFAULT_THEME_RGB.activeNode)
+  const database = colors.database ?? rgba(DEFAULT_THEME_RGB.database)
+  const edge = colors.edge ?? rgba(DEFAULT_THEME_RGB.edge)
+  const activeEdge = colors.activeEdge ?? rgba(DEFAULT_THEME_RGB.activeEdge)
+  return {
+    node,
+    activeNode,
+    database,
+    edge,
+    activeEdge,
+    label: colors.label ?? rgba(DEFAULT_THEME_RGB.label),
+    group: colors.group ?? rgba(DEFAULT_THEME_RGB.group),
+    ...createColorRampTheme(NODE_EDGE_FADE_STYLES, node, edge),
+    ...createColorRampTheme(DATABASE_EDGE_FADE_STYLES, database, edge),
+  }
+}
+
+function nodeMappedColor(colors: FlowchartNodeColorMap | undefined, nodeId: string | undefined): RGBA | undefined {
+  return mappedDiagramColor(colors, nodeId)
+}
+
+export function renderGridStyledText(
+  grid: FlowchartGrid,
+  colors: FlowchartStyleColors,
+  nodeColors?: FlowchartNodeColorMap,
+  nodeBgColors?: FlowchartNodeColorMap,
+): StyledText {
+  const useNodeRuns = Boolean(nodeColors?.size || nodeBgColors?.size)
+  const runOptions: DiagramCanvasRunOptions<FlowchartCellStyle, FlowchartCellMetadata> = useNodeRuns
+    ? { trimTop: true, trimBottom: true, key: (cell) => [cell.style, cell.nodeId, cell.bgNodeId] }
+    : { trimTop: true, trimBottom: true }
+  return renderDiagramGridStyledText(
+    grid,
+    (run) => nodeMappedColor(nodeColors, run.cell.nodeId) ?? (run.style ? colors[run.style] : undefined),
+    (run) => nodeMappedColor(nodeBgColors, run.cell.bgNodeId),
+    runOptions,
+  )
+}
+
+export function renderGridAnsi(grid: FlowchartGrid, theme: FlowchartDiagramAnsiTheme = {}): string {
+  const resolved = { ...DEFAULT_ANSI_THEME, ...theme }
+  return renderDiagramGridAnsi(grid, (run) => (run.style ? resolved[run.style] : undefined), {
+    trimTop: true,
+    trimBottom: true,
+  })
+}

packages/merman/src/flowchart/types.ts

@@ -0,0 +1,64 @@
+import type { DiagramBounds, DiagramDirection, DiagramPoint } from "../core/geometry.js"
+
+export type FlowchartDirection = "TB" | "TD" | "BT" | "LR" | "RL"
+export type FlowchartNodeShape = "box" | "rounded" | "database" | "decision" | "subroutine"
+export type FlowchartEdgeStyle = "thick" | "dashed"
+
+export interface FlowchartNode {
+  id: string
+  label: string
+  shape: FlowchartNodeShape
+}
+
+export interface FlowchartEdge {
+  from: string
+  to: string
+  label: string
+  style?: FlowchartEdgeStyle
+}
+
+export interface FlowchartSubgraph {
+  id: string
+  label: string
+  nodeIds: string[]
+  parentId?: string
+  direction?: FlowchartDirection
+}
+
+export interface FlowchartDiagram {
+  direction: FlowchartDirection
+  nodes: FlowchartNode[]
+  edges: FlowchartEdge[]
+  subgraphs?: FlowchartSubgraph[]
+}
+
+export interface FlowchartNodeSize {
+  width: number
+  height: number
+  lines: string[]
+}
+
+export interface FlowchartNodeBounds extends FlowchartNodeSize, DiagramBounds {
+  id: string
+}
+
+export interface FlowchartSubgraphBounds extends DiagramBounds {
+  id: string
+  label: string
+  labelSide: "top" | "bottom"
+}
+
+export type FlowchartPoint = DiagramPoint
+
+export interface FlowchartEdgeRoute {
+  edge: FlowchartEdge
+  points: FlowchartPoint[]
+}
+
+export interface FlowchartActiveEdgeSelection {
+  from: string
+  to: string
+  index?: number
+}
+
+export type FlowchartEdgeDirection = DiagramDirection

packages/merman/src/index.ts

@@ -0,0 +1,97 @@
+import * as Flowchart from "./flowchart/index.js"
+import * as Sequence from "./sequence/index.js"
+import * as State from "./state/index.js"
+import { type MermaidDiagramKind } from "./diagnostics.js"
+import { detectMermaidDiagram } from "./detect.js"
+
+export { Flowchart, Sequence, State }
+export { MermaidSyntaxError } from "./diagnostics.js"
+export { createMermaidMarkdownRenderer, type MermaidMarkdownRendererOptions } from "./markdown.js"
+
+export type DiagramKind = MermaidDiagramKind
+
+export type ParsedDiagram =
+  | { readonly kind: "flowchart"; readonly diagram: Flowchart.Diagram }
+  | { readonly kind: "sequence"; readonly diagram: Sequence.Diagram }
+  | { readonly kind: "state"; readonly diagram: State.Diagram }
+
+export interface RenderOptions {
+  /** Emit ANSI color escapes. Default: `true`. Pass `false` for plain text. */
+  color?: boolean
+  /** Theme override. Forwarded to the matching renderer. */
+  theme?: Flowchart.Theme | Sequence.Theme | State.Theme
+}
+
+export class UnknownDiagramError extends Error {
+  readonly _tag = "UnknownDiagramError"
+  constructor(content: string) {
+    const head = firstMeaningfulLine(content) ?? "(empty)"
+    super(
+      `Could not detect diagram kind. Expected the first non-empty line to start with ` +
+        `"flowchart", "graph", "sequenceDiagram", or "stateDiagram[-v2]". Got: "${head}"`,
+    )
+    this.name = "UnknownDiagramError"
+  }
+}
+
+function firstMeaningfulLine(content: string): string | undefined {
+  return content
+    .split(/\r?\n/)
+    .map((line) => line.trim())
+    .find((line) => line.length > 0 && !line.startsWith("%%"))
+}
+
+/**
+ * Detect the diagram kind from the leading Mermaid declaration.
