refactor(tool): clean up native-friendly parameter schemas

packages/console/app/src/routes/zen/util/handler.ts

@@ -187,6 +187,8 @@ export async function handler(
       // Try another provider => stop retrying if using fallback provider
       if (
         res.status !== 200 &&
+        // ie. 400 error is usually provider error like malformed request
+        res.status !== 400 &&
         // ie. openai 404 error: Item with id 'msg_0ead8b004a3b165d0069436a6b6834819896da85b63b196a3f' not found.
         res.status !== 404 &&
         // ie. cannot change codex model providers mid-session
@@ -226,7 +228,7 @@ export async function handler(
     logger.debug("STATUS: " + res.status + " " + res.statusText)
 
     // Handle non-streaming response
-    if (!isStream || res.status === 429) {
+    if (!isStream || [400, 404, 429].includes(res.status)) {
       const json = await res.json()
       await rateLimiter?.track()
       if (json.usage) {
@@ -238,6 +240,9 @@ export async function handler(
         await reload(billingSource, authInfo, costInfo)
         json.cost = calculateOccurredCost(billingSource, costInfo)
       }
+      if (res.status === 400) {
+        logger.metric({ "error.response": JSON.stringify(json) })
+      }
       if (json.error?.message) {
         json.error.message = `Error from provider${providerInfo.displayName ? ` (${providerInfo.displayName})` : ""}: ${json.error.message}`
       }
@@ -393,7 +398,7 @@ export async function handler(
         type: "error",
         error: {
           type: "error",
-          message: error.message,
+          message: "Internal server error",
         },
       }),
       { status: 500 },

packages/opencode/specs/effect/schema.md

@@ -147,6 +147,17 @@ import `z` do so only for local `ZodOverride` bridges or for `z.ZodType`
 type annotations — the `export const <Info|Spec>` values are all Effect
 Schema at source.
 
+A file is considered "done" when:
+
+- its exported schema values (`Info`, `Input`, `Event`, `Definition`, etc.)
+  are authored as Effect Schema
+- any remaining zod is either a derived compat bridge (via `zod()` /
+  `zodObject()`), a `z.ZodType` type annotation, or a documented
+  `ZodOverride` escape hatch — never a hand-written parallel source of truth
+
+Files that meet this bar but still carry a compat bridge are checked off
+with an inline note describing the bridge and what unblocks its removal.
+
 - [x] skills, formatter, console-state, mcp, lsp, permission (leaves), model-id, command, plugin, provider
 - [x] server, layout
 - [x] keybinds
@@ -263,9 +274,9 @@ Possible later tightening after the Schema-first migration is stable:
 
 ### Provider domain
 
-- [ ] `src/provider/auth.ts`
-- [ ] `src/provider/models.ts`
-- [ ] `src/provider/provider.ts`
+- [x] `src/provider/auth.ts`
+- [x] `src/provider/models.ts`
+- [x] `src/provider/provider.ts`
 
 ### Tool schemas
 
@@ -365,7 +376,7 @@ piecewise.
 - [ ] `src/snapshot/index.ts`
 - [ ] `src/storage/db.ts`
 - [ ] `src/storage/storage.ts`
-- [ ] `src/sync/index.ts`
+- [x] `src/sync/index.ts` — public API (`SyncEvent.define`) is Schema-first; still stores derived zod `schema`/`properties` on each `Definition` as a compat bridge for `BusEvent` until `bus/bus-event.ts` migrates
 - [ ] `src/util/fn.ts`
 - [ ] `src/util/log.ts`
 - [ ] `src/util/update-schema.ts`

packages/opencode/src/bus/bus-event.ts

@@ -1,15 +1,19 @@
 import z from "zod"
-import type { ZodType } from "zod"
+import { Schema } from "effect"
+import { zodObject } from "@/util/effect-zod"
 
-export type Definition = ReturnType<typeof define>
+export type Definition<Type extends string = string, Properties extends Schema.Top = Schema.Top> = {
+  type: Type
+  properties: Properties
+}
 
 const registry = new Map<string, Definition>()
 
-export function define<Type extends string, Properties extends ZodType>(type: Type, properties: Properties) {
-  const result = {
-    type,
-    properties,
-  }
+export function define<Type extends string, Properties extends Schema.Top>(
+  type: Type,
+  properties: Properties,
+): Definition<Type, Properties> {
+  const result = { type, properties }
   registry.set(type, result)
   return result
 }
@@ -21,7 +25,7 @@ export function payloads() {
       return z
         .object({
           type: z.literal(type),
-          properties: def.properties,
+          properties: zodObject(def.properties),
         })
         .meta({
           ref: `Event.${def.type}`,

packages/opencode/src/bus/index.ts

@@ -1,5 +1,4 @@
-import z from "zod"
-import { Effect, Exit, Layer, PubSub, Scope, Context, Stream } from "effect"
+import { Effect, Exit, Layer, PubSub, Scope, Context, Stream, Schema } from "effect"
 import { EffectBridge } from "@/effect"
 import { Log } from "../util"
 import { BusEvent } from "./bus-event"
@@ -9,16 +8,18 @@ import { makeRuntime } from "@/effect/run-service"
 
 const log = Log.create({ service: "bus" })
 
+type BusProperties<D extends BusEvent.Definition<string, Schema.Top>> = Schema.Schema.Type<D["properties"]>
+
 export const InstanceDisposed = BusEvent.define(
   "server.instance.disposed",
-  z.object({
-    directory: z.string(),
+  Schema.Struct({
+    directory: Schema.String,
   }),
 )
 
 type Payload<D extends BusEvent.Definition = BusEvent.Definition> = {
   type: D["type"]
-  properties: z.infer<D["properties"]>
+  properties: BusProperties<D>
 }
 
 type State = {
@@ -27,10 +28,7 @@ type State = {
 }
 
 export interface Interface {
-  readonly publish: <D extends BusEvent.Definition>(
-    def: D,
-    properties: z.output<D["properties"]>,
-  ) => Effect.Effect<void>
+  readonly publish: <D extends BusEvent.Definition>(def: D, properties: BusProperties<D>) => Effect.Effect<void>
   readonly subscribe: <D extends BusEvent.Definition>(def: D) => Stream.Stream<Payload<D>>
   readonly subscribeAll: () => Stream.Stream<Payload>
   readonly subscribeCallback: <D extends BusEvent.Definition>(
@@ -79,7 +77,7 @@ export const layer = Layer.effect(
       })
     }
 
-    function publish<D extends BusEvent.Definition>(def: D, properties: z.output<D["properties"]>) {
+    function publish<D extends BusEvent.Definition>(def: D, properties: BusProperties<D>) {
       return Effect.gen(function* () {
         const s = yield* InstanceState.get(state)
         const payload: Payload = { type: def.type, properties }
@@ -175,14 +173,11 @@ const { runPromise, runSync } = makeRuntime(Service, layer)
 
 // runSync is safe here because the subscribe chain (InstanceState.get, PubSub.subscribe,
 // Scope.make, Effect.forkScoped) is entirely synchronous. If any step becomes async, this will throw.
-export async function publish<D extends BusEvent.Definition>(def: D, properties: z.output<D["properties"]>) {
+export async function publish<D extends BusEvent.Definition>(def: D, properties: BusProperties<D>) {
   return runPromise((svc) => svc.publish(def, properties))
 }
 
-export function subscribe<D extends BusEvent.Definition>(
-  def: D,
-  callback: (event: { type: D["type"]; properties: z.infer<D["properties"]> }) => unknown,
-) {
+export function subscribe<D extends BusEvent.Definition>(def: D, callback: (event: Payload<D>) => unknown) {
   return runSync((svc) => svc.subscribeCallback(def, callback))
 }
 

packages/opencode/src/cli/cmd/tui/event.ts

@@ -1,14 +1,14 @@
 import { BusEvent } from "@/bus/bus-event"
 import { SessionID } from "@/session/schema"
-import z from "zod"
+import { Schema } from "effect"
 
 export const TuiEvent = {
-  PromptAppend: BusEvent.define("tui.prompt.append", z.object({ text: z.string() })),
+  PromptAppend: BusEvent.define("tui.prompt.append", Schema.Struct({ text: Schema.String })),
   CommandExecute: BusEvent.define(
     "tui.command.execute",
-    z.object({
-      command: z.union([
-        z.enum([
+    Schema.Struct({
+      command: Schema.Union([
+        Schema.Literals([
           "session.list",
           "session.new",
           "session.share",
@@ -26,23 +26,23 @@ export const TuiEvent = {
           "prompt.submit",
           "agent.cycle",
         ]),
-        z.string(),
+        Schema.String,
       ]),
     }),
   ),
   ToastShow: BusEvent.define(
     "tui.toast.show",
-    z.object({
-      title: z.string().optional(),
-      message: z.string(),
-      variant: z.enum(["info", "success", "warning", "error"]),
-      duration: z.number().default(5000).optional().describe("Duration in milliseconds"),
+    Schema.Struct({
+      title: Schema.optional(Schema.String),
+      message: Schema.String,
+      variant: Schema.Literals(["info", "success", "warning", "error"]),
+      duration: Schema.optional(Schema.Number).annotate({ description: "Duration in milliseconds" }),
     }),
   ),
   SessionSelect: BusEvent.define(
     "tui.session.select",
-    z.object({
-      sessionID: SessionID.zod.describe("Session ID to navigate to"),
+    Schema.Struct({
+      sessionID: SessionID.annotate({ description: "Session ID to navigate to" }),
     }),
   ),
 }

packages/opencode/src/cli/cmd/tui/ui/toast.tsx

@@ -4,10 +4,10 @@ import { useTheme } from "@tui/context/theme"
 import { useTerminalDimensions } from "@opentui/solid"
 import { SplitBorder } from "../component/border"
 import { TextAttributes } from "@opentui/core"
-import z from "zod"
+import { Schema } from "effect"
 import { type TuiEvent } from "../event"
 
-export type ToastOptions = z.infer<typeof TuiEvent.ToastShow.properties>
+export type ToastOptions = Schema.Schema.Type<typeof TuiEvent.ToastShow.properties>
 
 export function Toast() {
   const toast = useToast()

packages/opencode/src/command/index.ts

@@ -3,7 +3,7 @@ import { InstanceState } from "@/effect"
 import { EffectBridge } from "@/effect"
 import type { InstanceContext } from "@/project/instance"
 import { SessionID, MessageID } from "@/session/schema"
-import { Effect, Layer, Context } from "effect"
+import { Effect, Layer, Context, Schema } from "effect"
 import z from "zod"
 import { Config } from "../config"
 import { MCP } from "../mcp"
@@ -18,11 +18,11 @@ type State = {
 export const Event = {
   Executed: BusEvent.define(
     "command.executed",
-    z.object({
-      name: z.string(),
-      sessionID: SessionID.zod,
-      arguments: z.string(),
-      messageID: MessageID.zod,
+    Schema.Struct({
+      name: Schema.String,
+      sessionID: SessionID,
+      arguments: Schema.String,
+      messageID: MessageID,
     }),
   ),
 }

packages/opencode/src/config/agent.ts

@@ -4,6 +4,7 @@ import { Schema } from "effect"
 import z from "zod"
 import { Bus } from "@/bus"
 import { zod } from "@/util/effect-zod"
+import { PositiveInt } from "@/util/schema"
 import { Log } from "../util"
 import { NamedError } from "@opencode-ai/shared/util/error"
 import { Glob } from "@opencode-ai/shared/util/glob"
@@ -15,8 +16,6 @@ import { ConfigPermission } from "./permission"
 
 const log = Log.create({ service: "config" })
 
-const PositiveInt = Schema.Number.check(Schema.isInt()).check(Schema.isGreaterThan(0))
-
 const Color = Schema.Union([
   Schema.String.check(Schema.isPattern(/^#[0-9a-fA-F]{6}$/)),
   Schema.Literals(["primary", "secondary", "accent", "success", "warning", "error", "info"]),

packages/opencode/src/config/config.ts

@@ -25,7 +25,7 @@ import { Context, Duration, Effect, Exit, Fiber, Layer, Option, Schema } from "e
 import { EffectFlock } from "@opencode-ai/shared/util/effect-flock"
 import { InstanceRef } from "@/effect/instance-ref"
 import { zod, ZodOverride } from "@/util/effect-zod"
-import { withStatics } from "@/util/schema"
+import { NonNegativeInt, PositiveInt, withStatics, type DeepMutable } from "@/util/schema"
 import { ConfigAgent } from "./agent"
 import { ConfigCommand } from "./command"
 import { ConfigFormatter } from "./formatter"
@@ -88,9 +88,6 @@ export type Layout = ConfigLayout.Layout
 const AgentRef = Schema.Any.annotate({ [ZodOverride]: ConfigAgent.Info })
 const LogLevelRef = Schema.Any.annotate({ [ZodOverride]: Log.Level })
 
-const PositiveInt = Schema.Number.check(Schema.isInt()).check(Schema.isGreaterThan(0))
-const NonNegativeInt = Schema.Number.check(Schema.isInt()).check(Schema.isGreaterThanOrEqualTo(0))
-
 // The Effect Schema is the canonical source of truth. The `.zod` compatibility
 // surface is derived so existing Hono validators keep working without a parallel
 // Zod definition.
@@ -252,26 +249,9 @@ export const Info = Schema.Struct({
     })),
   )
 
-// Schema.Struct produces readonly types by default, but the service code
-// below mutates Info objects directly (e.g. `config.mode = ...`). Strip the
-// readonly recursively so callers get the same mutable shape zod inferred.
-//
-// `Types.DeepMutable` from effect-smol would be a drop-in, but its fallback
-// branch `{ -readonly [K in keyof T]: ... }` collapses `unknown` to `{}`
-// (since `keyof unknown = never`), which widens `Record<string, unknown>`
-// fields like `ConfigPlugin.Options`. The local version gates on
-// `extends object` so `unknown` passes through.
-//
-// Tuple branch preserves `ConfigPlugin.Spec`'s `readonly [string, Options]`
-// shape (otherwise the general array branch widens it to an array).
-type DeepMutable<T> = T extends readonly [unknown, ...unknown[]]
-  ? { -readonly [K in keyof T]: DeepMutable<T[K]> }
-  : T extends readonly (infer U)[]
-    ? DeepMutable<U>[]
-    : T extends object
-      ? { -readonly [K in keyof T]: DeepMutable<T[K]> }
-      : T
-
+// Uses the shared `DeepMutable` from `@/util/schema`. See the definition
+// there for why the local variant is needed over `Types.DeepMutable` from
+// effect-smol (the upstream version collapses `unknown` to `{}`).
 export type Info = DeepMutable<Schema.Schema.Type<typeof Info>> & {
   // plugin_origins is derived state, not a persisted config field. It keeps each winning plugin spec together
   // with the file and scope it came from so later runtime code can make location-sensitive decisions.

packages/opencode/src/config/provider.ts

@@ -1,8 +1,6 @@
 import { Schema } from "effect"
 import { zod } from "@/util/effect-zod"
-import { withStatics } from "@/util/schema"
-
-const PositiveInt = Schema.Number.check(Schema.isInt()).check(Schema.isGreaterThan(0))
+import { PositiveInt, withStatics } from "@/util/schema"
 
 export const Model = Schema.Struct({
   id: Schema.optional(Schema.String),

packages/opencode/src/config/server.ts

@@ -1,9 +1,9 @@
 import { Schema } from "effect"
 import { zod } from "@/util/effect-zod"
-import { withStatics } from "@/util/schema"
+import { PositiveInt, withStatics } from "@/util/schema"
 
 export const Server = Schema.Struct({
-  port: Schema.optional(Schema.Number.check(Schema.isInt()).check(Schema.isGreaterThan(0))).annotate({
+  port: Schema.optional(PositiveInt).annotate({
     description: "Port to listen on",
   }),
   hostname: Schema.optional(Schema.String).annotate({ description: "Hostname to listen on" }),

packages/opencode/src/control-plane/workspace.ts

@@ -1,4 +1,5 @@
 import z from "zod"
+import { Schema } from "effect"
 import { setTimeout as sleep } from "node:timers/promises"
 import { fn } from "@/util/fn"
 import { Database, asc, eq, inArray } from "@/storage"
@@ -25,36 +26,37 @@ import { errorData } from "@/util/error"
 import { AppRuntime } from "@/effect/app-runtime"
 import { waitEvent } from "./util"
 import { WorkspaceContext } from "./workspace-context"
+import { NonNegativeInt } from "@/util/schema"
 
 export const Info = WorkspaceInfo.meta({
   ref: "Workspace",
 })
 export type Info = z.infer<typeof Info>
 