+ *
+ * Returns `undefined` if the content does not look like any supported diagram.
+ */
+export function detect(content: string): DiagramKind | undefined {
+  return detectMermaidDiagram(content)
+}
+
+/** True if the content is recognizably a supported Mermaid diagram. */
+export function isMermaid(content: string): boolean {
+  return detect(content) !== undefined
+}
+
+/**
+ * Render any supported Mermaid string for the terminal.
+ *
+ * The leading `flowchart`/`sequenceDiagram`/`stateDiagram-v2` line picks the
+ * right renderer. Defaults to ANSI-colored output; pass `{ color: false }`
+ * for plain text.
+ *
+ * @throws {UnknownDiagramError} if the diagram kind cannot be detected.
+ */
+export function render(content: string, options: RenderOptions = {}): string {
+  const kind = detect(content)
+  if (!kind) throw new UnknownDiagramError(content)
+  const opts = options as { color?: boolean; theme?: unknown }
+  switch (kind) {
+    case "flowchart":
+      return Flowchart.render(content, opts as Flowchart.RenderOptions)
+    case "sequence":
+      return Sequence.render(content, opts as Sequence.RenderOptions)
+    case "state":
+      return State.render(content, opts as State.RenderOptions)
+  }
+}
+
+/**
+ * Parse any supported Mermaid string into a discriminated union AST.
+ *
+ * @throws {UnknownDiagramError} if the diagram kind cannot be detected.
+ */
+export function parse(content: string): ParsedDiagram {
+  const kind = detect(content)
+  if (!kind) throw new UnknownDiagramError(content)
+  switch (kind) {
+    case "flowchart":
+      return { kind, diagram: Flowchart.parse(content) }
+    case "sequence":
+      return { kind, diagram: Sequence.parse(content) }
+    case "state":
+      return { kind, diagram: State.parse(content) }
+  }
+}

packages/merman/src/markdown.ts

@@ -0,0 +1,131 @@
+import {
+  createMarkdownCodeBlockRenderer,
+  type ColorInput,
+  type MarkdownOptions,
+  type MouseEvent,
+  type RenderContext,
+} from "@opentui/core"
+import { MermaidSyntaxError } from "./diagnostics.js"
+import { detectMermaidDiagram } from "./detect.js"
+import { FlowchartDiagramRenderable } from "./flowchart/renderable.js"
+import { parseMermaidFlowchartDiagram } from "./flowchart/parser.js"
+import { parseMermaidSequenceDiagram } from "./sequence/parser.js"
+import { SequenceDiagramRenderable } from "./sequence/renderable.js"
+import { parseMermaidStateDiagram } from "./state/parser.js"
+import { StateDiagramRenderable } from "./state/renderable.js"
+
+export interface MermaidMarkdownRendererOptions {
+  compact?: boolean
+  colors?: {
+    text?: ColorInput
+    primary?: ColorInput
+    secondary?: ColorInput
+    muted?: ColorInput
+    accent?: ColorInput
+    warning?: ColorInput
+    background?: ColorInput
+  }
+}
+
+/** Create an OpenTUI Markdown node renderer for fenced Mermaid diagrams. */
+export function createMermaidMarkdownRenderer(
+  ctx: RenderContext,
+  input: MermaidMarkdownRendererOptions | (() => MermaidMarkdownRendererOptions) = {},
+): NonNullable<MarkdownOptions["renderNode"]> {
+  return createMarkdownCodeBlockRenderer({
+    mermaid: (token) => {
+      const kind = detectMermaidDiagram(token.text)
+      if (!kind) return undefined
+
+      try {
+        switch (kind) {
+          case "flowchart":
+            parseMermaidFlowchartDiagram(token.text)
+            break
+          case "sequence":
+            parseMermaidSequenceDiagram(token.text)
+            break
+          case "state":
+            parseMermaidStateDiagram(token.text)
+            break
+        }
+        const options = typeof input === "function" ? input() : input
+        const colors = options.colors ?? {}
+        const diagram = (() => {
+          switch (kind) {
+            case "flowchart":
+              return new FlowchartDiagramRenderable(ctx, {
+                content: token.text,
+                compact: options.compact,
+              nodeColor: colors.primary,
+              databaseColor: colors.secondary,
+              edgeColor: colors.secondary,
+              labelColor: colors.text,
+              groupColor: colors.muted,
+              })
+            case "sequence":
+              return new SequenceDiagramRenderable(ctx, {
+                content: token.text,
+                compact: options.compact,
+                participantColor: colors.primary,
+                lifelineColor: colors.muted,
+              groupColor: colors.secondary,
+              requestColor: colors.primary,
+              responseColor: colors.primary,
+                noteColor: colors.warning,
+                noteBackgroundColor: colors.background,
+              })
+            case "state":
+              return new StateDiagramRenderable(ctx, {
+              content: token.text,
+              stateColor: colors.primary,
+              compositeColor: colors.muted,
+              transitionColor: colors.secondary,
+                labelColor: colors.text,
+                noteBorderColor: colors.warning,
+                noteTextColor: colors.warning,
+                noteConnectorColor: colors.muted,
+              activeStateColor: colors.accent,
+              activeTransitionColor: colors.accent,
+              startColor: colors.muted,
+              endColor: colors.muted,
+              choiceColor: colors.primary,
+              })
+          }
+        })()
+        diagram.width = "100%"
+        diagram.height = diagram.renderedHeight
+        diagram.marginTop = 1
+        diagram.selectable = false
+        let drag: { x: number; y: number } | undefined
+        diagram.onMouseDown = (event: MouseEvent) => {
+          if (event.button !== 0) return
+          drag = { x: event.x, y: event.y }
+          event.preventDefault()
+          event.stopPropagation()
+        }
+        diagram.onMouseDrag = (event: MouseEvent) => {
+          if (!drag) return
+          const dx = event.x - drag.x
+          drag = { x: event.x, y: event.y }
+          if (dx) diagram.scrollX -= dx
+          event.preventDefault()
+          event.stopPropagation()
+        }
+        diagram.onMouseDragEnd = () => {
+          drag = undefined
+        }
+        diagram.onMouseUp = (event: MouseEvent) => {
+          if (event.button !== 0) return
+          drag = undefined
+          event.preventDefault()
+          event.stopPropagation()
+        }
+        return diagram
+      } catch (error) {
+        if (error instanceof MermaidSyntaxError) return undefined
+        throw error
+      }
+    },
+  })!