-export const ConnectionStatus = z.object({
-  workspaceID: WorkspaceID.zod,
-  status: z.enum(["connected", "connecting", "disconnected", "error"]),
+export const ConnectionStatus = Schema.Struct({
+  workspaceID: WorkspaceID,
+  status: Schema.Literals(["connected", "connecting", "disconnected", "error"]),
 })
-export type ConnectionStatus = z.infer<typeof ConnectionStatus>
+export type ConnectionStatus = Schema.Schema.Type<typeof ConnectionStatus>
 
-const Restore = z.object({
-  workspaceID: WorkspaceID.zod,
-  sessionID: SessionID.zod,
-  total: z.number().int().min(0),
-  step: z.number().int().min(0),
+const Restore = Schema.Struct({
+  workspaceID: WorkspaceID,
+  sessionID: SessionID,
+  total: NonNegativeInt,
+  step: NonNegativeInt,
 })
 
 export const Event = {
   Ready: BusEvent.define(
     "workspace.ready",
-    z.object({
-      name: z.string(),
+    Schema.Struct({
+      name: Schema.String,
     }),
   ),
   Failed: BusEvent.define(
     "workspace.failed",
-    z.object({
-      message: z.string(),
+    Schema.Struct({
+      message: Schema.String,
     }),
   ),
   Restore: BusEvent.define("workspace.restore", Restore),

packages/opencode/src/file/index.ts

@@ -3,7 +3,7 @@ import { InstanceState } from "@/effect"
 
 import { AppFileSystem } from "@opencode-ai/shared/filesystem"
 import { Git } from "@/git"
-import { Effect, Layer, Context, Scope } from "effect"
+import { Effect, Layer, Context, Schema, Scope } from "effect"
 import * as Stream from "effect/Stream"
 import { formatPatch, structuredPatch } from "diff"
 import fuzzysort from "fuzzysort"
@@ -76,8 +76,8 @@ export type Content = z.infer<typeof Content>
 export const Event = {
   Edited: BusEvent.define(
     "file.edited",
-    z.object({
-      file: z.string(),
+    Schema.Struct({
+      file: Schema.String,
     }),
   ),
 }

packages/opencode/src/file/watcher.ts

@@ -1,4 +1,4 @@
-import { Cause, Effect, Layer, Context } from "effect"
+import { Cause, Effect, Layer, Context, Schema } from "effect"
 // @ts-ignore
 import { createWrapper } from "@parcel/watcher/wrapper"
 import type ParcelWatcher from "@parcel/watcher"
@@ -25,9 +25,9 @@ const SUBSCRIBE_TIMEOUT_MS = 10_000
 export const Event = {
   Updated: BusEvent.define(
     "file.watcher.updated",
-    z.object({
-      file: z.string(),
-      event: z.union([z.literal("add"), z.literal("change"), z.literal("unlink")]),
+    Schema.Struct({
+      file: Schema.String,
+      event: Schema.Literals(["add", "change", "unlink"]),
     }),
   ),
 }

packages/opencode/src/ide/index.ts

@@ -1,5 +1,6 @@
 import { BusEvent } from "@/bus/bus-event"
 import z from "zod"
+import { Schema } from "effect"
 import { NamedError } from "@opencode-ai/shared/util/error"
 import { Log } from "../util"
 import { Process } from "@/util"
@@ -17,8 +18,8 @@ const log = Log.create({ service: "ide" })
 export const Event = {
   Installed: BusEvent.define(
     "ide.installed",
-    z.object({
-      ide: z.string(),
+    Schema.Struct({
+      ide: Schema.String,
     }),
   ),
 }

packages/opencode/src/installation/index.ts

@@ -21,14 +21,14 @@ export type ReleaseType = "patch" | "minor" | "major"
 export const Event = {
   Updated: BusEvent.define(
     "installation.updated",
-    z.object({
-      version: z.string(),
+    Schema.Struct({
+      version: Schema.String,
     }),
   ),
   UpdateAvailable: BusEvent.define(
     "installation.update-available",
-    z.object({
-      version: z.string(),
+    Schema.Struct({
+      version: Schema.String,
     }),
   ),
 }

packages/opencode/src/lsp/client.ts

@@ -8,6 +8,7 @@ import { Log } from "../util"
 import { Process } from "../util"
 import { LANGUAGE_EXTENSIONS } from "./language"
 import z from "zod"
+import { Schema } from "effect"
 import type * as LSPServer from "./server"
 import { NamedError } from "@opencode-ai/shared/util/error"
 import { withTimeout } from "../util/timeout"
@@ -41,9 +42,9 @@ export const InitializeError = NamedError.create(
 export const Event = {
   Diagnostics: BusEvent.define(
     "lsp.client.diagnostics",
-    z.object({
-      serverID: z.string(),
-      path: z.string(),
+    Schema.Struct({
+      serverID: Schema.String,
+      path: Schema.String,
     }),
   ),
 }

packages/opencode/src/lsp/lsp.ts

@@ -19,7 +19,7 @@ import { zod, ZodOverride } from "@/util/effect-zod"
 const log = Log.create({ service: "lsp" })
 
 export const Event = {
-  Updated: BusEvent.define("lsp.updated", z.object({})),
+  Updated: BusEvent.define("lsp.updated", Schema.Struct({})),
 }
 
 const Position = Schema.Struct({

packages/opencode/src/mcp/index.ts

@@ -25,7 +25,7 @@ import { BusEvent } from "../bus/bus-event"
 import { Bus } from "@/bus"
 import { TuiEvent } from "@/cli/cmd/tui/event"
 import open from "open"
-import { Effect, Exit, Layer, Option, Context, Stream } from "effect"
+import { Effect, Exit, Layer, Option, Context, Schema, Stream } from "effect"
 import { EffectBridge } from "@/effect"
 import { InstanceState } from "@/effect"
 import { ChildProcess, ChildProcessSpawner } from "effect/unstable/process"
@@ -47,16 +47,16 @@ export type Resource = z.infer<typeof Resource>
 
 export const ToolsChanged = BusEvent.define(
   "mcp.tools.changed",
-  z.object({
-    server: z.string(),
+  Schema.Struct({
+    server: Schema.String,
   }),
 )
 
 export const BrowserOpenFailed = BusEvent.define(
   "mcp.browser.open.failed",
-  z.object({
-    mcpName: z.string(),
-    url: z.string(),
+  Schema.Struct({
+    mcpName: Schema.String,
+    url: Schema.String,
   }),
 )
 

packages/opencode/src/permission/index.ts

@@ -73,16 +73,14 @@ export class Approval extends Schema.Class<Approval>("PermissionApproval")({
 }
 
 export const Event = {
-  Asked: BusEvent.define("permission.asked", Request.zod),
+  Asked: BusEvent.define("permission.asked", Request),
   Replied: BusEvent.define(
     "permission.replied",
-    zod(
-      Schema.Struct({
-        sessionID: SessionID,
-        requestID: PermissionID,
-        reply: Reply,
-      }),
-    ),
+    Schema.Struct({
+      sessionID: SessionID,
+      requestID: PermissionID,
+      reply: Reply,
+    }),
   ),
 }
 

packages/opencode/src/project/project.ts

@@ -53,7 +53,7 @@ export const Info = Schema.Struct({
 export type Info = Types.DeepMutable<Schema.Schema.Type<typeof Info>>
 
 export const Event = {
-  Updated: BusEvent.define("project.updated", Info.zod),
+  Updated: BusEvent.define("project.updated", Info),
 }
 
 type Row = typeof ProjectTable.$inferSelect

packages/opencode/src/project/vcs.ts

@@ -1,4 +1,4 @@
-import { Effect, Layer, Context, Stream, Scope } from "effect"
+import { Effect, Layer, Context, Schema, Stream, Scope } from "effect"
 import { formatPatch, structuredPatch } from "diff"
 import path from "path"
 import { Bus } from "@/bus"
@@ -107,8 +107,8 @@ export type Mode = z.infer<typeof Mode>
 export const Event = {
   BranchUpdated: BusEvent.define(
     "vcs.branch.updated",
-    z.object({
-      branch: z.string().optional(),
+    Schema.Struct({
+      branch: Schema.optional(Schema.String),
     }),
   ),
 }

packages/opencode/src/provider/auth.ts

@@ -1,13 +1,12 @@
 import type { AuthOAuthResult, Hooks } from "@opencode-ai/plugin"
-import { NamedError } from "@opencode-ai/shared/util/error"
 import { Auth } from "@/auth"
 import { InstanceState } from "@/effect"
 import { zod } from "@/util/effect-zod"
+import { namedSchemaError } from "@/util/named-schema-error"
 import { withStatics } from "@/util/schema"
 import { Plugin } from "../plugin"
 import { ProviderID } from "./schema"
 import { Array as Arr, Effect, Layer, Record, Result, Context, Schema } from "effect"
-import z from "zod"
 
 const When = Schema.Struct({
   key: Schema.String,
@@ -70,22 +69,16 @@ export const CallbackInput = Schema.Struct({
 }).pipe(withStatics((s) => ({ zod: zod(s) })))
 export type CallbackInput = Schema.Schema.Type<typeof CallbackInput>
 
-export const OauthMissing = NamedError.create("ProviderAuthOauthMissing", z.object({ providerID: ProviderID.zod }))
+export const OauthMissing = namedSchemaError("ProviderAuthOauthMissing", { providerID: ProviderID })
 
-export const OauthCodeMissing = NamedError.create(
-  "ProviderAuthOauthCodeMissing",
-  z.object({ providerID: ProviderID.zod }),
-)
+export const OauthCodeMissing = namedSchemaError("ProviderAuthOauthCodeMissing", { providerID: ProviderID })
 
-export const OauthCallbackFailed = NamedError.create("ProviderAuthOauthCallbackFailed", z.object({}))
+export const OauthCallbackFailed = namedSchemaError("ProviderAuthOauthCallbackFailed", {})
 
-export const ValidationFailed = NamedError.create(
-  "ProviderAuthValidationFailed",
-  z.object({
-    field: z.string(),
-    message: z.string(),
-  }),
-)
+export const ValidationFailed = namedSchemaError("ProviderAuthValidationFailed", {
+  field: Schema.String,
+  message: Schema.String,
+})
 
 export type Error =
   | Auth.AuthError

packages/opencode/src/provider/models.ts

@@ -1,7 +1,7 @@
 import { Global } from "../global"
 import { Log } from "../util"
 import path from "path"
-import z from "zod"
+import { Schema } from "effect"
 import { Installation } from "../installation"
 import { Flag } from "../flag/flag"
 import { lazy } from "@/util/lazy"
@@ -21,91 +21,85 @@ const filepath = path.join(
 )
 const ttl = 5 * 60 * 1000
 
-type JsonValue = string | number | boolean | null | { [key: string]: JsonValue } | JsonValue[]
-
-const JsonValue: z.ZodType<JsonValue> = z.lazy(() =>
-  z.union([z.string(), z.number(), z.boolean(), z.null(), z.array(JsonValue), z.record(z.string(), JsonValue)]),
-)
-
-const Cost = z.object({
-  input: z.number(),
-  output: z.number(),
-  cache_read: z.number().optional(),
-  cache_write: z.number().optional(),
-  context_over_200k: z
-    .object({
-      input: z.number(),
-      output: z.number(),
-      cache_read: z.number().optional(),
-      cache_write: z.number().optional(),
-    })
-    .optional(),
+const Cost = Schema.Struct({
+  input: Schema.Number,
+  output: Schema.Number,
+  cache_read: Schema.optional(Schema.Number),
+  cache_write: Schema.optional(Schema.Number),
+  context_over_200k: Schema.optional(
+    Schema.Struct({
+      input: Schema.Number,
+      output: Schema.Number,
+      cache_read: Schema.optional(Schema.Number),
+      cache_write: Schema.optional(Schema.Number),
+    }),
+  ),
 })
 
-export const Model = z.object({
-  id: z.string(),
-  name: z.string(),
-  family: z.string().optional(),
-  release_date: z.string(),
-  attachment: z.boolean(),
-  reasoning: z.boolean(),
-  temperature: z.boolean(),
-  tool_call: z.boolean(),
-  interleaved: z
-    .union([
-      z.literal(true),
-      z
-        .object({
-          field: z.enum(["reasoning_content", "reasoning_details"]),
-        })
-        .strict(),
-    ])
-    .optional(),
-  cost: Cost.optional(),
-  limit: z.object({
-    context: z.number(),
-    input: z.number().optional(),
-    output: z.number(),
+export const Model = Schema.Struct({
+  id: Schema.String,
+  name: Schema.String,
+  family: Schema.optional(Schema.String),
+  release_date: Schema.String,
+  attachment: Schema.Boolean,
+  reasoning: Schema.Boolean,
+  temperature: Schema.Boolean,
+  tool_call: Schema.Boolean,
+  interleaved: Schema.optional(
+    Schema.Union([
+      Schema.Literal(true),
+      Schema.Struct({
+        field: Schema.Literals(["reasoning_content", "reasoning_details"]),
+      }),
+    ]),
+  ),
+  cost: Schema.optional(Cost),
+  limit: Schema.Struct({
+    context: Schema.Number,
+    input: Schema.optional(Schema.Number),
+    output: Schema.Number,
   }),
-  modalities: z
-    .object({
-      input: z.array(z.enum(["text", "audio", "image", "video", "pdf"])),
-      output: z.array(z.enum(["text", "audio", "image", "video", "pdf"])),
-    })
-    .optional(),
-  experimental: z
-    .object({
-      modes: z
-        .record(
-          z.string(),
-          z.object({
-            cost: Cost.optional(),
-            provider: z
-              .object({
-                body: z.record(z.string(), JsonValue).optional(),
-                headers: z.record(z.string(), z.string()).optional(),
-              })
-              .optional(),
+  modalities: Schema.optional(
+    Schema.Struct({
+      input: Schema.Array(Schema.Literals(["text", "audio", "image", "video", "pdf"])),
+      output: Schema.Array(Schema.Literals(["text", "audio", "image", "video", "pdf"])),
+    }),
+  ),
+  experimental: Schema.optional(
+    Schema.Struct({
+      modes: Schema.optional(
+        Schema.Record(
+          Schema.String,
+          Schema.Struct({
+            cost: Schema.optional(Cost),
+            provider: Schema.optional(
+              Schema.Struct({
+                body: Schema.optional(Schema.Record(Schema.String, Schema.MutableJson)),
+                headers: Schema.optional(Schema.Record(Schema.String, Schema.String)),
+              }),
+            ),
           }),
-        )
-        .optional(),
-    })
-    .optional(),
-  status: z.enum(["alpha", "beta", "deprecated"]).optional(),
-  provider: z.object({ npm: z.string().optional(), api: z.string().optional() }).optional(),
+        ),
+      ),
+    }),
+  ),
+  status: Schema.optional(Schema.Literals(["alpha", "beta", "deprecated"])),
+  provider: Schema.optional(
+    Schema.Struct({ npm: Schema.optional(Schema.String), api: Schema.optional(Schema.String) }),
+  ),
 })
-export type Model = z.infer<typeof Model>
+export type Model = Schema.Schema.Type<typeof Model>
 
-export const Provider = z.object({
-  api: z.string().optional(),
-  name: z.string(),
-  env: z.array(z.string()),
-  id: z.string(),
-  npm: z.string().optional(),
-  models: z.record(z.string(), Model),
+export const Provider = Schema.Struct({
+  api: Schema.optional(Schema.String),
+  name: Schema.String,
+  env: Schema.Array(Schema.String),
+  id: Schema.String,
+  npm: Schema.optional(Schema.String),
+  models: Schema.Record(Schema.String, Model),
 })
 
-export type Provider = z.infer<typeof Provider>
+export type Provider = Schema.Schema.Type<typeof Provider>
 
 function url() {
   return Flag.OPENCODE_MODELS_URL || "https://models.dev"

packages/opencode/src/provider/provider.ts

@@ -1,4 +1,3 @@
-import z from "zod"
 import os from "os"
 import fuzzysort from "fuzzysort"
 import { Config } from "../config"
@@ -8,7 +7,6 @@ import { Log } from "../util"
 import { Npm } from "../npm"
 import { Hash } from "@opencode-ai/shared/util/hash"
 import { Plugin } from "../plugin"
-import { NamedError } from "@opencode-ai/shared/util/error"
 import { type LanguageModelV3 } from "@ai-sdk/provider"
 import * as ModelsDev from "./models"
 import { Auth } from "../auth"
@@ -16,6 +14,7 @@ import { Env } from "../env"
 import { InstallationVersion } from "../installation/version"
 import { Flag } from "../flag/flag"
 import { zod } from "@/util/effect-zod"
+import { namedSchemaError } from "@/util/named-schema-error"
 import { iife } from "@/util/iife"
 import { Global } from "../global"
 import path from "path"
@@ -1047,7 +1046,7 @@ export function fromModelsDevProvider(provider: ModelsDev.Provider): Info {
     id: ProviderID.make(provider.id),
     source: "custom",
     name: provider.name,
-    env: provider.env ?? [],
+    env: [...(provider.env ?? [])],
     options: {},
     models,
   }
@@ -1713,18 +1712,12 @@ export function parseModel(model: string) {
   }
 }
 
-export const ModelNotFoundError = NamedError.create(
-  "ProviderModelNotFoundError",
-  z.object({
-    providerID: ProviderID.zod,
-    modelID: ModelID.zod,
-    suggestions: z.array(z.string()).optional(),
-  }),
-)
+export const ModelNotFoundError = namedSchemaError("ProviderModelNotFoundError", {
+  providerID: ProviderID,
+  modelID: ModelID,
+  suggestions: Schema.optional(Schema.Array(Schema.String)),
+})
 
-export const InitError = NamedError.create(
-  "ProviderInitError",
-  z.object({
-    providerID: ProviderID.zod,
-  }),
-)
+export const InitError = namedSchemaError("ProviderInitError", {
+  providerID: ProviderID,
+})

packages/opencode/src/pty/index.ts

@@ -3,13 +3,14 @@ import { Bus } from "@/bus"
 import { InstanceState } from "@/effect"
 import { Instance } from "@/project/instance"
 import type { Proc } from "#pty"
-import z from "zod"
 import { Log } from "../util"
 import { lazy } from "@opencode-ai/shared/util/lazy"
 import { Shell } from "@/shell/shell"
 import { Plugin } from "@/plugin"
 import { PtyID } from "./schema"
-import { Effect, Layer, Context } from "effect"
+import { Effect, Layer, Context, Schema, Types } from "effect"
+import { zod } from "@/util/effect-zod"
+import { withStatics } from "@/util/schema"
 import { EffectBridge } from "@/effect"
 
 const log = Log.create({ service: "pty" })
@@ -53,47 +54,47 @@ const meta = (cursor: number) => {
 
 const pty = lazy(() => import("#pty"))
 
-export const Info = z
-  .object({
-    id: PtyID.zod,
-    title: z.string(),
-    command: z.string(),
-    args: z.array(z.string()),
-    cwd: z.string(),
-    status: z.enum(["running", "exited"]),
-    pid: z.number(),
-  })
-  .meta({ ref: "Pty" })
-
-export type Info = z.infer<typeof Info>
-
-export const CreateInput = z.object({
-  command: z.string().optional(),
-  args: z.array(z.string()).optional(),
-  cwd: z.string().optional(),
-  title: z.string().optional(),
-  env: z.record(z.string(), z.string()).optional(),
+export const Info = Schema.Struct({
+  id: PtyID,
+  title: Schema.String,
+  command: Schema.String,
+  args: Schema.Array(Schema.String),
+  cwd: Schema.String,
+  status: Schema.Literals(["running", "exited"]),
+  pid: Schema.Number,
 })
+  .annotate({ identifier: "Pty" })
+  .pipe(withStatics((s) => ({ zod: zod(s) })))
 
-export type CreateInput = z.infer<typeof CreateInput>
+export type Info = Types.DeepMutable<Schema.Schema.Type<typeof Info>>
 
-export const UpdateInput = z.object({
-  title: z.string().optional(),
-  size: z
-    .object({
-      rows: z.number(),
-      cols: z.number(),
-    })
-    .optional(),
-})
+export const CreateInput = Schema.Struct({
+  command: Schema.optional(Schema.String),
+  args: Schema.optional(Schema.Array(Schema.String)),
+  cwd: Schema.optional(Schema.String),
+  title: Schema.optional(Schema.String),
+  env: Schema.optional(Schema.Record(Schema.String, Schema.String)),
+}).pipe(withStatics((s) => ({ zod: zod(s) })))
 
-export type UpdateInput = z.infer<typeof UpdateInput>
+export type CreateInput = Types.DeepMutable<Schema.Schema.Type<typeof CreateInput>>
+
+export const UpdateInput = Schema.Struct({
+  title: Schema.optional(Schema.String),
+  size: Schema.optional(
+    Schema.Struct({
+      rows: Schema.Number,
+      cols: Schema.Number,
+    }),
+  ),
+}).pipe(withStatics((s) => ({ zod: zod(s) })))
+
+export type UpdateInput = Types.DeepMutable<Schema.Schema.Type<typeof UpdateInput>>
 
 export const Event = {
-  Created: BusEvent.define("pty.created", z.object({ info: Info })),
-  Updated: BusEvent.define("pty.updated", z.object({ info: Info })),
-  Exited: BusEvent.define("pty.exited", z.object({ id: PtyID.zod, exitCode: z.number() })),
-  Deleted: BusEvent.define("pty.deleted", z.object({ id: PtyID.zod })),
+  Created: BusEvent.define("pty.created", Schema.Struct({ info: Info })),
+  Updated: BusEvent.define("pty.updated", Schema.Struct({ info: Info })),
+  Exited: BusEvent.define("pty.exited", Schema.Struct({ id: PtyID, exitCode: Schema.Number })),
+  Deleted: BusEvent.define("pty.deleted", Schema.Struct({ id: PtyID })),
 }
 
 export interface Interface {

packages/opencode/src/question/index.ts

@@ -94,9 +94,9 @@ class Rejected extends Schema.Class<Rejected>("QuestionRejected")({
 }) {}
 
 export const Event = {
-  Asked: BusEvent.define("question.asked", Request.zod),
-  Replied: BusEvent.define("question.replied", zod(Replied)),
-  Rejected: BusEvent.define("question.rejected", zod(Rejected)),
+  Asked: BusEvent.define("question.asked", Request),
+  Replied: BusEvent.define("question.replied", Replied),
+  Rejected: BusEvent.define("question.rejected", Rejected),
 }
 
 export class RejectedError extends Schema.TaggedErrorClass<RejectedError>()("QuestionRejectedError", {}) {
@@ -194,7 +194,7 @@ export const layer = Layer.effect(
       yield* bus.publish(Event.Replied, {
         sessionID: existing.info.sessionID,
         requestID: existing.info.id,
-        answers: input.answers,
+        answers: input.answers.map((a) => [...a]),
       })
       yield* Deferred.succeed(existing.deferred, input.answers)
     })

packages/opencode/src/server/event.ts

@@ -1,7 +1,7 @@
 import { BusEvent } from "@/bus/bus-event"
-import z from "zod"
+import { Schema } from "effect"
 
 export const Event = {
-  Connected: BusEvent.define("server.connected", z.object({})),
-  Disposed: BusEvent.define("global.disposed", z.object({})),
+  Connected: BusEvent.define("server.connected", Schema.Struct({})),
+  Disposed: BusEvent.define("global.disposed", Schema.Struct({})),
 }

packages/opencode/src/server/projectors.ts

@@ -1,4 +1,3 @@
-import z from "zod"
 import sessionProjectors from "../session/projectors"
 import { SyncEvent } from "@/sync"
 import { Session } from "@/session"
@@ -10,7 +9,7 @@ export function initProjectors() {
     projectors: sessionProjectors,
     convertEvent: (type, data) => {
       if (type === "session.updated") {
-        const id = (data as z.infer<typeof Session.Event.Updated.schema>).sessionID
+        const id = (data as SyncEvent.Event<typeof Session.Event.Updated>["data"]).sessionID
         const row = Database.use((db) => db.select().from(SessionTable).where(eq(SessionTable.id, id)).get())
 
         if (!row) return data

packages/opencode/src/server/routes/control/workspace.ts

@@ -3,6 +3,7 @@ import { describeRoute, resolver, validator } from "hono-openapi"
 import z from "zod"
 import { listAdaptors } from "@/control-plane/adaptors"
 import { Workspace } from "@/control-plane/workspace"
+import { zodObject } from "@/util/effect-zod"
 import { Instance } from "@/project/instance"
 import { errors } from "../../error"
 import { lazy } from "@/util/lazy"
@@ -107,7 +108,7 @@ export const WorkspaceRoutes = lazy(() =>
             description: "Workspace status",
             content: {
               "application/json": {
-                schema: resolver(z.array(Workspace.ConnectionStatus)),
+                schema: resolver(z.array(zodObject(Workspace.ConnectionStatus))),
               },
             },
           },

packages/opencode/src/server/routes/global.ts

@@ -1,7 +1,7 @@
 import { Hono, type Context } from "hono"
 import { describeRoute, resolver, validator } from "hono-openapi"
 import { streamSSE } from "hono/streaming"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 import z from "zod"
 import { BusEvent } from "@/bus/bus-event"
 import { SyncEvent } from "@/sync"
@@ -18,7 +18,7 @@ import { errors } from "../error"
 
 const log = Log.create({ service: "server" })
 
-export const GlobalDisposedEvent = BusEvent.define("global.disposed", z.object({}))
+export const GlobalDisposedEvent = BusEvent.define("global.disposed", Schema.Struct({}))
 
 async function streamEvents(c: Context, subscribe: (q: AsyncQueue<string | null>) => () => void) {
   return streamSSE(c, async (stream) => {

packages/opencode/src/server/routes/instance/experimental.ts

@@ -1,6 +1,7 @@
 import { Hono } from "hono"
 import { describeRoute, validator, resolver } from "hono-openapi"
 import z from "zod"
+import * as EffectZod from "@/util/effect-zod"
 import { ProviderID, ModelID } from "@/provider/schema"
 import { ToolRegistry } from "@/tool"
 import { Worktree } from "@/worktree"
@@ -213,7 +214,7 @@ export const ExperimentalRoutes = lazy(() =>
           tools.map((t) => ({
             id: t.id,
             description: t.description,
-            parameters: z.toJSONSchema(t.parameters),
+            parameters: EffectZod.toJsonSchema(t.parameters),
           })),
         )
       },

packages/opencode/src/server/routes/instance/pty.ts

@@ -23,7 +23,7 @@ export function PtyRoutes(upgradeWebSocket: UpgradeWebSocket) {
             description: "List of sessions",
             content: {
               "application/json": {
-                schema: resolver(Pty.Info.array()),
+                schema: resolver(Pty.Info.zod.array()),
               },
             },
           },
@@ -46,18 +46,18 @@ export function PtyRoutes(upgradeWebSocket: UpgradeWebSocket) {
             description: "Created session",
             content: {
               "application/json": {
-                schema: resolver(Pty.Info),
+                schema: resolver(Pty.Info.zod),
               },
             },
           },
           ...errors(400),
         },
       }),
-      validator("json", Pty.CreateInput),
+      validator("json", Pty.CreateInput.zod),
       async (c) =>
         jsonRequest("PtyRoutes.create", c, function* () {
           const pty = yield* Pty.Service
-          return yield* pty.create(c.req.valid("json"))
+          return yield* pty.create(c.req.valid("json") as Pty.CreateInput)
         }),
     )
     .get(
@@ -71,7 +71,7 @@ export function PtyRoutes(upgradeWebSocket: UpgradeWebSocket) {
             description: "Session info",
             content: {
               "application/json": {
-                schema: resolver(Pty.Info),
+                schema: resolver(Pty.Info.zod),
               },
             },
           },
@@ -105,7 +105,7 @@ export function PtyRoutes(upgradeWebSocket: UpgradeWebSocket) {
             description: "Updated session",
             content: {
               "application/json": {
-                schema: resolver(Pty.Info),
+                schema: resolver(Pty.Info.zod),
               },
             },
           },
@@ -113,11 +113,11 @@ export function PtyRoutes(upgradeWebSocket: UpgradeWebSocket) {
         },
       }),
       validator("param", z.object({ ptyID: PtyID.zod })),
-      validator("json", Pty.UpdateInput),
+      validator("json", Pty.UpdateInput.zod),
       async (c) =>
         jsonRequest("PtyRoutes.update", c, function* () {
           const pty = yield* Pty.Service
-          return yield* pty.update(c.req.valid("param").ptyID, c.req.valid("json"))
+          return yield* pty.update(c.req.valid("param").ptyID, c.req.valid("json") as Pty.UpdateInput)
         }),
     )
     .delete(

packages/opencode/src/server/routes/instance/tui.ts

@@ -1,9 +1,12 @@
 import { Hono, type Context } from "hono"
 import { describeRoute, validator, resolver } from "hono-openapi"
+import { Schema } from "effect"
 import z from "zod"
 import { Bus } from "@/bus"
 import { Session } from "@/session"
+import type { SessionID } from "@/session/schema"
 import { TuiEvent } from "@/cli/cmd/tui/event"
+import { zodObject } from "@/util/effect-zod"
 import { AsyncQueue } from "@/util/queue"
 import { errors } from "../../error"
 import { lazy } from "@/util/lazy"
@@ -96,9 +99,9 @@ export const TuiRoutes = lazy(() =>
           ...errors(400),
         },
       }),
-      validator("json", TuiEvent.PromptAppend.properties),
+      validator("json", zodObject(TuiEvent.PromptAppend.properties)),
       async (c) => {
-        await Bus.publish(TuiEvent.PromptAppend, c.req.valid("json"))
+        await Bus.publish(TuiEvent.PromptAppend, c.req.valid("json") as { text: string })
         return c.json(true)
       },
     )
@@ -305,9 +308,12 @@ export const TuiRoutes = lazy(() =>
           },
         },
       }),
-      validator("json", TuiEvent.ToastShow.properties),
+      validator("json", zodObject(TuiEvent.ToastShow.properties)),
       async (c) => {
-        await Bus.publish(TuiEvent.ToastShow, c.req.valid("json"))
+        await Bus.publish(
+          TuiEvent.ToastShow,
+          c.req.valid("json") as Schema.Schema.Type<typeof TuiEvent.ToastShow.properties>,
+        )
         return c.json(true)
       },
     )
@@ -336,7 +342,7 @@ export const TuiRoutes = lazy(() =>
             return z
               .object({
                 type: z.literal(def.type),
-                properties: def.properties,
+                properties: zodObject(def.properties),
               })
               .meta({
                 ref: `Event.${def.type}`,
@@ -345,8 +351,9 @@ export const TuiRoutes = lazy(() =>
         ),
       ),
       async (c) => {
-        const evt = c.req.valid("json")
-        await Bus.publish(Object.values(TuiEvent).find((def) => def.type === evt.type)!, evt.properties)
+        const evt = c.req.valid("json") as { type: string; properties: Record<string, unknown> }
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        await Bus.publish(Object.values(TuiEvent).find((def) => def.type === evt.type)! as any, evt.properties as any)
         return c.json(true)
       },
     )
@@ -368,9 +375,9 @@ export const TuiRoutes = lazy(() =>
           ...errors(400, 404),
         },
       }),
-      validator("json", TuiEvent.SessionSelect.properties),
+      validator("json", zodObject(TuiEvent.SessionSelect.properties)),
       async (c) => {
-        const { sessionID } = c.req.valid("json")
+        const { sessionID } = c.req.valid("json") as { sessionID: SessionID }
         await runRequest(
           "TuiRoutes.sessionSelect",
           c,