+}

packages/merman/src/plugin.ts

@@ -0,0 +1,23 @@
+import { Plugin } from "@opencode-ai/plugin/tui"
+import { createMermaidMarkdownRenderer } from "./markdown.js"
+
+export default Plugin.define({
+  id: "opencode.merman",
+  setup(context) {
+    context.markdown.registerCodeBlockRenderer(
+      "mermaid",
+      createMermaidMarkdownRenderer(context.renderer, () => ({
+        compact: true,
+        colors: {
+          text: context.theme.markdown.text,
+          primary: context.theme.text.default,
+          secondary: context.theme.text.subdued,
+          muted: context.theme.border.default,
+          accent: context.theme.text.action.primary.focused,
+          warning: context.theme.text.default,
+          background: context.theme.background.default,
+        },
+      })),
+    )
+  },
+})

packages/merman/src/sequence/diagram.test.ts

@@ -0,0 +1,896 @@
+import { describe, expect, test } from "bun:test"
+import { parseColor } from "@opentui/core"
+import { createTestRenderer } from "@opentui/core/testing"
+import { expectDiagram } from "../test/diagram.js"
+import { renderSequenceDiagram, renderSequenceDiagramAnsi } from "./diagram.js"
+import { parseMermaidSequenceDiagram } from "./parser.js"
+import { SequenceDiagramRenderable } from "./renderable.js"
+
+describe("SequenceDiagram", () => {
+  test("parses Mermaid sequenceDiagram participants and messages", () => {
+    const diagram = parseMermaidSequenceDiagram(`
+sequenceDiagram
+  participant B as Browser
+  participant S as Server
+  B->>S: GET /
+  S-->>B: 401 WWW-Auth
+`)
+
+    expect(diagram.participants).toEqual([
+      { id: "B", label: "Browser" },
+      { id: "S", label: "Server" },
+    ])
+    expect(diagram.messages).toEqual([
+      { from: "B", to: "S", label: "GET /", style: "solid" },
+      { from: "S", to: "B", label: "401 WWW-Auth", style: "dashed" },
+    ])
+    expect(diagram.steps).toEqual([
+      { type: "message", message: { from: "B", to: "S", label: "GET /", style: "solid" } },
+      { type: "message", message: { from: "S", to: "B", label: "401 WWW-Auth", style: "dashed" } },
+    ])
+  })
+
+  test("renders a terminal sequence diagram", () => {
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  participant B as Browser
+  participant S as Server
+  B->>S: GET /
+  S-->>B: 401 WWW-Auth
+`)
+
+    expectDiagram(output).toEqualDiagram(`
+      ╭─────────╮       ╭────────╮
+      │ Browser │       │ Server │
+      ╰────┬────╯       ╰────┬───╯
+           │                 │
+           │ GET /           │
+           ├─────────────────▶
+           │                 │
+           │ 401 WWW-Auth    │
+           ◀─────────────────┤
+           │                 │
+    `)
+  })
+
+  test("renders a compact terminal sequence diagram without participant boxes", () => {
+    const output = renderSequenceDiagram(
+      `
+sequenceDiagram
+  participant Leaf as leaf tool
+  participant Location as LocationMutation
+  participant File as FileMutation
+  Leaf->>Location: resolve(path)
+  Location-->>Leaf: Plan(target, authority anchor)
+  Leaf->>File: commit(plan)
+  File->>Location: revalidate(plan)
+  Location-->>File: same target or reject
+`,
+      { compact: true },
+    )
+
+    expectDiagram(output).toEqualDiagram(`
+      leaf tool                       LocationMutation             FileMutation
+          │                                   │                          │
+          ├─ resolve(path) ───────────────────▶                          │
+          │                                   │                          │
+          ◀─ Plan(target, authority anchor) ──┤                          │
+          │                                   │                          │
+          ├─ commit(plan) ───────────────────────────────────────────────▶
+          │                                   │                          │
+          │                                   ◀─ revalidate(plan) ───────┤
+          │                                   │                          │
+          │                                   ├─ same target or reject ──▶
+          │                                   │                          │
+    `)
+  })
+
+  test("keeps structured sequence steps visible in compact mode", () => {
+    const output = renderSequenceDiagram(
+      `
+sequenceDiagram
+  participant Worker
+  participant Store
+  Note over Worker,Store: transaction
+  alt accepted
+    Worker->>Worker: prepare
+    Worker->>Store: commit
+  end
+`,
+      { compact: true },
+    )
+
+    expectDiagram(output).toContainInOrder("Worker", "Store", "transaction", "alt: accepted", "prepare", "commit")
+  })
+
+  test("keeps compact labels above arrows when they do not fit inline", () => {
+    const output = renderSequenceDiagram(
+      "sequenceDiagram\n  participant A\n  participant B\n  participant C\n  A->>C: this label is deliberately much too long to fit between endpoints despite intermediate spacing",
+      { compact: true },
+    )
+    const lines = output.split("\n")
+
+    expect(lines.findIndex((line) => line.includes("deliberately"))).toBeLessThan(
+      lines.findIndex((line) => line.includes("▶")),