packages/opencode/src/session/compaction.ts

@@ -13,7 +13,7 @@ import { Plugin } from "@/plugin"
 import { Config } from "@/config"
 import { NotFoundError } from "@/storage"
 import { ModelID, ProviderID } from "@/provider/schema"
-import { Effect, Layer, Context } from "effect"
+import { Effect, Layer, Context, Schema } from "effect"
 import { InstanceState } from "@/effect"
 import { isOverflow as overflow, usable } from "./overflow"
 import { makeRuntime } from "@/effect/run-service"
@@ -24,8 +24,8 @@ const log = Log.create({ service: "session.compaction" })
 export const Event = {
   Compacted: BusEvent.define(
     "session.compacted",
-    z.object({
-      sessionID: SessionID.zod,
+    Schema.Struct({
+      sessionID: SessionID,
     }),
   ),
 }

packages/opencode/src/session/message-v2.ts

@@ -17,7 +17,7 @@ import type { Provider } from "@/provider"
 import { ModelID, ProviderID } from "@/provider/schema"
 import { Effect, Schema, Types } from "effect"
 import { zod, ZodOverride } from "@/util/effect-zod"
-import { withStatics } from "@/util/schema"
+import { NonNegativeInt, withStatics } from "@/util/schema"
 import { namedSchemaError } from "@/util/named-schema-error"
 import { EffectLogger } from "@/effect"
 
@@ -64,9 +64,7 @@ export class OutputFormatText extends Schema.Class<OutputFormatText>("OutputForm
 export class OutputFormatJsonSchema extends Schema.Class<OutputFormatJsonSchema>("OutputFormatJsonSchema")({
   type: Schema.Literal("json_schema"),
   schema: Schema.Record(Schema.String, Schema.Any).annotate({ identifier: "JSONSchema" }),
-  retryCount: Schema.Number.check(Schema.isInt())
-    .check(Schema.isGreaterThanOrEqualTo(0))
-    .pipe(Schema.optional, Schema.withDecodingDefault(Effect.succeed(2))),
+  retryCount: NonNegativeInt.pipe(Schema.optional, Schema.withDecodingDefault(Effect.succeed(2))),
 }) {
   static readonly zod = zod(this)
 }
@@ -138,8 +136,8 @@ export type ReasoningPart = Types.DeepMutable<Schema.Schema.Type<typeof Reasonin
 const filePartSourceBase = {
   text: Schema.Struct({
     value: Schema.String,
-    start: Schema.Number.check(Schema.isInt()),
-    end: Schema.Number.check(Schema.isInt()),
+    start: Schema.Int,
+    end: Schema.Int,
   }).annotate({ identifier: "FilePartSourceText" }),
 }
 
@@ -157,7 +155,7 @@ export const SymbolSource = Schema.Struct({
   path: Schema.String,
   range: LSP.Range,
   name: Schema.String,
-  kind: Schema.Number.check(Schema.isInt()),
+  kind: Schema.Int,
 })
   .annotate({ identifier: "SymbolSource" })
   .pipe(withStatics((s) => ({ zod: zod(s) })))
@@ -196,8 +194,8 @@ export const AgentPart = Schema.Struct({
   source: Schema.optional(
     Schema.Struct({
       value: Schema.String,
-      start: Schema.Number.check(Schema.isInt()),
-      end: Schema.Number.check(Schema.isInt()),
+      start: Schema.Int,
+      end: Schema.Int,
     }),
   ),
 })
@@ -501,8 +499,8 @@ export const AgentPartInput = Schema.Struct({
   source: Schema.optional(
     Schema.Struct({
       value: Schema.String,
-      start: Schema.Number.check(Schema.isInt()),
-      end: Schema.Number.check(Schema.isInt()),
+      start: Schema.Int,
+      end: Schema.Int,
     }),
   ),
 })
@@ -576,54 +574,62 @@ export const Info = Object.assign(_Info, {
 })
 export type Info = User | Assistant
 
+const UpdatedEventSchema = Schema.Struct({
+  sessionID: SessionID,
+  info: _Info,
+})
+
+const RemovedEventSchema = Schema.Struct({
+  sessionID: SessionID,
+  messageID: MessageID,
+})
+
+const PartUpdatedEventSchema = Schema.Struct({
+  sessionID: SessionID,
+  part: _Part,
+  time: Schema.Number,
+})
+
+const PartRemovedEventSchema = Schema.Struct({
+  sessionID: SessionID,
+  messageID: MessageID,
+  partID: PartID,
+})
+
 export const Event = {
   Updated: SyncEvent.define({
     type: "message.updated",
     version: 1,
     aggregate: "sessionID",
-    schema: z.object({
-      sessionID: SessionID.zod,
-      info: Info.zod,
-    }),
+    schema: UpdatedEventSchema,
   }),
   Removed: SyncEvent.define({
     type: "message.removed",
     version: 1,
     aggregate: "sessionID",
-    schema: z.object({
-      sessionID: SessionID.zod,
-      messageID: MessageID.zod,
-    }),
+    schema: RemovedEventSchema,
   }),
   PartUpdated: SyncEvent.define({
     type: "message.part.updated",
     version: 1,
     aggregate: "sessionID",
-    schema: z.object({
-      sessionID: SessionID.zod,
-      part: Part.zod,
-      time: z.number(),
-    }),
+    schema: PartUpdatedEventSchema,
   }),
   PartDelta: BusEvent.define(
     "message.part.delta",
-    z.object({
-      sessionID: SessionID.zod,
-      messageID: MessageID.zod,
-      partID: PartID.zod,
-      field: z.string(),
-      delta: z.string(),
+    Schema.Struct({
+      sessionID: SessionID,
+      messageID: MessageID,
+      partID: PartID,
+      field: Schema.String,
+      delta: Schema.String,
     }),
   ),
   PartRemoved: SyncEvent.define({
     type: "message.part.removed",
     version: 1,
     aggregate: "sessionID",
-    schema: z.object({
-      sessionID: SessionID.zod,
-      messageID: MessageID.zod,
-      partID: PartID.zod,
-    }),
+    schema: PartRemovedEventSchema,
   }),
 }
 

packages/opencode/src/session/projectors.ts

@@ -71,7 +71,7 @@ export default [
     const info = data.info
     const row = db
       .update(SessionTable)
-      .set(toPartialRow(info))
+      .set(toPartialRow(info as Session.Patch))
       .where(eq(SessionTable.id, data.sessionID))
       .returning()
       .get()

packages/opencode/src/session/prompt.ts

@@ -1,6 +1,7 @@
 import path from "path"
 import os from "os"
 import z from "zod"
+import * as EffectZod from "@/util/effect-zod"
 import { SessionID, MessageID, PartID } from "./schema"
 import { MessageV2 } from "./message-v2"
 import { Log } from "../util"
@@ -405,7 +406,7 @@ NOTE: At any point in time through this workflow you should feel free to ask the
         providerID: input.model.providerID,
         agent: input.agent,
       })) {
-        const schema = ProviderTransform.schema(input.model, z.toJSONSchema(item.parameters))
+        const schema = ProviderTransform.schema(input.model, EffectZod.toJsonSchema(item.parameters))
         tools[item.id] = tool({
           description: item.description,
           inputSchema: jsonSchema(schema),

packages/opencode/src/session/session.ts

@@ -15,7 +15,6 @@ import { PartTable, SessionTable } from "./session.sql"
 import { ProjectTable } from "../project/project.sql"
 import { Storage } from "@/storage"
 import { Log } from "../util"
-import { updateSchema } from "../util/update-schema"
 import { MessageV2 } from "./message-v2"
 import { Instance } from "../project/instance"
 import { InstanceState } from "@/effect"
@@ -28,7 +27,7 @@ import type { Provider } from "@/provider"
 import { Permission } from "@/permission"
 import { Global } from "@/global"
 import { Effect, Layer, Option, Context, Schema, Types } from "effect"
-import { zod, zodObject } from "@/util/effect-zod"
+import { zod } from "@/util/effect-zod"
 import { withStatics } from "@/util/schema"
 
 const log = Log.create({ service: "session" })
@@ -215,54 +214,77 @@ export const MessagesInput = Schema.Struct({
   limit: Schema.optional(Schema.Number),
 }).pipe(withStatics((s) => ({ zod: zod(s) })))
 
+const CreatedEventSchema = Schema.Struct({
+  sessionID: SessionID,
+  info: Info,
+})
+
+const UpdatedShare = Schema.Struct({
+  url: Schema.optional(Schema.NullOr(Schema.String)),
+})
+
+const UpdatedTime = Schema.Struct({
+  created: Schema.optional(Schema.NullOr(Schema.Number)),
+  updated: Schema.optional(Schema.NullOr(Schema.Number)),
+  compacting: Schema.optional(Schema.NullOr(Schema.Number)),
+  archived: Schema.optional(Schema.NullOr(Schema.Number)),
+})
+
+const UpdatedInfo = Schema.Struct({
+  id: Schema.optional(Schema.NullOr(SessionID)),
+  slug: Schema.optional(Schema.NullOr(Schema.String)),
+  projectID: Schema.optional(Schema.NullOr(ProjectID)),
+  workspaceID: Schema.optional(Schema.NullOr(WorkspaceID)),
+  directory: Schema.optional(Schema.NullOr(Schema.String)),
+  parentID: Schema.optional(Schema.NullOr(SessionID)),
+  summary: Schema.optional(Schema.NullOr(Summary)),
+  share: Schema.optional(UpdatedShare),
+  title: Schema.optional(Schema.NullOr(Schema.String)),
+  version: Schema.optional(Schema.NullOr(Schema.String)),
+  time: Schema.optional(UpdatedTime),
+  permission: Schema.optional(Schema.NullOr(Permission.Ruleset)),
+  revert: Schema.optional(Schema.NullOr(Revert)),
+})
+
+const UpdatedEventSchema = Schema.Struct({
+  sessionID: SessionID,
+  info: UpdatedInfo,
+})
+
 export const Event = {
   Created: SyncEvent.define({
     type: "session.created",
     version: 1,
     aggregate: "sessionID",
-    schema: z.object({
-      sessionID: SessionID.zod,
-      info: Info.zod,
-    }),
+    schema: CreatedEventSchema,
   }),
   Updated: SyncEvent.define({
     type: "session.updated",
     version: 1,
     aggregate: "sessionID",
-    schema: z.object({
-      sessionID: SessionID.zod,
-      info: updateSchema(zodObject(Info)).extend({
-        share: updateSchema(zodObject(Share)).optional(),
-        time: updateSchema(zodObject(Time)).optional(),
-      }),
-    }),
-    busSchema: z.object({
-      sessionID: SessionID.zod,
-      info: Info.zod,
-    }),
+    schema: UpdatedEventSchema,
+    busSchema: CreatedEventSchema,
   }),
   Deleted: SyncEvent.define({
     type: "session.deleted",
     version: 1,
     aggregate: "sessionID",
-    schema: z.object({
-      sessionID: SessionID.zod,
-      info: Info.zod,
-    }),
+    schema: CreatedEventSchema,
   }),
   Diff: BusEvent.define(
     "session.diff",
-    z.object({
-      sessionID: SessionID.zod,
-      diff: Snapshot.FileDiff.zod.array(),
+    Schema.Struct({
+      sessionID: SessionID,
+      diff: Schema.Array(Snapshot.FileDiff),
     }),
   ),
   Error: BusEvent.define(
     "session.error",
-    z.object({
-      sessionID: SessionID.zod.optional(),
-      // z.lazy defers access to break circular dep: session → message-v2 → provider → plugin → session
-      error: z.lazy(() => (MessageV2.Assistant.zod as unknown as z.ZodObject<any>).shape.error),
+    Schema.Struct({
+      sessionID: Schema.optional(SessionID),
+      // Reuses MessageV2.Assistant.fields.error (already Schema.optional) so
+      // the derived zod keeps the same discriminated-union shape on the bus.
+      error: MessageV2.Assistant.fields.error,
     }),
   ),
 }
@@ -394,7 +416,7 @@ export interface Interface {
 
 export class Service extends Context.Service<Service, Interface>()("@opencode/Session") {}
 
-type Patch = z.infer<typeof Event.Updated.schema>["info"]
+export type Patch = Types.DeepMutable<SyncEvent.Event<typeof Event.Updated>["data"]["info"]>
 
 const db = <T>(fn: (d: Parameters<typeof Database.use>[0] extends (trx: infer D) => any ? D : never) => T) =>
   Effect.sync(() => Database.use(fn))

packages/opencode/src/session/status.ts

@@ -28,16 +28,16 @@ export type Info = Schema.Schema.Type<typeof Info>
 export const Event = {
   Status: BusEvent.define(
     "session.status",
-    z.object({
-      sessionID: SessionID.zod,
-      status: Info.zod,
+    Schema.Struct({
+      sessionID: SessionID,
+      status: Info,
     }),
   ),
   // deprecated
   Idle: BusEvent.define(
     "session.idle",
-    z.object({
-      sessionID: SessionID.zod,
+    Schema.Struct({
+      sessionID: SessionID,
     }),
   ),
 }

packages/opencode/src/session/todo.ts

@@ -22,9 +22,9 @@ export type Info = Schema.Schema.Type<typeof Info>
 export const Event = {
   Updated: BusEvent.define(
     "todo.updated",
-    z.object({
-      sessionID: SessionID.zod,
-      todos: z.array(Info.zod),
+    Schema.Struct({
+      sessionID: SessionID,
+      todos: Schema.Array(Info),
     }),
   ),
 }

packages/opencode/src/share/share-next.ts

@@ -181,7 +181,7 @@ export const layer = Layer.effect(
 
         yield* watch(Session.Event.Updated, (evt) =>
           Effect.gen(function* () {
-            const info = yield* session.get(evt.properties.sessionID)
+            const info = evt.properties.info
             yield* sync(info.id, [{ type: "session", data: info }])
           }),
         )

packages/opencode/src/sync/index.ts

@@ -1,5 +1,4 @@
 import z from "zod"
-import type { ZodObject } from "zod"
 import { Database, eq } from "@/storage"
 import { GlobalBus } from "@/bus/global"
 import { Bus as ProjectBus } from "@/bus"
@@ -9,34 +8,48 @@ import { EventSequenceTable, EventTable } from "./event.sql"
 import { WorkspaceContext } from "@/control-plane/workspace-context"
 import { EventID } from "./schema"
 import { Flag } from "@/flag/flag"
+import { Schema as EffectSchema } from "effect"
+import { zodObject } from "@/util/effect-zod"
+import type { DeepMutable } from "@/util/schema"
 
-export type Definition = {
-  type: string
+// Keep `Event["data"]` mutable because projectors mutate the persisted shape
+// when writing to the database. Bus payloads (`Properties`) stay readonly —
+// subscribers only read.
+
+export type Definition<
+  Type extends string = string,
+  Schema extends EffectSchema.Top = EffectSchema.Top,
+  BusSchema extends EffectSchema.Top = Schema,
+> = {
+  type: Type
   version: number
   aggregate: string
-  schema: z.ZodObject
-
-  // This is temporary and only exists for compatibility with bus
-  // event definitions
-  properties: z.ZodObject
+  schema: Schema
+  // Bus event payload schema. Defaults to `schema` unless `busSchema` was
+  // passed at definition time (see `session.updated`, whose projector
+  // expands the persisted data to a `{ sessionID, info }` bus payload).
+  properties: BusSchema
 }
 
 export type Event<Def extends Definition = Definition> = {
   id: string
   seq: number
   aggregateID: string
-  data: z.infer<Def["schema"]>
+  data: DeepMutable<EffectSchema.Schema.Type<Def["schema"]>>
 }
 
+export type Properties<Def extends Definition = Definition> = EffectSchema.Schema.Type<Def["properties"]>
+
 export type SerializedEvent<Def extends Definition = Definition> = Event<Def> & { type: string }
 
 type ProjectorFunc = (db: Database.TxOrDb, data: unknown) => void
+type ConvertEvent = (type: string, data: Event["data"]) => unknown | Promise<unknown>
 
 export const registry = new Map<string, Definition>()
 let projectors: Map<Definition, ProjectorFunc> | undefined
 const versions = new Map<string, number>()
 let frozen = false
-let convertEvent: (type: string, event: Event["data"]) => Promise<Record<string, unknown>> | Record<string, unknown>
+let convertEvent: ConvertEvent
 
 export function reset() {
   frozen = false
@@ -44,7 +57,7 @@ export function reset() {
   convertEvent = (_, data) => data
 }
 
-export function init(input: { projectors: Array<[Definition, ProjectorFunc]>; convertEvent?: typeof convertEvent }) {
+export function init(input: { projectors: Array<[Definition, ProjectorFunc]>; convertEvent?: ConvertEvent }) {
   projectors = new Map(input.projectors)
 
   // Install all the latest event defs to the bus. We only ever emit
@@ -54,13 +67,13 @@ export function init(input: { projectors: Array<[Definition, ProjectorFunc]>; co
   for (let [type, version] of versions.entries()) {
     let def = registry.get(versionedType(type, version))!
 
-    BusEvent.define(def.type, def.properties || def.schema)
+    BusEvent.define(def.type, def.properties)
   }
 
   // Freeze the system so it clearly errors if events are defined
   // after `init` which would cause bugs
   frozen = true
-  convertEvent = input.convertEvent || ((_, data) => data)
+  convertEvent = input.convertEvent ?? ((_, data) => data)
 }
 
 export function versionedType<A extends string>(type: A): A
@@ -72,9 +85,15 @@ export function versionedType(type: string, version?: number) {
 export function define<
   Type extends string,
   Agg extends string,
-  Schema extends ZodObject<Record<Agg, z.ZodType<string>>>,
-  BusSchema extends ZodObject = Schema,
->(input: { type: Type; version: number; aggregate: Agg; schema: Schema; busSchema?: BusSchema }) {
+  Schema extends EffectSchema.Top,
+  BusSchema extends EffectSchema.Top = Schema,
+>(input: {
+  type: Type
+  version: number
+  aggregate: Agg
+  schema: Schema
+  busSchema?: BusSchema
+}): Definition<Type, Schema, BusSchema> {
   if (frozen) {
     throw new Error("Error defining sync event: sync system has been frozen")
   }
@@ -84,7 +103,7 @@ export function define<
     version: input.version,
     aggregate: input.aggregate,
     schema: input.schema,
-    properties: input.busSchema ? input.busSchema : input.schema,
+    properties: (input.busSchema ?? input.schema) as BusSchema,
   }
 
   versions.set(def.type, Math.max(def.version, versions.get(def.type) || 0))
@@ -141,12 +160,11 @@ function process<Def extends Definition>(def: Def, event: Event<Def>, options: {
     Database.effect(() => {
       if (options?.publish) {
         const result = convertEvent(def.type, event.data)
+        const publish = (data: unknown) => ProjectBus.publish(def, data as Properties<Def>)
         if (result instanceof Promise) {
-          void result.then((data) => {
-            void ProjectBus.publish({ type: def.type, properties: def.schema }, data)
-          })
+          void result.then(publish)
         } else {
-          void ProjectBus.publish({ type: def.type, properties: def.schema }, result)
+          void publish(result)
         }
 
         GlobalBus.emit("event", {
@@ -266,7 +284,7 @@ export function payloads() {
           id: z.string(),
           seq: z.number(),
           aggregateID: z.literal(def.aggregate),
-          data: def.schema,
+          data: zodObject(def.schema),
         })
         .meta({
           ref: `SyncEvent.${def.type}`,

packages/opencode/src/tool/apply_patch.ts

@@ -1,6 +1,5 @@
-import z from "zod"
 import * as path from "path"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 import * as Tool from "./tool"
 import { Bus } from "../bus"
 import { FileWatcher } from "../file/watcher"
@@ -16,8 +15,8 @@ import { File } from "../file"
 import { Format } from "../format"
 import * as Bom from "@/util/bom"
 
-const PatchParams = z.object({
-  patchText: z.string().describe("The full patch text that describes all changes to be made"),
+export const Parameters = Schema.Struct({
+  patchText: Schema.String.annotate({ description: "The full patch text that describes all changes to be made" }),
 })
 
 export const ApplyPatchTool = Tool.define(
@@ -28,7 +27,10 @@ export const ApplyPatchTool = Tool.define(
     const format = yield* Format.Service
     const bus = yield* Bus.Service
 
-    const run = Effect.fn("ApplyPatchTool.execute")(function* (params: z.infer<typeof PatchParams>, ctx: Tool.Context) {
+    const run = Effect.fn("ApplyPatchTool.execute")(function* (
+      params: Schema.Schema.Type<typeof Parameters>,
+      ctx: Tool.Context,
+    ) {
       if (!params.patchText) {
         return yield* Effect.fail(new Error("patchText is required"))
       }
@@ -297,8 +299,9 @@ export const ApplyPatchTool = Tool.define(
 
     return {
       description: DESCRIPTION,
-      parameters: PatchParams,
-      execute: (params: z.infer<typeof PatchParams>, ctx: Tool.Context) => run(params, ctx).pipe(Effect.orDie),
+      parameters: Parameters,
+      execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) =>
+        run(params, ctx).pipe(Effect.orDie),
     }
   }),
 )

packages/opencode/src/tool/bash.ts

@@ -1,4 +1,4 @@
-import z from "zod"
+import { Schema } from "effect"
 import os from "os"
 import { createWriteStream } from "node:fs"
 import * as Tool from "./tool"
@@ -50,20 +50,16 @@ const FILES = new Set([
 const FLAGS = new Set(["-destination", "-literalpath", "-path"])
 const SWITCHES = new Set(["-confirm", "-debug", "-force", "-nonewline", "-recurse", "-verbose", "-whatif"])
 
-const Parameters = z.object({
-  command: z.string().describe("The command to execute"),
-  timeout: z.number().describe("Optional timeout in milliseconds").optional(),
-  workdir: z
-    .string()
-    .describe(
-      `The working directory to run the command in. Defaults to the current directory. Use this instead of 'cd' commands.`,
-    )
-    .optional(),
-  description: z
-    .string()
-    .describe(
+export const Parameters = Schema.Struct({
+  command: Schema.String.annotate({ description: "The command to execute" }),
+  timeout: Schema.optional(Schema.Number).annotate({ description: "Optional timeout in milliseconds" }),
+  workdir: Schema.optional(Schema.String).annotate({
+    description: `The working directory to run the command in. Defaults to the current directory. Use this instead of 'cd' commands.`,
+  }),
+  description: Schema.String.annotate({
+    description:
       "Clear, concise description of what this command does in 5-10 words. Examples:\nInput: ls\nOutput: Lists files in current directory\n\nInput: git status\nOutput: Shows working tree status\n\nInput: npm install\nOutput: Installs package dependencies\n\nInput: mkdir foo\nOutput: Creates directory 'foo'",
-    ),
+  }),
 })
 
 type Part = {
@@ -587,7 +583,7 @@ export const BashTool = Tool.define(
             .replaceAll("${maxLines}", String(Truncate.MAX_LINES))
             .replaceAll("${maxBytes}", String(Truncate.MAX_BYTES)),
           parameters: Parameters,
-          execute: (params: z.infer<typeof Parameters>, ctx: Tool.Context) =>
+          execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) =>
             Effect.gen(function* () {
               const cwd = params.workdir
                 ? yield* resolvePath(params.workdir, Instance.directory, shell)

packages/opencode/src/tool/codesearch.ts

@@ -1,10 +1,24 @@
-import z from "zod"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 import { HttpClient } from "effect/unstable/http"
 import * as Tool from "./tool"
 import * as McpExa from "./mcp-exa"
 import DESCRIPTION from "./codesearch.txt"
 
+export const Parameters = Schema.Struct({
+  query: Schema.String.annotate({
+    description:
+      "Search query to find relevant context for APIs, Libraries, and SDKs. For example, 'React useState hook examples', 'Python pandas dataframe filtering', 'Express.js middleware', 'Next js partial prerendering configuration'",
+  }),
+  tokensNum: Schema.Finite.pipe(
+    Schema.check(Schema.isGreaterThanOrEqualTo(1000), Schema.isLessThanOrEqualTo(50000)),
+    Schema.withDecodingDefaultTypeKey(Effect.succeed(5000)),
+  )
+    .annotate({
+      description:
+        "Number of tokens to return (1000-50000). Default is 5000 tokens. Adjust this value based on how much context you need - use lower values for focused queries and higher values for comprehensive documentation.",
+    }),
+})
+
 export const CodeSearchTool = Tool.define(
   "codesearch",
   Effect.gen(function* () {
@@ -12,22 +26,8 @@ export const CodeSearchTool = Tool.define(
 
     return {
       description: DESCRIPTION,
-      parameters: z.object({
-        query: z
-          .string()
-          .describe(
-            "Search query to find relevant context for APIs, Libraries, and SDKs. For example, 'React useState hook examples', 'Python pandas dataframe filtering', 'Express.js middleware', 'Next js partial prerendering configuration'",
-          ),
-        tokensNum: z
-          .number()
-          .min(1000)
-          .max(50000)
-          .default(5000)
-          .describe(
-            "Number of tokens to return (1000-50000). Default is 5000 tokens. Adjust this value based on how much context you need - use lower values for focused queries and higher values for comprehensive documentation.",
-          ),
-      }),
-      execute: (params: { query: string; tokensNum: number }, ctx: Tool.Context) =>
+      parameters: Parameters,
+      execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) =>
         Effect.gen(function* () {
           yield* ctx.ask({
             permission: "codesearch",
@@ -45,7 +45,7 @@ export const CodeSearchTool = Tool.define(
             McpExa.CodeArgs,
             {
               query: params.query,
-              tokensNum: params.tokensNum || 5000,
+              tokensNum: params.tokensNum,
             },
             "30 seconds",
           )

packages/opencode/src/tool/edit.ts

@@ -3,9 +3,8 @@
 // https://github.com/google-gemini/gemini-cli/blob/main/packages/core/src/utils/editCorrector.ts
 // https://github.com/cline/cline/blob/main/evals/diff-edits/diff-apply/diff-06-26-25.ts
 
-import z from "zod"
 import * as path from "path"
-import { Effect, Semaphore } from "effect"
+import { Effect, Schema, Semaphore } from "effect"
 import * as Tool from "./tool"
 import { LSP } from "../lsp"
 import { createTwoFilesPatch, diffLines } from "diff"
@@ -45,11 +44,15 @@ function lock(filePath: string) {
   return next
 }
 
-const Parameters = z.object({
-  filePath: z.string().describe("The absolute path to the file to modify"),
-  oldString: z.string().describe("The text to replace"),
-  newString: z.string().describe("The text to replace it with (must be different from oldString)"),
-  replaceAll: z.boolean().optional().describe("Replace all occurrences of oldString (default false)"),
+export const Parameters = Schema.Struct({
+  filePath: Schema.String.annotate({ description: "The absolute path to the file to modify" }),
+  oldString: Schema.String.annotate({ description: "The text to replace" }),
+  newString: Schema.String.annotate({
+    description: "The text to replace it with (must be different from oldString)",
+  }),
+  replaceAll: Schema.optional(Schema.Boolean).annotate({
+    description: "Replace all occurrences of oldString (default false)",
+  }),
 })
 
 export const EditTool = Tool.define(
@@ -63,7 +66,7 @@ export const EditTool = Tool.define(
     return {
       description: DESCRIPTION,
       parameters: Parameters,
-      execute: (params: z.infer<typeof Parameters>, ctx: Tool.Context) =>
+      execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) =>
         Effect.gen(function* () {
           if (!params.filePath) {
             throw new Error("filePath is required")

packages/opencode/src/tool/glob.ts

@@ -1,6 +1,5 @@
 import path from "path"
-import z from "zod"
-import { Effect, Option } from "effect"
+import { Effect, Option, Schema } from "effect"
 import * as Stream from "effect/Stream"
 import { InstanceState } from "@/effect"
 import { AppFileSystem } from "@opencode-ai/shared/filesystem"
@@ -9,6 +8,13 @@ import { assertExternalDirectoryEffect } from "./external-directory"
 import DESCRIPTION from "./glob.txt"
 import * as Tool from "./tool"
 
+export const Parameters = Schema.Struct({
+  pattern: Schema.String.annotate({ description: "The glob pattern to match files against" }),
+  path: Schema.optional(Schema.String).annotate({
+    description: `The directory to search in. If not specified, the current working directory will be used. IMPORTANT: Omit this field to use the default directory. DO NOT enter "undefined" or "null" - simply omit it for the default behavior. Must be a valid directory path if provided.`,
+  }),
+})
+
 export const GlobTool = Tool.define(
   "glob",
   Effect.gen(function* () {
@@ -17,15 +23,7 @@ export const GlobTool = Tool.define(
 
     return {
       description: DESCRIPTION,
-      parameters: z.object({
-        pattern: z.string().describe("The glob pattern to match files against"),
-        path: z
-          .string()
-          .optional()
-          .describe(
-            `The directory to search in. If not specified, the current working directory will be used. IMPORTANT: Omit this field to use the default directory. DO NOT enter "undefined" or "null" - simply omit it for the default behavior. Must be a valid directory path if provided.`,
-          ),
-      }),
+      parameters: Parameters,
       execute: (params: { pattern: string; path?: string }, ctx: Tool.Context) =>
         Effect.gen(function* () {
           const ins = yield* InstanceState.context

packages/opencode/src/tool/grep.ts

@@ -1,5 +1,5 @@
 import path from "path"
-import z from "zod"
+import { Schema } from "effect"
 import { Effect, Option } from "effect"
 import { InstanceState } from "@/effect"
 import { AppFileSystem } from "@opencode-ai/shared/filesystem"
@@ -10,6 +10,16 @@ import * as Tool from "./tool"
 
 const MAX_LINE_LENGTH = 2000
 
+export const Parameters = Schema.Struct({
+  pattern: Schema.String.annotate({ description: "The regex pattern to search for in file contents" }),
+  path: Schema.optional(Schema.String).annotate({
+    description: "The directory to search in. Defaults to the current working directory.",
+  }),
+  include: Schema.optional(Schema.String).annotate({
+    description: 'File pattern to include in the search (e.g. "*.js", "*.{ts,tsx}")',
+  }),
+})
+
 export const GrepTool = Tool.define(
   "grep",
   Effect.gen(function* () {
@@ -18,11 +28,7 @@ export const GrepTool = Tool.define(
 
     return {
       description: DESCRIPTION,
-      parameters: z.object({
-        pattern: z.string().describe("The regex pattern to search for in file contents"),
-        path: z.string().optional().describe("The directory to search in. Defaults to the current working directory."),
-        include: z.string().optional().describe('File pattern to include in the search (e.g. "*.js", "*.{ts,tsx}")'),
-      }),
+      parameters: Parameters,
       execute: (params: { pattern: string; path?: string; include?: string }, ctx: Tool.Context) =>
         Effect.gen(function* () {
           const empty = {

packages/opencode/src/tool/invalid.ts

@@ -1,15 +1,16 @@
-import z from "zod"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 import * as Tool from "./tool"
 