+    )
+  })
+
+  test("normalizes invalid participant gaps for text and live rendering", async () => {
+    const content = "sequenceDiagram\n  A->>B: hello"
+
+    expect(renderSequenceDiagram(content, { minParticipantGap: Number.NaN })).toContain("hello")
+
+    const testRenderer = await createTestRenderer({ width: 60, height: 12 })
+    try {
+      const diagram = new SequenceDiagramRenderable(testRenderer.renderer, {
+        content,
+        minParticipantGap: Number.NaN,
+      })
+
+      expect(diagram.minParticipantGap).toBe(18)
+      diagram.minParticipantGap = 0
+      expect(diagram.minParticipantGap).toBe(1)
+      diagram.minParticipantGap = 3.9
+      expect(diagram.minParticipantGap).toBe(3)
+    } finally {
+      testRenderer.renderer.destroy()
+    }
+  })
+
+  test("connects participant headers to lifelines", () => {
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  participant Browser
+  participant Server
+`)
+
+    const lines = output.split("\n")
+    const browserCenter = lines[1]!.indexOf("w")
+    const serverCenter = lines[1]!.indexOf("v")
+
+    expect(lines[2]?.[browserCenter]).toBe("┬")
+    expect(lines[3]?.[browserCenter]).toBe("│")
+    expect(lines[2]?.[serverCenter]).toBe("┬")
+    expect(lines[3]?.[serverCenter]).toBe("│")
+  })
+
+  test("renders notes and long cross-participant messages in order", () => {
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  participant Browser
+  participant Server
+  participant Store as Ticket store
+  Note over Browser,Server: native browser Basic prompt
+  Browser->>Server: POST connect-token
+  Server->>Store: issue { ptyID, scope }
+`)
+
+    expectDiagram(output).toContainInOrder(
+      "native browser Basic prompt",
+      "POST connect-token",
+      "issue { ptyID, scope }",
+    )
+  })
+
+  test("renders notes to the left and right of a participant", () => {
+    const output = renderSequenceDiagram(`sequenceDiagram
+  participant OpenTUI
+  Note right of OpenTUI: child is not renderable
+  Note left of OpenTUI: remove failed`)
+
+    expect(output).toContain("child is not renderable")
+    expect(output).toContain("remove failed")
+  })
+
+  test("preserves the parsed shape of notes over participants", () => {
+    const diagram = parseMermaidSequenceDiagram(`sequenceDiagram
+  participant A
+  Note over A: hello`)
+
+    expect(diagram.steps).toContainEqual({ type: "note", note: { over: ["A"], label: "hello" } })
+  })
+
+  test("parses activation shorthand and control blocks", () => {
+    const diagram = parseMermaidSequenceDiagram(`
+sequenceDiagram
+  Browser->>+Server: request
+  alt accepted
+    Server-->>-Browser: response
+  else rejected
+    activate Server
+    Server-->>Browser: error
+    deactivate Server
+  end
+`)
+
+    expect(diagram.steps).toEqual([
+      {
+        type: "message",
+        message: {
+          from: "Browser",
+          to: "Server",
+          label: "request",
+          style: "solid",
+          activate: "Server",
+        },
+      },
+      { type: "fragment", fragment: { kind: "alt", label: "accepted" } },
+      {
+        type: "message",
+        message: {
+          from: "Server",
+          to: "Browser",
+          label: "response",
+          style: "dashed",
+          deactivate: "Server",
+        },
+      },
+      { type: "fragment", fragment: { kind: "else", label: "rejected" } },
+      { type: "activation", activation: { participant: "Server", active: true } },
+      {
+        type: "message",
+        message: { from: "Server", to: "Browser", label: "error", style: "dashed" },
+      },
+      { type: "activation", activation: { participant: "Server", active: false } },
+      { type: "fragment", fragment: { kind: "end", label: "alt" } },
+    ])
+  })
+
+  test("parses activation syntax without rendering activation bars", () => {
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  Browser->>+Server: request
+  Server-->>-Browser: response
+`)
+
+    expect(output).not.toContain("┃")
+    expect(output).toContain("request")
+    expect(output).toContain("response")
+  })
+
+  test("parses Mermaid arrow head variants", () => {
+    const diagram = parseMermaidSequenceDiagram(`
+sequenceDiagram
+  A->B: open solid
+  B-->A: open dashed
+  A-xB: failed solid
+  B--xA: failed dashed
+  A-)B: async solid
+  B--)A: async dashed
+`)
+
+    expect(diagram.messages).toEqual([
+      { from: "A", to: "B", label: "open solid", style: "solid", head: "open" },
+      { from: "B", to: "A", label: "open dashed", style: "dashed", head: "open" },
+      { from: "A", to: "B", label: "failed solid", style: "solid", head: "cross" },
+      { from: "B", to: "A", label: "failed dashed", style: "dashed", head: "cross" },
+      { from: "A", to: "B", label: "async solid", style: "solid", head: "async" },
+      { from: "B", to: "A", label: "async dashed", style: "dashed", head: "async" },
+    ])
+  })
+
+  test("renders Mermaid arrow head variants", () => {
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  A->B: open solid
+  B-->A: open dashed
+  A-xB: failed solid
+  B--xA: failed dashed
+  A-)B: async solid
+  B--)A: async dashed
+`)
+