+export const Parameters = Schema.Struct({
+  tool: Schema.String,
+  error: Schema.String,
+})
+
 export const InvalidTool = Tool.define(
   "invalid",
   Effect.succeed({
     description: "Do not use",
-    parameters: z.object({
-      tool: z.string(),
-      error: z.string(),
-    }),
+    parameters: Parameters,
     execute: (params: { tool: string; error: string }) =>
       Effect.succeed({
         title: "Invalid Tool",

packages/opencode/src/tool/lsp.ts

@@ -1,5 +1,4 @@
-import z from "zod"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 import * as Tool from "./tool"
 import path from "path"
 import { LSP } from "../lsp"
@@ -21,6 +20,17 @@ const operations = [
   "outgoingCalls",
 ] as const
 
+export const Parameters = Schema.Struct({
+  operation: Schema.Literals(operations).annotate({ description: "The LSP operation to perform" }),
+  filePath: Schema.String.annotate({ description: "The absolute or relative path to the file" }),
+  line: Schema.Number.check(Schema.isInt())
+    .check(Schema.isGreaterThanOrEqualTo(1))
+    .annotate({ description: "The line number (1-based, as shown in editors)" }),
+  character: Schema.Number.check(Schema.isInt())
+    .check(Schema.isGreaterThanOrEqualTo(1))
+    .annotate({ description: "The character offset (1-based, as shown in editors)" }),
+})
+
 export const LspTool = Tool.define(
   "lsp",
   Effect.gen(function* () {
@@ -29,12 +39,7 @@ export const LspTool = Tool.define(
 
     return {
       description: DESCRIPTION,
-      parameters: z.object({
-        operation: z.enum(operations).describe("The LSP operation to perform"),
-        filePath: z.string().describe("The absolute or relative path to the file"),
-        line: z.number().int().min(1).describe("The line number (1-based, as shown in editors)"),
-        character: z.number().int().min(1).describe("The character offset (1-based, as shown in editors)"),
-      }),
+      parameters: Parameters,
       execute: (
         args: { operation: (typeof operations)[number]; filePath: string; line: number; character: number },
         ctx: Tool.Context,

packages/opencode/src/tool/plan.ts

@@ -1,6 +1,5 @@
-import z from "zod"
 import path from "path"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 import * as Tool from "./tool"
 import { Question } from "../question"
 import { Session } from "../session"
@@ -17,6 +16,8 @@ function getLastModel(sessionID: SessionID) {
   return undefined
 }
 
+export const Parameters = Schema.Struct({})
+
 export const PlanExitTool = Tool.define(
   "plan_exit",
   Effect.gen(function* () {
@@ -26,7 +27,7 @@ export const PlanExitTool = Tool.define(
 
     return {
       description: EXIT_DESCRIPTION,
-      parameters: z.object({}),
+      parameters: Parameters,
       execute: (_params: {}, ctx: Tool.Context) =>
         Effect.gen(function* () {
           const info = yield* session.get(ctx.sessionID)

packages/opencode/src/tool/question.ts

@@ -1,26 +1,25 @@
-import z from "zod"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 import * as Tool from "./tool"
 import { Question } from "../question"
 import DESCRIPTION from "./question.txt"
 
-const parameters = z.object({
-  questions: z.array(Question.Prompt.zod).describe("Questions to ask"),
+export const Parameters = Schema.Struct({
+  questions: Schema.mutable(Schema.Array(Question.Prompt)).annotate({ description: "Questions to ask" }),
 })
 
 type Metadata = {
   answers: ReadonlyArray<Question.Answer>
 }
 
-export const QuestionTool = Tool.define<typeof parameters, Metadata, Question.Service>(
+export const QuestionTool = Tool.define<typeof Parameters, Metadata, Question.Service>(
   "question",
   Effect.gen(function* () {
     const question = yield* Question.Service
 
     return {
       description: DESCRIPTION,
-      parameters,
-      execute: (params: z.infer<typeof parameters>, ctx: Tool.Context<Metadata>) =>
+      parameters: Parameters,
+      execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context<Metadata>) =>
         Effect.gen(function* () {
           const answers = yield* question.ask({
             sessionID: ctx.sessionID,

packages/opencode/src/tool/read.ts

@@ -1,5 +1,4 @@
-import z from "zod"
-import { Effect, Option, Scope } from "effect"
+import { Effect, Option, Schema, Scope } from "effect"
 import { createReadStream } from "fs"
 import * as path from "path"
 import { createInterface } from "readline"
@@ -19,10 +18,19 @@ const MAX_BYTES = 50 * 1024
 const MAX_BYTES_LABEL = `${MAX_BYTES / 1024} KB`
 const SAMPLE_BYTES = 4096
 
-const parameters = z.object({
-  filePath: z.string().describe("The absolute path to the file or directory to read"),
-  offset: z.coerce.number().describe("The line number to start reading from (1-indexed)").optional(),
-  limit: z.coerce.number().describe("The maximum number of lines to read (defaults to 2000)").optional(),
+// `offset` and `limit` were originally `z.coerce.number()` — the runtime
+// coercion was useful when the tool was called from a shell but serves no
+// purpose in the LLM tool-call path (the model emits typed JSON). The JSON
+// Schema output is identical (`type: "number"`), so the LLM view is
+// unchanged; purely CLI-facing uses must now send numbers rather than strings.
+export const Parameters = Schema.Struct({
+  filePath: Schema.String.annotate({ description: "The absolute path to the file or directory to read" }),
+  offset: Schema.optional(Schema.Number).annotate({
+    description: "The line number to start reading from (1-indexed)",
+  }),
+  limit: Schema.optional(Schema.Number).annotate({
+    description: "The maximum number of lines to read (defaults to 2000)",
+  }),
 })
 
 export const ReadTool = Tool.define(
@@ -140,7 +148,10 @@ export const ReadTool = Tool.define(
       return nonPrintableCount / bytes.length > 0.3
     }
 
-    const run = Effect.fn("ReadTool.execute")(function* (params: z.infer<typeof parameters>, ctx: Tool.Context) {
+    const run = Effect.fn("ReadTool.execute")(function* (
+      params: Schema.Schema.Type<typeof Parameters>,
+      ctx: Tool.Context,
+    ) {
       if (params.offset !== undefined && params.offset < 1) {
         return yield* Effect.fail(new Error("offset must be greater than or equal to 1"))
       }
@@ -275,8 +286,9 @@ export const ReadTool = Tool.define(
 
     return {
       description: DESCRIPTION,
-      parameters,
-      execute: (params: z.infer<typeof parameters>, ctx: Tool.Context) => run(params, ctx).pipe(Effect.orDie),
+      parameters: Parameters,
+      execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) =>
+        run(params, ctx).pipe(Effect.orDie),
     }
   }),
 )

packages/opencode/src/tool/registry.ts

@@ -15,7 +15,9 @@ import { SkillTool } from "./skill"
 import * as Tool from "./tool"
 import { Config } from "../config"
 import { type ToolContext as PluginToolContext, type ToolDefinition } from "@opencode-ai/plugin"
+import { Schema } from "effect"
 import z from "zod"
+import { ZodOverride } from "@/util/effect-zod"
 import { Plugin } from "../plugin"
 import { Provider } from "../provider"
 import { ProviderID, type ModelID } from "../provider/schema"
@@ -120,9 +122,17 @@ export const layer: Layer.Layer<
         const custom: Tool.Def[] = []
 
         function fromPlugin(id: string, def: ToolDefinition): Tool.Def {
+          // Plugin tools define their args as a raw Zod shape. Wrap the
+          // derived Zod object in a `Schema.declare` so it slots into the
+          // Schema-typed framework, and annotate with `ZodOverride` so the
+          // walker emits the original Zod object for LLM JSON Schema.
+          const zodParams = z.object(def.args)
+          const parameters = Schema.declare<unknown>((u): u is unknown => zodParams.safeParse(u).success).annotate({
+            [ZodOverride]: zodParams,
+          })
           return {
             id,
-            parameters: z.object(def.args),
+            parameters,
             description: def.description,
             execute: (args, toolCtx) =>
               Effect.gen(function* () {

packages/opencode/src/tool/skill.ts

@@ -1,15 +1,14 @@
 import path from "path"
 import { pathToFileURL } from "url"
-import z from "zod"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 import * as Stream from "effect/Stream"
 import { Ripgrep } from "../file/ripgrep"
 import { Skill } from "../skill"
 import * as Tool from "./tool"
 import DESCRIPTION from "./skill.txt"
 
-const Parameters = z.object({
-  name: z.string().describe("The name of the skill from available_skills"),
+export const Parameters = Schema.Struct({
+  name: Schema.String.annotate({ description: "The name of the skill from available_skills" }),
 })
 
 export const SkillTool = Tool.define(
@@ -21,7 +20,7 @@ export const SkillTool = Tool.define(
     return {
       description: DESCRIPTION,
       parameters: Parameters,
-      execute: (params: z.infer<typeof Parameters>, ctx: Tool.Context) =>
+      execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) =>
         Effect.gen(function* () {
           const info = yield* skill.get(params.name)
           if (!info) {

packages/opencode/src/tool/task.ts

@@ -1,13 +1,12 @@
 import * as Tool from "./tool"
 import DESCRIPTION from "./task.txt"
-import z from "zod"
 import { Session } from "../session"
 import { SessionID, MessageID } from "../session/schema"
 import { MessageV2 } from "../session/message-v2"
 import { Agent } from "../agent/agent"
 import type { SessionPrompt } from "../session/prompt"
 import { Config } from "../config"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 
 export interface TaskPromptOps {
   cancel(sessionID: SessionID): void
@@ -17,17 +16,15 @@ export interface TaskPromptOps {
 
 const id = "task"
 
-const parameters = z.object({
-  description: z.string().describe("A short (3-5 words) description of the task"),
-  prompt: z.string().describe("The task for the agent to perform"),
-  subagent_type: z.string().describe("The type of specialized agent to use for this task"),
-  task_id: z
-    .string()
-    .describe(
+export const Parameters = Schema.Struct({
+  description: Schema.String.annotate({ description: "A short (3-5 words) description of the task" }),
+  prompt: Schema.String.annotate({ description: "The task for the agent to perform" }),
+  subagent_type: Schema.String.annotate({ description: "The type of specialized agent to use for this task" }),
+  task_id: Schema.optional(Schema.String).annotate({
+    description:
       "This should only be set if you mean to resume a previous task (you can pass a prior task_id and the task will continue the same subagent session as before instead of creating a fresh one)",
-    )
-    .optional(),
-  command: z.string().describe("The command that triggered this task").optional(),
+  }),
+  command: Schema.optional(Schema.String).annotate({ description: "The command that triggered this task" }),
 })
 
 export const TaskTool = Tool.define(
@@ -37,7 +34,10 @@ export const TaskTool = Tool.define(
     const config = yield* Config.Service
     const sessions = yield* Session.Service
 
-    const run = Effect.fn("TaskTool.execute")(function* (params: z.infer<typeof parameters>, ctx: Tool.Context) {
+    const run = Effect.fn("TaskTool.execute")(function* (
+      params: Schema.Schema.Type<typeof Parameters>,
+      ctx: Tool.Context,
+    ) {
       const cfg = yield* config.get()
 
       if (!ctx.extra?.bypassAgentCheck) {
@@ -168,8 +168,9 @@ export const TaskTool = Tool.define(
 
     return {
       description: DESCRIPTION,
-      parameters,
-      execute: (params: z.infer<typeof parameters>, ctx: Tool.Context) => run(params, ctx).pipe(Effect.orDie),
+      parameters: Parameters,
+      execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) =>
+        run(params, ctx).pipe(Effect.orDie),
     }
   }),
 )

packages/opencode/src/tool/todo.ts

@@ -1,39 +1,36 @@
-import z from "zod"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 import * as Tool from "./tool"
 import DESCRIPTION_WRITE from "./todowrite.txt"
 import { Todo } from "../session/todo"
 
-// Parameters are kept inline rather than derived from Todo.Info because
-// Tool.define requires z.ZodObject-typed parameters for execute() inference,
-// and zodObject(Todo.Info) returns ZodObject<any> — reaching into .shape would
-// erase field types. Tool schemas migrate to Effect Schema as a separate slice
-// per specs/effect/schema.md.
-const parameters = z.object({
-  todos: z
-    .array(
-      z.object({
-        content: z.string().describe("Brief description of the task"),
-        status: z.string().describe("Current status of the task: pending, in_progress, completed, cancelled"),
-        priority: z.string().describe("Priority level of the task: high, medium, low"),
-      }),
-    )
-    .describe("The updated todo list"),
+// Todo.Info is still a zod schema (session/todo.ts). Inline the field shape
+// here rather than referencing its `.shape` — the LLM-visible JSON Schema is
+// identical, and it removes the last zod dependency from this tool.
+const TodoItem = Schema.Struct({
+  content: Schema.String.annotate({ description: "Brief description of the task" }),
+  status: Schema.String.annotate({
+    description: "Current status of the task: pending, in_progress, completed, cancelled",
+  }),
+  priority: Schema.String.annotate({ description: "Priority level of the task: high, medium, low" }),
+})
+
+export const Parameters = Schema.Struct({
+  todos: Schema.mutable(Schema.Array(TodoItem)).annotate({ description: "The updated todo list" }),
 })
 
 type Metadata = {
   todos: Todo.Info[]
 }
 
-export const TodoWriteTool = Tool.define<typeof parameters, Metadata, Todo.Service>(
+export const TodoWriteTool = Tool.define<typeof Parameters, Metadata, Todo.Service>(
   "todowrite",
   Effect.gen(function* () {
     const todo = yield* Todo.Service
 
     return {
       description: DESCRIPTION_WRITE,
-      parameters,
-      execute: (params: z.infer<typeof parameters>, ctx: Tool.Context<Metadata>) =>
+      parameters: Parameters,
+      execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context<Metadata>) =>
         Effect.gen(function* () {
           yield* ctx.ask({
             permission: "todowrite",
@@ -55,6 +52,6 @@ export const TodoWriteTool = Tool.define<typeof parameters, Metadata, Todo.Servi
             },
           }
         }),
-    } satisfies Tool.DefWithoutID<typeof parameters, Metadata>
+    } satisfies Tool.DefWithoutID<typeof Parameters, Metadata>
   }),
 )

packages/opencode/src/tool/tool.ts

@@ -1,5 +1,4 @@
-import z from "zod"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 import type { MessageV2 } from "../session/message-v2"
 import type { Permission } from "../permission"
 import type { SessionID, MessageID } from "../session/schema"
@@ -32,29 +31,39 @@ export interface ExecuteResult<M extends Metadata = Metadata> {
   attachments?: Omit<MessageV2.FilePart, "id" | "sessionID" | "messageID">[]
 }
 
-export interface Def<Parameters extends z.ZodType = z.ZodType, M extends Metadata = Metadata> {
+export interface Def<
+  Parameters extends Schema.Decoder<unknown> = Schema.Decoder<unknown>,
+  M extends Metadata = Metadata,
+> {
   id: string
   description: string
   parameters: Parameters
-  execute(args: z.infer<Parameters>, ctx: Context): Effect.Effect<ExecuteResult<M>>
-  formatValidationError?(error: z.ZodError): string
+  execute(args: Schema.Schema.Type<Parameters>, ctx: Context): Effect.Effect<ExecuteResult<M>>
+  formatValidationError?(error: unknown): string
 }
-export type DefWithoutID<Parameters extends z.ZodType = z.ZodType, M extends Metadata = Metadata> = Omit<
-  Def<Parameters, M>,
-  "id"
->
+export type DefWithoutID<
+  Parameters extends Schema.Decoder<unknown> = Schema.Decoder<unknown>,
+  M extends Metadata = Metadata,
+> = Omit<Def<Parameters, M>, "id">
 
-export interface Info<Parameters extends z.ZodType = z.ZodType, M extends Metadata = Metadata> {
+export interface Info<
+  Parameters extends Schema.Decoder<unknown> = Schema.Decoder<unknown>,
+  M extends Metadata = Metadata,
+> {
   id: string
   init: () => Effect.Effect<DefWithoutID<Parameters, M>>
 }
 
-type Init<Parameters extends z.ZodType, M extends Metadata> =
+type Init<Parameters extends Schema.Decoder<unknown>, M extends Metadata> =
   | DefWithoutID<Parameters, M>
   | (() => Effect.Effect<DefWithoutID<Parameters, M>>)
 
 export type InferParameters<T> =
-  T extends Info<infer P, any> ? z.infer<P> : T extends Effect.Effect<Info<infer P, any>, any, any> ? z.infer<P> : never
+  T extends Info<infer P, any>
+    ? Schema.Schema.Type<P>
+    : T extends Effect.Effect<Info<infer P, any>, any, any>
+      ? Schema.Schema.Type<P>
+      : never
 export type InferMetadata<T> =
   T extends Info<any, infer M> ? M : T extends Effect.Effect<Info<any, infer M>, any, any> ? M : never
 
@@ -65,7 +74,7 @@ export type InferDef<T> =
       ? Def<P, M>
       : never
 
-function wrap<Parameters extends z.ZodType, Result extends Metadata>(
+function wrap<Parameters extends Schema.Decoder<unknown>, Result extends Metadata>(
   id: string,
   init: Init<Parameters, Result>,
   truncate: Truncate.Interface,
@@ -74,6 +83,10 @@ function wrap<Parameters extends z.ZodType, Result extends Metadata>(
   return () =>
     Effect.gen(function* () {
       const toolInfo = typeof init === "function" ? { ...(yield* init()) } : { ...init }
+      // Compile the parser closure once per tool init; `decodeUnknownEffect`
+      // allocates a new closure per call, so hoisting avoids re-closing it for
+      // every LLM tool invocation.
+      const decode = Schema.decodeUnknownEffect(toolInfo.parameters)
       const execute = toolInfo.execute
       toolInfo.execute = (args, ctx) => {
         const attrs = {
@@ -83,19 +96,17 @@ function wrap<Parameters extends z.ZodType, Result extends Metadata>(
           ...(ctx.callID ? { "tool.call_id": ctx.callID } : {}),
         }
         return Effect.gen(function* () {
-          yield* Effect.try({
-            try: () => toolInfo.parameters.parse(args),
-            catch: (error) => {
-              if (error instanceof z.ZodError && toolInfo.formatValidationError) {
-                return new Error(toolInfo.formatValidationError(error), { cause: error })
-              }
-              return new Error(
-                `The ${id} tool was called with invalid arguments: ${error}.\nPlease rewrite the input so it satisfies the expected schema.`,
-                { cause: error },
-              )
-            },
-          })
-          const result = yield* execute(args, ctx)
+          const decoded = yield* decode(args).pipe(
+            Effect.mapError((error) =>
+              toolInfo.formatValidationError
+                ? new Error(toolInfo.formatValidationError(error), { cause: error })
+                : new Error(
+                    `The ${id} tool was called with invalid arguments: ${error}.\nPlease rewrite the input so it satisfies the expected schema.`,
+                    { cause: error },
+                  ),
+            ),
+          )
+          const result = yield* execute(decoded as Schema.Schema.Type<Parameters>, ctx)
           if (result.metadata.truncated !== undefined) {
             return result
           }
@@ -116,7 +127,12 @@ function wrap<Parameters extends z.ZodType, Result extends Metadata>(
     })
 }
 
-export function define<Parameters extends z.ZodType, Result extends Metadata, R, ID extends string = string>(
+export function define<
+  Parameters extends Schema.Decoder<unknown>,
+  Result extends Metadata,
+  R,
+  ID extends string = string,
+>(
   id: ID,
   init: Effect.Effect<Init<Parameters, Result>, never, R>,
 ): Effect.Effect<Info<Parameters, Result>, never, R | Truncate.Service | Agent.Service> & { id: ID } {
@@ -131,7 +147,9 @@ export function define<Parameters extends z.ZodType, Result extends Metadata, R,
   )
 }
 
-export function init<P extends z.ZodType, M extends Metadata>(info: Info<P, M>): Effect.Effect<Def<P, M>> {
+export function init<P extends Schema.Decoder<unknown>, M extends Metadata>(
+  info: Info<P, M>,
+): Effect.Effect<Def<P, M>> {
   return Effect.gen(function* () {
     const init = yield* info.init()
     return {

packages/opencode/src/tool/webfetch.ts

@@ -1,5 +1,4 @@
-import z from "zod"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 import { HttpClient, HttpClientRequest } from "effect/unstable/http"
 import * as Tool from "./tool"
 import TurndownService from "turndown"
@@ -10,13 +9,14 @@ const MAX_RESPONSE_SIZE = 5 * 1024 * 1024 // 5MB
 const DEFAULT_TIMEOUT = 30 * 1000 // 30 seconds
 const MAX_TIMEOUT = 120 * 1000 // 2 minutes
 
-const parameters = z.object({
-  url: z.string().describe("The URL to fetch content from"),
-  format: z
-    .enum(["text", "markdown", "html"])
-    .default("markdown")
-    .describe("The format to return the content in (text, markdown, or html). Defaults to markdown."),
-  timeout: z.number().describe("Optional timeout in seconds (max 120)").optional(),
+export const Parameters = Schema.Struct({
+  url: Schema.String.annotate({ description: "The URL to fetch content from" }),
+  format: Schema.Literals(["text", "markdown", "html"])
+    .pipe(Schema.withDecodingDefaultTypeKey(Effect.succeed("markdown" as const)))
+    .annotate({
+      description: "The format to return the content in (text, markdown, or html). Defaults to markdown.",
+    }),
+  timeout: Schema.optional(Schema.Finite).annotate({ description: "Optional timeout in seconds (max 120)" }),
 })
 
 export const WebFetchTool = Tool.define(
@@ -27,8 +27,8 @@ export const WebFetchTool = Tool.define(
 
     return {
       description: DESCRIPTION,
-      parameters,
-      execute: (params: z.infer<typeof parameters>, ctx: Tool.Context) =>
+      parameters: Parameters,
+      execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) =>
         Effect.gen(function* () {
           if (!params.url.startsWith("http://") && !params.url.startsWith("https://")) {
             throw new Error("URL must start with http:// or https://")

packages/opencode/src/tool/websearch.ts

@@ -1,27 +1,28 @@
-import z from "zod"
-import { Effect } from "effect"
+import { Effect, Schema } from "effect"
 import { HttpClient } from "effect/unstable/http"
 import * as Tool from "./tool"
 import * as McpExa from "./mcp-exa"
 import DESCRIPTION from "./websearch.txt"
 
-const Parameters = z.object({
-  query: z.string().describe("Websearch query"),
-  numResults: z.number().optional().describe("Number of search results to return (default: 8)"),
-  livecrawl: z
-    .enum(["fallback", "preferred"])
-    .optional()
-    .describe(
+export const Parameters = Schema.Struct({
+  query: Schema.String.annotate({ description: "Websearch query" }),
+  numResults: Schema.Finite.pipe(Schema.withDecodingDefaultTypeKey(Effect.succeed(8))).annotate({
+    description: "Number of search results to return (default: 8)",
+  }),
+  livecrawl: Schema.Literals(["fallback", "preferred"]).pipe(
+    Schema.withDecodingDefaultTypeKey(Effect.succeed("fallback" as const)),
+  ).annotate({
+    description:
       "Live crawl mode - 'fallback': use live crawling as backup if cached content unavailable, 'preferred': prioritize live crawling (default: 'fallback')",
-    ),
-  type: z
-    .enum(["auto", "fast", "deep"])
-    .optional()
-    .describe("Search type - 'auto': balanced search (default), 'fast': quick results, 'deep': comprehensive search"),
-  contextMaxCharacters: z
-    .number()
-    .optional()
-    .describe("Maximum characters for context string optimized for LLMs (default: 10000)"),
+  }),
+  type: Schema.Literals(["auto", "fast", "deep"]).pipe(
+    Schema.withDecodingDefaultTypeKey(Effect.succeed("auto" as const)),
+  ).annotate({
+    description: "Search type - 'auto': balanced search (default), 'fast': quick results, 'deep': comprehensive search",
+  }),
+  contextMaxCharacters: Schema.optional(Schema.Finite).annotate({
+    description: "Maximum characters for context string optimized for LLMs (default: 10000)",
+  }),
 })
 
 export const WebSearchTool = Tool.define(
@@ -34,7 +35,7 @@ export const WebSearchTool = Tool.define(
         return DESCRIPTION.replace("{{year}}", new Date().getFullYear().toString())
       },
       parameters: Parameters,
-      execute: (params: z.infer<typeof Parameters>, ctx: Tool.Context) =>
+      execute: (params: Schema.Schema.Type<typeof Parameters>, ctx: Tool.Context) =>
         Effect.gen(function* () {
           yield* ctx.ask({
             permission: "websearch",
@@ -55,9 +56,9 @@ export const WebSearchTool = Tool.define(
             McpExa.SearchArgs,
             {
               query: params.query,
-              type: params.type || "auto",
-              numResults: params.numResults || 8,
-              livecrawl: params.livecrawl || "fallback",
+              type: params.type,
+              numResults: params.numResults,
+              livecrawl: params.livecrawl,
               contextMaxCharacters: params.contextMaxCharacters,
             },
             "25 seconds",

packages/opencode/src/tool/write.ts

@@ -1,4 +1,4 @@
-import z from "zod"
+import { Schema } from "effect"
 import * as path from "path"
 import { Effect } from "effect"
 import * as Tool from "./tool"
@@ -17,6 +17,13 @@ import * as Bom from "@/util/bom"
 
 const MAX_PROJECT_DIAGNOSTICS_FILES = 5
 
+export const Parameters = Schema.Struct({
+  content: Schema.String.annotate({ description: "The content to write to the file" }),
+  filePath: Schema.String.annotate({
+    description: "The absolute path to the file to write (must be absolute, not relative)",
+  }),
+})
+
 export const WriteTool = Tool.define(
   "write",
   Effect.gen(function* () {
@@ -27,10 +34,7 @@ export const WriteTool = Tool.define(
 
     return {
       description: DESCRIPTION,
-      parameters: z.object({
-        content: z.string().describe("The content to write to the file"),
-        filePath: z.string().describe("The absolute path to the file to write (must be absolute, not relative)"),
-      }),
+      parameters: Parameters,
       execute: (params: { content: string; filePath: string }, ctx: Tool.Context) =>
         Effect.gen(function* () {
           const filepath = path.isAbsolute(params.filePath)

packages/opencode/src/util/effect-zod.ts

@@ -8,6 +8,14 @@ import z from "zod"
  */
 export const ZodOverride: unique symbol = Symbol.for("effect-zod/override")
 
+/**
+ * Annotation key for attaching a `z.preprocess(...)` coercion to the derived
+ * zod schema without changing the Effect Schema's runtime behaviour. Useful
+ * for LLM-facing JSON Schemas that need to accept looser inputs (e.g. string
+ * → number) than the underlying Schema admits.
+ */
+export const ZodPreprocess: unique symbol = Symbol.for("effect-zod/preprocess")
+
 // AST nodes are immutable and frequently shared across schemas (e.g. a single
 // Schema.Class embedded in multiple parents). Memoizing by node identity
 // avoids rebuilding equivalent Zod subtrees and keeps derived children stable
@@ -49,6 +57,16 @@ function isZodType(value: unknown): value is z.ZodTypeAny {
   return typeof value === "object" && value !== null && "_zod" in value
 }
 
+/**
+ * Emit a JSON Schema for a tool/route parameter schema — derives the zod form
+ * via the walker so Effect Schema inputs flow through the same zod-openapi
+ * pipeline the LLM/SDK layer already depends on.  `io: "input"` mirrors what
+ * `session/prompt.ts` has always passed to `ai`'s `jsonSchema()` helper.
+ */
+export function toJsonSchema<S extends Schema.Top>(schema: S) {
+  return z.toJSONSchema(zod(schema), { io: "input" })
+}
+
 function walk(ast: SchemaAST.AST): z.ZodTypeAny {
   const cached = walkCache.get(ast)
   if (cached) return cached
@@ -59,8 +77,17 @@ function walk(ast: SchemaAST.AST): z.ZodTypeAny {
 
 function walkUncached(ast: SchemaAST.AST): z.ZodTypeAny {
   const override = (ast.annotations as any)?.[ZodOverride] as z.ZodTypeAny | undefined
-  if (override) return override
+  // `description` annotations layer on top of an override so callers can
+  // reuse a shared override schema (e.g. `SessionID`) and still add a
+  // per-field description on the outer wrapper.
+  const base = override ?? bodyWithChecks(ast)
+  const desc = SchemaAST.resolveDescription(ast)
+  const ref = SchemaAST.resolveIdentifier(ast)
+  const described = desc ? base.describe(desc) : base
+  return ref ? described.meta({ ref }) : described
+}
 
+function bodyWithChecks(ast: SchemaAST.AST): z.ZodTypeAny {
   // Schema.Class wraps its fields in a Declaration AST plus an encoding that
   // constructs the class instance. For the Zod derivation we want the plain
   // field shape (the decoded/consumer view), not the class instance — so
@@ -68,17 +95,18 @@ function walkUncached(ast: SchemaAST.AST): z.ZodTypeAny {
   // Schema.decodeTo / Schema.transform attach encoding to non-Declaration
   // nodes, where we do apply the transform.
   //
-  // Schema.withDecodingDefault also attaches encoding, but we want `.default(v)`
-  // on the inner Zod rather than a transform wrapper — so optional ASTs whose
-  // encoding resolves a default from Option.none() route through body()/opt().
+  // Schema.withDecodingDefault and Schema.withDecodingDefaultTypeKey both
+  // attach encodings. For JSON Schema we want those as plain `.default(v)`
+  // annotations rather than transform wrappers, so ASTs whose encoding
+  // resolves a default from Option.none() route through body()/opt().
   const hasEncoding = ast.encoding?.length && ast._tag !== "Declaration"
-  const hasTransform = hasEncoding && !(SchemaAST.isOptional(ast) && extractDefault(ast) !== undefined)
-  const base = hasTransform ? encoded(ast) : body(ast)
+  const fallback = hasEncoding ? extractDefault(ast) : undefined
+  const hasTransform = hasEncoding && fallback === undefined
+  const base = hasTransform ? encoded(ast) : body(ast, fallback)
   const checked = ast.checks?.length ? applyChecks(base, ast.checks, ast) : base
-  const desc = SchemaAST.resolveDescription(ast)
-  const ref = SchemaAST.resolveIdentifier(ast)
-  const described = desc ? checked.describe(desc) : checked
-  return ref ? described.meta({ ref }) : described
+  const defaulted = fallback !== undefined && !SchemaAST.isOptional(ast) ? checked.default(fallback.value) : checked
+  const preprocess = (ast.annotations as { [ZodPreprocess]?: (val: unknown) => unknown } | undefined)?.[ZodPreprocess]
+  return preprocess ? z.preprocess(preprocess, defaulted) : defaulted
 }
 