+    expect(output).toMatchInlineSnapshot(`
+      "╭───╮              ╭───╮
+      │ A │              │ B │
+      ╰─┬─╯              ╰─┬─╯
+        │                  │
+        │ open solid       │
+        ├─────────────────>│
+        │                  │
+        │ open dashed      │
+        │<─────────────────┤
+        │                  │
+        │ failed solid     │
+        ├─────────────────✕│
+        │                  │
+        │ failed dashed    │
+        │✕─────────────────┤
+        │                  │
+        │ async solid      │
+        ├─────────────────)│
+        │                  │
+        │ async dashed     │
+        │(─────────────────┤
+        │                  │"
+    `)
+  })
+
+  test("renders boxed alt else regions", () => {
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  alt accepted
+    Browser->>Server: ok
+  else rejected
+    Server-->>Browser: no
+  end
+`)
+
+    expectDiagram(output).toContainInOrder("╭─ alt: accepted", "ok", "├─ else: rejected", "no", "╰")
+    expect(output).not.toContain("end alt")
+  })
+
+  test("expands a fragment frame for a longer else label", () => {
+    const output = renderSequenceDiagram(`sequenceDiagram
+  A->>B: start
+  alt ok
+    A->>B: yes
+  else validation failed with a substantially longer explanation
+    B-->>A: no
+  end`)
+    const lines = output.split("\n")
+    const elseRow = lines.find((line) => line.includes("validation failed"))!
+    const endRow = [...lines].reverse().find((line) => line.includes("╰"))!
+
+    expect(elseRow.lastIndexOf("┤")).toBe(endRow.lastIndexOf("╯"))
+  })
+
+  test("preserves combined graphemes in participant names", () => {
+    const output = renderSequenceDiagram(`sequenceDiagram
+  participant A as Cafe\u0301
+  participant B
+  A->>B: hi`)
+
+    expect(output).toContain("Cafe\u0301")
+  })
+
+  test("renders fragment boxes with lifeline overhang", () => {
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  participant A
+  participant B
+  alt ok
+    A->>B: yes
+  end
+`)
+    const lines = output.split("\n")
+    const participantCenter = lines.find((line) => line.includes("│ A │"))!.indexOf("A")
+    const fragmentStart = lines.find((line) => line.includes("alt: ok"))!.indexOf("╭")
+
+    expect(fragmentStart).toBeLessThan(participantCenter)
+  })
+
+  test("supports configurable fragment border styles", () => {
+    const output = renderSequenceDiagram(
+      `
+sequenceDiagram
+  participant A
+  participant B
+  alt ok
+    A->>B: yes
+  else no
+    B-->>A: no
+  end
+`,
+      { fragmentBorderStyle: "double" },
+    )
+
+    expect(output).toContain("╔")
+    expect(output).toContain("╠")
+    expect(output).toContain("╚")
+    expect(output).toContain("═")
+    expect(output).toContain("║")
+  })
+
+  test("parses and renders autonumbered messages", () => {
+    const diagram = parseMermaidSequenceDiagram(`
+sequenceDiagram
+  autonumber
+  Browser->>API: request
+  API-->>Browser: response
+`)
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  autonumber
+  Browser->>API: request
+  API-->>Browser: response
+`)
+
+    expect(diagram.messages.map((message) => message.number)).toEqual([1, 2])
+    expect(output).toContain("1. request")
+    expect(output).toContain("2. response")
+  })
+
+  test("supports autonumber start and increment", () => {
+    const diagram = parseMermaidSequenceDiagram(`
+sequenceDiagram
+  autonumber 10 5
+  Browser->>API: first
+  API-->>Browser: second
+`)
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  autonumber 10 5
+  Browser->>API: first
+  API-->>Browser: second
+`)
+
+    expect(diagram.messages.map((message) => message.number)).toEqual([10, 15])
+    expect(output).toContain("10. first")
+    expect(output).toContain("15. second")
+  })
+
+  test("parses and renders loop regions", () => {
+    const diagram = parseMermaidSequenceDiagram(`
+sequenceDiagram
+  loop retry up to 3x
+    Browser->>API: GET /users/42
+    API-->>Browser: 503
+  end
+`)
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  loop retry up to 3x
+    Browser->>API: GET /users/42
+    API-->>Browser: 503
+  end
+`)
+
+    expect(diagram.steps[0]).toEqual({
+      type: "fragment",
+      fragment: { kind: "loop", label: "retry up to 3x" },
+    })
+    expect(output).toContain("╭─ ↻ loop: retry up to 3x")
+    expect(output).not.toContain("end loop")
+    expect(output.indexOf("loop: retry up to 3x")).toBeLessThan(output.indexOf("GET /users/42"))
+  })
+
+  test("parses Mermaid box participant groups", () => {
+    const diagram = parseMermaidSequenceDiagram(`
+sequenceDiagram
+  participant Browser
+  box Backend
+    participant API
+    participant Cache
+  end
+  box Purple Storage Layer
+    participant DB
+  end
+  box "Purple Literal Label"
+    participant Worker
+  end
+  Browser->>API: request
+`)
+
+    expect(diagram.groups).toEqual([
+      { label: "Backend", participantIds: ["API", "Cache"] },
+      { label: "Storage Layer", participantIds: ["DB"] },
+      { label: "Purple Literal Label", participantIds: ["Worker"] },
+    ])
+    expect(diagram.steps).toEqual([
+      {
+        type: "message",
+        message: { from: "Browser", to: "API", label: "request", style: "solid" },
+      },
+    ])
+  })
+
+  test("adds implicit participants inside box groups", () => {
+    const diagram = parseMermaidSequenceDiagram(`
+sequenceDiagram
+  participant API
+  box Backend
+    API->>DB: query
+  end
+`)
+
+    expect(diagram.groups).toEqual([{ label: "Backend", participantIds: ["API", "DB"] }])
+    expect(diagram.steps).toEqual([
+      { type: "message", message: { from: "API", to: "DB", label: "query", style: "solid" } },
+    ])
+  })
+
+  test("does not clip long non-adjacent messages or notes", () => {
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  participant A
+  participant B
+  participant C
+  A->>C: this message needs room past the final participant
+  Note over A,C: this note also needs full horizontal room
+`)
+
+    expect(output).toContain("this message needs room past the final participant")
+    expect(output).toContain("this note also needs full horizontal room")
+  })
+
+  test("keeps long content inside participant groups and fragment frames", () => {
+    const group = renderSequenceDiagram(`sequenceDiagram
+  box Services
+    participant A
+    participant B
+    participant C
+    A->>C: this message text runs far outside of the group container boundary
+  end`)
+    const fragment = renderSequenceDiagram(`sequenceDiagram
+  participant A
+  participant B
+  participant C
+  alt lookup
+    A->>C: this non adjacent message is deliberately much wider than the frame
+  end`)
+
+    const groupMessageRow = group.split("\n").find((line) => line.includes("this message text"))!
+    const fragmentMessageRow = fragment.split("\n").find((line) => line.includes("this non adjacent message"))!
+    expect(groupMessageRow.trimEnd().endsWith("│")).toBe(true)
+    expect(fragmentMessageRow).toContain("this non adjacent message is deliberately much wider than the frame")
+    expect(fragmentMessageRow.match(/│/g)?.length).toBe(3)
+  })
+
+  test("keeps long notes inside groups and nested fragment frames intact", () => {
+    const groupedNote = renderSequenceDiagram(`sequenceDiagram
+  box Services
+    participant A
+    participant B
+    participant C
+    Note over A,C: this note text runs far outside of the group container boundary
+  end`)
+    const fragmentNote = renderSequenceDiagram(`sequenceDiagram
+  participant A
+  participant B
+  participant C
+  alt lookup
+    Note over A,C: this non adjacent note is deliberately much wider than the frame
+  end`)
+    const nested = renderSequenceDiagram(`sequenceDiagram
+  participant A
+  participant B
+  alt outer
+    loop inner heading wider than outer frame and participant span
+      A->>B: x
+    end
+  end`)
+
+    expect(groupedNote).toContain("this note text runs far outside of the group container boundary")
+    expect(fragmentNote).toContain("this non adjacent note is deliberately much wider than the frame")
+    expect(nested).toContain("span ─╮│")
+    expect(nested).toContain("──────╯│")
+  })
+
+  test("does not draw external participants inside groups expanded by self messages", () => {
+    const output = renderSequenceDiagram(`sequenceDiagram
+  box G
+    participant A
+  end
+  participant B as External
+    A->>A: this self-loop extends underneath the external participant header`)
+    const groupBorderRight = output.split("\n")[0]!.lastIndexOf("╮")
+    const lines = output.split("\n")
+    const externalLabelRow = lines.findIndex((line) => line.includes("External"))
+    const externalHeaderLeft = lines[externalLabelRow - 1]!.lastIndexOf("╭")
+
+    expect(externalHeaderLeft).toBeGreaterThan(groupBorderRight)
+  })
+
+  test("renders full-height participant group boxes", () => {
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  participant Browser
+  box Backend
+    participant API
+    participant Cache
+    participant DB
+  end
+  Browser->>API: GET /users/42
+  API->>Cache: get user:42
+`)
+
+    expect(output).toMatchInlineSnapshot(`
+      "                   ╭─ Backend ──────────────────────────────────╮
+      ╭─────────╮        │ ╭─────╮          ╭───────╮          ╭────╮ │
+      │ Browser │        │ │ API │          │ Cache │          │ DB │ │
+      ╰────┬────╯        │ ╰──┬──╯          ╰───┬───╯          ╰──┬─╯ │
+           │             │    │                 │                 │   │
+           │ GET /users/42    │                 │                 │   │
+           ├──────────────────▶                 │                 │   │
+           │             │    │                 │                 │   │
+           │             │    │ get user:42     │                 │   │
+           │             │    ├─────────────────▶                 │   │
+           │             │    │                 │                 │   │
+                         ╰────────────────────────────────────────────╯"
+    `)
+  })
+
+  test("lets message lines pass through group borders without intersections", () => {
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  participant Browser
+  box Backend
+    participant API
+  end
+  Browser->>API: GET /users/42
+`)
+    const arrowLine = output.split("\n").find((line) => line.includes("▶"))!
+
+    expect(arrowLine).toContain("───────────────▶")
+    expect(arrowLine).not.toContain("┼")
+  })
+
+  test("renders self messages as loopback arrows", () => {
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  participant Service
+  Service->>Service: Check Permissions
+`)
+
+    expect(output).toMatchInlineSnapshot(`
+      "╭─────────╮
+      │ Service │
+      ╰────┬────╯
+           │
+           ├────────────────────╮
+           │ Check Permissions  │
+           ◀────────────────────╯
+           │"
+    `)
+  })
+
+  test("places two spacer rows above note badges and one below", () => {
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  Browser->>Server: one
+  Note over Browser,Server: phase
+  Browser->>Server: two
+`)
+    const lines = output.split("\n")
+    const noteRow = lines.findIndex((line) => line.includes("phase"))
+    const nextMessageRow = lines.findIndex((line) => line.includes("two"))
+
+    expect(noteRow).toBeGreaterThan(0)
+    expect(lines[noteRow - 1]?.trim()).toBe("│                 │")
+    expect(lines[noteRow - 2]?.trim()).toBe("│                 │")
+    expect(lines[noteRow + 1]?.trim()).toBe("│                 │")
+    expect(nextMessageRow).toBe(noteRow + 2)
+  })
+
+  test("renders br-delimited message labels across multiple rows", () => {
+    const output = renderSequenceDiagram(`
+sequenceDiagram
+  Browser->>Server: POST connect-token<br/>· Basic (cached by browser)<br/>· X-OpenCode-Ticket: 1
+`)
+
+    expect(output).toContain("POST connect-token")
+    expect(output).toContain("· Basic (cached by browser)")
+    expect(output).toContain("· X-OpenCode-Ticket: 1")
+    expect(output.indexOf("· X-OpenCode-Ticket: 1")).toBeLessThan(output.indexOf("├"))
+  })
+
+  test("colors request and response messages differently", async () => {
+    const requestColor = parseColor("#38BDF8")
+    const responseColor = parseColor("#F59E0B")
+    const testRenderer = await createTestRenderer({ width: 60, height: 16 })
+
+    try {
+      const diagram = new SequenceDiagramRenderable(testRenderer.renderer, {
+        content: `sequenceDiagram
+  Browser->>Server: request
+  Server-->>Browser: response`,
+        requestColor,
+        responseColor,
+      })
+
+      testRenderer.renderer.root.add(diagram)
+      await testRenderer.renderOnce()
+
+      const spans = testRenderer.captureSpans().lines.flatMap((line) => line.spans)
+      const requestSpan = spans.find((span) => span.text.includes("request"))
+      const responseSpan = spans.find((span) => span.text.includes("response"))
+
+      expect(requestSpan?.fg.equals(requestColor)).toBe(true)
+      expect(responseSpan?.fg.equals(responseColor)).toBe(true)
+    } finally {
+      testRenderer.renderer.destroy()
+    }
+  })
+
+  test("repaints sequence colors after mounting without changing diagram text", async () => {
+    const initialColor = parseColor("#38BDF8")
+    const updatedColor = parseColor("#A78BFA")
+    const testRenderer = await createTestRenderer({ width: 60, height: 12 })
+
+    try {
+      const diagram = new SequenceDiagramRenderable(testRenderer.renderer, {
+        content: "sequenceDiagram\n  Browser->>Server: request",
+        requestColor: initialColor,
+      })
+
+      testRenderer.renderer.root.add(diagram)
+      await testRenderer.renderOnce()
+      const before = testRenderer.captureCharFrame()
+
+      diagram.batchUpdate(() => {
+        diagram.requestColor = updatedColor
+        diagram.lifelineColor = updatedColor
+      })
+      await testRenderer.renderOnce()
+      const spans = testRenderer.captureSpans().lines.flatMap((line) => line.spans)
+
+      expect(testRenderer.captureCharFrame()).toBe(before)
+      expect(spans.find((span) => span.text.includes("request"))?.fg.equals(updatedColor)).toBe(true)
+    } finally {
+      testRenderer.renderer.destroy()
+    }
+  })
+
+  test("tweens arrow departure colors away from lifelines over five cells", async () => {
+    const lifelineColor = parseColor("#94A3B8")
+    const requestColor = parseColor("#38BDF8")
+    const testRenderer = await createTestRenderer({ width: 60, height: 12 })
+
+    try {
+      const diagram = new SequenceDiagramRenderable(testRenderer.renderer, {
+        content: `sequenceDiagram
+  Browser->>Server: request`,
+        lifelineColor,
+        requestColor,
+      })
+
+      testRenderer.renderer.root.add(diagram)
+      await testRenderer.renderOnce()
+
+      const arrowLine = testRenderer
+        .captureSpans()
+        .lines.find((line) => line.spans.some((span) => span.text.includes("▶")))
+      const departureSpan = arrowLine?.spans.find((span) => span.text.includes("├"))
+
+      expect(departureSpan).toBeDefined()
+      expect(departureSpan?.fg.equals(lifelineColor)).toBe(false)
+      expect(departureSpan?.fg.equals(requestColor)).toBe(false)
+    } finally {
+      testRenderer.renderer.destroy()
+    }
+  })
+
+  test("tweens self-message departure colors away from lifelines", async () => {
+    const lifelineColor = parseColor("#94A3B8")
+    const requestColor = parseColor("#38BDF8")
+    const testRenderer = await createTestRenderer({ width: 60, height: 12 })
+
+    try {
+      const diagram = new SequenceDiagramRenderable(testRenderer.renderer, {
+        content: `sequenceDiagram
+  Service->>Service: validate`,
+        lifelineColor,
+        requestColor,
+      })
+
+      testRenderer.renderer.root.add(diagram)
+      await testRenderer.renderOnce()
+
+      const arrowLine = testRenderer
+        .captureSpans()
+        .lines.find((line) => line.spans.some((span) => span.text.includes("├")))
+      const departureSpan = arrowLine?.spans.find((span) => span.text.includes("├"))
+
+      expect(departureSpan).toBeDefined()
+      expect(departureSpan?.fg.equals(lifelineColor)).toBe(false)
+      expect(departureSpan?.fg.equals(requestColor)).toBe(false)
+    } finally {
+      testRenderer.renderer.destroy()
+    }
+  })
+
+  test("colors headers, header rules, and note badges separately", async () => {
+    const participantColor = parseColor("#E5E7EB")
+    const lifelineColor = parseColor("#64748B")
+    const noteColor = parseColor("#A78BFA")
+    const noteBackgroundColor = parseColor("#312E81")
+    const testRenderer = await createTestRenderer({ width: 70, height: 16 })
+
+    try {
+      const diagram = new SequenceDiagramRenderable(testRenderer.renderer, {
+        content: `sequenceDiagram
+  participant Browser
+  participant Server
+  Note over Browser,Server: native browser Basic prompt`,
+        participantColor,
+        lifelineColor,
+        noteColor,
+        noteBackgroundColor,
+      })
+
+      testRenderer.renderer.root.add(diagram)
+      await testRenderer.renderOnce()
+
+      const spans = testRenderer.captureSpans().lines.flatMap((line) => line.spans)
+      const participantSpan = spans.find((span) => span.text.includes("Browser"))
+      const headerRuleSpan = spans.find((span) => span.text.includes("┬"))
+      const noteSpan = spans.find((span) => span.text.includes("native browser Basic prompt"))
+
+      expect(participantSpan?.fg.equals(participantColor)).toBe(true)
+      expect(headerRuleSpan?.fg.equals(lifelineColor)).toBe(true)
+      expect(noteSpan?.fg.equals(noteColor)).toBe(true)
+      expect(noteSpan?.bg.equals(noteBackgroundColor)).toBe(true)
+    } finally {
+      testRenderer.renderer.destroy()
+    }
+  })
+
+  test("colors group boxes separately from fragments", async () => {
+    const groupColor = parseColor("#8BA394")
+    const testRenderer = await createTestRenderer({ width: 70, height: 16 })
+
+    try {
+      const diagram = new SequenceDiagramRenderable(testRenderer.renderer, {
+        content: `sequenceDiagram
+  box Backend
+    participant API
+  end
+  alt ok
+    API->>API: validate
+  end`,
+        groupColor,
+      })
+
+      testRenderer.renderer.root.add(diagram)
+      await testRenderer.renderOnce()
+
+      const spans = testRenderer.captureSpans().lines.flatMap((line) => line.spans)
+      const groupSpan = spans.find((span) => span.text.includes("Backend"))
+      const fragmentSpan = spans.find((span) => span.text.includes("alt: ok"))
+
+      expect(groupSpan?.fg.equals(groupColor)).toBe(true)
+      expect(fragmentSpan?.fg.equals(groupColor)).toBe(false)
+    } finally {
+      testRenderer.renderer.destroy()
+    }
+  })
+
+  test("adds a background to fragment labels", async () => {
+    const noteBackgroundColor = parseColor("#24382F")
+    const testRenderer = await createTestRenderer({ width: 70, height: 16 })
+
+    try {
+      const diagram = new SequenceDiagramRenderable(testRenderer.renderer, {
+        content: `sequenceDiagram
+  alt ok
+    Browser->>Server: request
+  else no
+    Server-->>Browser: response
+  end`,
+        noteBackgroundColor,
+      })
+
+      testRenderer.renderer.root.add(diagram)
+      await testRenderer.renderOnce()
+
+      const spans = testRenderer.captureSpans().lines.flatMap((line) => line.spans)
+      const altSpan = spans.find((span) => span.text.includes("alt: ok"))
+      const elseSpan = spans.find((span) => span.text.includes("else: no"))
+
+      expect(altSpan?.bg.equals(noteBackgroundColor)).toBe(true)
+      expect(elseSpan?.bg.equals(noteBackgroundColor)).toBe(true)
+    } finally {
+      testRenderer.renderer.destroy()
+    }
+  })
+
+  test("prints ANSI colors for terminal dumps", () => {
+    const output = renderSequenceDiagramAnsi(`
+sequenceDiagram
+  Browser->>Server: request
+  Server-->>Browser: response
+`)
+
+    expect(output).toContain("\x1b[38;2;134;225;200m")
+    expect(output).toContain("\x1b[38;2;230;177;126m")
+    expect(output).toContain("\x1b[38;2;115;153;138m")
+    expect(output).toContain("\x1b[38;2;130;211;188m")
+    expect(output).toContain("\x1b[38;2;131;145;126m")
+    expect(output).toContain("\x1b[38;2;210;171;126m")
+    expect(output).toContain("request")
+    expect(output).toContain("response")
+    expect(output).toContain("◀")
+    expect(output).toContain("┤")
+  })
+})

packages/merman/src/sequence/diagram.ts

@@ -0,0 +1,12 @@
+import { drawSequenceDiagramGrid } from "./drawing.js"
+import { parseMermaidSequenceDiagram } from "./parser.js"
+import { renderSequenceGridAnsi, renderSequenceGridText } from "./render-grid.js"
+import type { SequenceDiagramAnsiOptions, SequenceDiagramRenderOptions } from "./types.js"
+
+export function renderSequenceDiagram(content: string, options: SequenceDiagramRenderOptions = {}): string {
+  return renderSequenceGridText(drawSequenceDiagramGrid(parseMermaidSequenceDiagram(content), options))
+}
+
+export function renderSequenceDiagramAnsi(content: string, options: SequenceDiagramAnsiOptions = {}): string {
+  return renderSequenceGridAnsi(drawSequenceDiagramGrid(parseMermaidSequenceDiagram(content), options), options.theme)
+}