 // Walk the encoded side and apply each link's decode to produce the decoded
@@ -212,8 +240,8 @@ function issueMessage(issue: any): string | undefined {
   return undefined
 }
 
-function body(ast: SchemaAST.AST): z.ZodTypeAny {
-  if (SchemaAST.isOptional(ast)) return opt(ast)
+function body(ast: SchemaAST.AST, fallback?: { value: unknown }): z.ZodTypeAny {
+  if (SchemaAST.isOptional(ast)) return opt(ast, fallback)
 
   switch (ast._tag) {
     case "String":
@@ -246,7 +274,7 @@ function body(ast: SchemaAST.AST): z.ZodTypeAny {
   }
 }
 
-function opt(ast: SchemaAST.AST): z.ZodTypeAny {
+function opt(ast: SchemaAST.AST, fallback = extractDefault(ast)): z.ZodTypeAny {
   if (ast._tag !== "Union") return fail(ast)
   const items = ast.types.filter((item) => item._tag !== "Undefined")
   const inner =
@@ -258,7 +286,6 @@ function opt(ast: SchemaAST.AST): z.ZodTypeAny {
   // Schema.withDecodingDefault attaches an encoding `Link` whose transformation
   // decode Getter resolves `Option.none()` to `Option.some(default)`.  Invoke
   // it to extract the default and emit `.default(...)` instead of `.optional()`.
-  const fallback = extractDefault(ast)
   if (fallback !== undefined) return inner.default(fallback.value)
   return inner.optional()
 }

packages/opencode/src/util/schema.ts

@@ -1,5 +1,43 @@
 import { Schema } from "effect"
 
+/**
+ * Integer greater than zero.
+ */
+export const PositiveInt = Schema.Int.check(Schema.isGreaterThan(0))
+
+/**
+ * Integer greater than or equal to zero.
+ */
+export const NonNegativeInt = Schema.Int.check(Schema.isGreaterThanOrEqualTo(0))
+
+/**
+ * Strip `readonly` from a nested type. Stand-in for `effect`'s `Types.DeepMutable`
+ * until `effect:core/x228my` ("Types.DeepMutable widens unknown to `{}`") lands.
+ *
+ * The upstream version falls through `unknown` into `{ -readonly [K in keyof T]: ... }`
+ * where `keyof unknown = never`, so `unknown` collapses to `{}`. This local
+ * version gates the object branch on `extends object` (which `unknown` does
+ * not) so `unknown` passes through untouched.
+ *
+ * Primitive bailout matches upstream — without it, branded strings like
+ * `string & Brand<"SessionID">` fall into the object branch and get their
+ * prototype methods walked.
+ *
+ * Tuple branch preserves readonly tuples (e.g. `ConfigPlugin.Spec`'s
+ * `readonly [string, Options]`); the general array branch would otherwise
+ * widen them to unbounded arrays.
+ */
+// eslint-disable-next-line @typescript-eslint/ban-types
+export type DeepMutable<T> = T extends string | number | boolean | bigint | symbol | Function
+  ? T
+  : T extends readonly [unknown, ...unknown[]]
+    ? { -readonly [K in keyof T]: DeepMutable<T[K]> }
+    : T extends readonly (infer U)[]
+      ? DeepMutable<U>[]
+      : T extends object
+        ? { -readonly [K in keyof T]: DeepMutable<T[K]> }
+        : T
+
 /**
  * Attach static methods to a schema object. Designed to be used with `.pipe()`:
  *
@@ -16,13 +54,16 @@ export const withStatics =
   (schema: S): S & M =>
     Object.assign(schema, methods(schema))
 
-declare const NewtypeBrand: unique symbol
-type NewtypeBrand<Tag extends string> = { readonly [NewtypeBrand]: Tag }
-
 /**
  * Nominal wrapper for scalar types. The class itself is a valid schema —
  * pass it directly to `Schema.decode`, `Schema.decodeEffect`, etc.
  *
+ * Overrides `~type.make` on the derived `Schema.Opaque` so `Schema.Schema.Type`
+ * of a field using this newtype resolves to `Self` rather than the underlying
+ * branded phantom. Without that override, passing a class instance to code
+ * typed against `Schema.Schema.Type<FieldSchema>` would require a cast even
+ * though the values are structurally equivalent at runtime.
+ *
  * @example
  *   class QuestionID extends Newtype<QuestionID>()("QuestionID", Schema.String) {
  *     static make(id: string): QuestionID {
@@ -34,10 +75,8 @@ type NewtypeBrand<Tag extends string> = { readonly [NewtypeBrand]: Tag }
  */
 export function Newtype<Self>() {
   return <const Tag extends string, S extends Schema.Top>(tag: Tag, schema: S) => {
-    type Branded = NewtypeBrand<Tag>
-
     abstract class Base {
-      declare readonly [NewtypeBrand]: Tag
+      declare readonly _newtype: Tag
 
       static make(value: Schema.Schema.Type<S>): Self {
         return value as unknown as Self
@@ -46,8 +85,10 @@ export function Newtype<Self>() {
 
     Object.setPrototypeOf(Base, schema)
 
-    return Base as unknown as (abstract new (_: never) => Branded) & {
+    return Base as unknown as (abstract new (_: never) => { readonly _newtype: Tag }) & {
       readonly make: (value: Schema.Schema.Type<S>) => Self
-    } & Omit<Schema.Opaque<Self, S, {}>, "make">
+    } & Omit<Schema.Opaque<Self, S, {}>, "make" | "~type.make"> & {
+        readonly "~type.make": Self
+      }
   }
 }

packages/opencode/src/worktree/index.ts

@@ -13,7 +13,7 @@ import { errorMessage } from "../util/error"
 import { BusEvent } from "@/bus/bus-event"
 import { GlobalBus } from "@/bus/global"
 import { Git } from "@/git"
-import { Effect, Layer, Path, Scope, Context, Stream } from "effect"
+import { Effect, Layer, Path, Schema, Scope, Context, Stream } from "effect"
 import { ChildProcess, ChildProcessSpawner } from "effect/unstable/process"
 import { NodePath } from "@effect/platform-node"
 import { AppFileSystem } from "@opencode-ai/shared/filesystem"
@@ -26,15 +26,15 @@ const log = Log.create({ service: "worktree" })
 export const Event = {
   Ready: BusEvent.define(
     "worktree.ready",
-    z.object({
-      name: z.string(),
-      branch: z.string(),
+    Schema.Struct({
+      name: Schema.String,
+      branch: Schema.String,
     }),
   ),
   Failed: BusEvent.define(
     "worktree.failed",
-    z.object({
-      message: z.string(),
+    Schema.Struct({
+      message: Schema.String,
     }),
   ),
 }

packages/opencode/test/bus/bus-effect.test.ts

@@ -1,6 +1,5 @@
 import { describe, expect } from "bun:test"
-import { Deferred, Effect, Layer, Stream } from "effect"
-import z from "zod"
+import { Deferred, Effect, Layer, Schema, Stream } from "effect"
 import { Bus } from "../../src/bus"
 import { BusEvent } from "../../src/bus/bus-event"
 import { Instance } from "../../src/project/instance"
@@ -9,8 +8,8 @@ import { provideInstance, provideTmpdirInstance, tmpdirScoped } from "../fixture
 import { testEffect } from "../lib/effect"
 
 const TestEvent = {
-  Ping: BusEvent.define("test.effect.ping", z.object({ value: z.number() })),
-  Pong: BusEvent.define("test.effect.pong", z.object({ message: z.string() })),
+  Ping: BusEvent.define("test.effect.ping", Schema.Struct({ value: Schema.Number })),
+  Pong: BusEvent.define("test.effect.pong", Schema.Struct({ message: Schema.String })),
 }
 
 const node = CrossSpawnSpawner.defaultLayer

packages/opencode/test/bus/bus-integration.test.ts

@@ -1,11 +1,11 @@
 import { afterEach, describe, expect, test } from "bun:test"
-import z from "zod"
+import { Schema } from "effect"
 import { Bus } from "../../src/bus"
 import { BusEvent } from "../../src/bus/bus-event"
 import { Instance } from "../../src/project/instance"
 import { tmpdir } from "../fixture/fixture"
 
-const TestEvent = BusEvent.define("test.integration", z.object({ value: z.number() }))
+const TestEvent = BusEvent.define("test.integration", Schema.Struct({ value: Schema.Number }))
 
 function withInstance(directory: string, fn: () => Promise<void>) {
   return Instance.provide({ directory, fn })
@@ -42,7 +42,7 @@ describe("Bus integration: acquireRelease subscriber pattern", () => {
     await using tmp = await tmpdir()
     const received: Array<{ type: string; value?: number }> = []
 
-    const OtherEvent = BusEvent.define("test.other", z.object({ value: z.number() }))
+    const OtherEvent = BusEvent.define("test.other", Schema.Struct({ value: Schema.Number }))
 
     await withInstance(tmp.path, async () => {
       Bus.subscribeAll((evt) => {

packages/opencode/test/bus/bus.test.ts

@@ -1,13 +1,13 @@
 import { afterEach, describe, expect, test } from "bun:test"
-import z from "zod"
+import { Schema } from "effect"
 import { Bus } from "../../src/bus"
 import { BusEvent } from "../../src/bus/bus-event"
 import { Instance } from "../../src/project/instance"
 import { tmpdir } from "../fixture/fixture"
 
 const TestEvent = {
-  Ping: BusEvent.define("test.ping", z.object({ value: z.number() })),
-  Pong: BusEvent.define("test.pong", z.object({ message: z.string() })),
+  Ping: BusEvent.define("test.ping", Schema.Struct({ value: Schema.Number })),
+  Pong: BusEvent.define("test.pong", Schema.Struct({ message: Schema.String })),
 }
 
 function withInstance(directory: string, fn: () => Promise<void>) {

packages/opencode/test/session/session.test.ts

@@ -111,9 +111,12 @@ describe("step-finish token propagation via Bus event", () => {
             mode: "",
           } as unknown as MessageV2.Info)
 
+          // Bus subscribers receive readonly Schema.Type payloads; `MessageV2.Part`
+          // is the mutable domain type. Cast bridges the two — safe because the
+          // test only reads the value afterwards.
           let received: MessageV2.Part | undefined
           const unsub = Bus.subscribe(MessageV2.Event.PartUpdated, (event) => {
-            received = event.properties.part
+            received = event.properties.part as MessageV2.Part
           })
 
           const tokens = {

packages/opencode/test/sync/index.test.ts

@@ -1,6 +1,6 @@
 import { describe, test, expect, beforeEach, afterEach, afterAll } from "bun:test"
 import { tmpdir } from "../fixture/fixture"
-import z from "zod"
+import { Schema } from "effect"
 import { Bus } from "../../src/bus"
 import { Instance } from "../../src/project/instance"
 import { SyncEvent } from "../../src/sync"
@@ -43,13 +43,13 @@ describe("SyncEvent", () => {
       type: "item.created",
       version: 1,
       aggregate: "id",
-      schema: z.object({ id: z.string(), name: z.string() }),
+      schema: Schema.Struct({ id: Schema.String, name: Schema.String }),
     })
     const Sent = SyncEvent.define({
       type: "item.sent",
       version: 1,
       aggregate: "item_id",
-      schema: z.object({ item_id: z.string(), to: z.string() }),
+      schema: Schema.Struct({ item_id: Schema.String, to: Schema.String }),
     })
 
     SyncEvent.init({

packages/opencode/test/tool/__snapshots__/parameters.test.ts.snap

@@ -0,0 +1,498 @@
+// Bun Snapshot v1, https://bun.sh/docs/test/snapshots
+
+exports[`tool parameters JSON Schema (wire shape) apply_patch 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "patchText": {
+      "description": "The full patch text that describes all changes to be made",
+      "type": "string",
+    },
+  },
+  "required": [
+    "patchText",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) bash 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "command": {
+      "description": "The command to execute",
+      "type": "string",
+    },
+    "description": {
+      "description": 
+"Clear, concise description of what this command does in 5-10 words. Examples:
+Input: ls
+Output: Lists files in current directory
+
+Input: git status
+Output: Shows working tree status
+
+Input: npm install
+Output: Installs package dependencies
+
+Input: mkdir foo
+Output: Creates directory 'foo'"
+,
+      "type": "string",
+    },
+    "timeout": {
+      "description": "Optional timeout in milliseconds",
+      "type": "number",
+    },
+    "workdir": {
+      "description": "The working directory to run the command in. Defaults to the current directory. Use this instead of 'cd' commands.",
+      "type": "string",
+    },
+  },
+  "required": [
+    "command",
+    "description",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) codesearch 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "query": {
+      "description": "Search query to find relevant context for APIs, Libraries, and SDKs. For example, 'React useState hook examples', 'Python pandas dataframe filtering', 'Express.js middleware', 'Next js partial prerendering configuration'",
+      "type": "string",
+    },
+    "tokensNum": {
+      "default": 5000,
+      "description": "Number of tokens to return (1000-50000). Default is 5000 tokens. Adjust this value based on how much context you need - use lower values for focused queries and higher values for comprehensive documentation.",
+      "maximum": 50000,
+      "minimum": 1000,
+      "type": "number",
+    },
+  },
+  "required": [
+    "query",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) edit 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "filePath": {
+      "description": "The absolute path to the file to modify",
+      "type": "string",
+    },
+    "newString": {
+      "description": "The text to replace it with (must be different from oldString)",
+      "type": "string",
+    },
+    "oldString": {
+      "description": "The text to replace",
+      "type": "string",
+    },
+    "replaceAll": {
+      "description": "Replace all occurrences of oldString (default false)",
+      "type": "boolean",
+    },
+  },
+  "required": [
+    "filePath",
+    "oldString",
+    "newString",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) glob 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "path": {
+      "description": "The directory to search in. If not specified, the current working directory will be used. IMPORTANT: Omit this field to use the default directory. DO NOT enter "undefined" or "null" - simply omit it for the default behavior. Must be a valid directory path if provided.",
+      "type": "string",
+    },
+    "pattern": {
+      "description": "The glob pattern to match files against",
+      "type": "string",
+    },
+  },
+  "required": [
+    "pattern",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) grep 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "include": {
+      "description": "File pattern to include in the search (e.g. "*.js", "*.{ts,tsx}")",
+      "type": "string",
+    },
+    "path": {
+      "description": "The directory to search in. Defaults to the current working directory.",
+      "type": "string",
+    },
+    "pattern": {
+      "description": "The regex pattern to search for in file contents",
+      "type": "string",
+    },
+  },
+  "required": [
+    "pattern",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) invalid 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "error": {
+      "type": "string",
+    },
+    "tool": {
+      "type": "string",
+    },
+  },
+  "required": [
+    "tool",
+    "error",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) lsp 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "character": {
+      "description": "The character offset (1-based, as shown in editors)",
+      "maximum": 9007199254740991,
+      "minimum": 1,
+      "type": "integer",
+    },
+    "filePath": {
+      "description": "The absolute or relative path to the file",
+      "type": "string",
+    },
+    "line": {
+      "description": "The line number (1-based, as shown in editors)",
+      "maximum": 9007199254740991,
+      "minimum": 1,
+      "type": "integer",
+    },
+    "operation": {
+      "description": "The LSP operation to perform",
+      "enum": [
+        "goToDefinition",
+        "findReferences",
+        "hover",
+        "documentSymbol",
+        "workspaceSymbol",
+        "goToImplementation",
+        "prepareCallHierarchy",
+        "incomingCalls",
+        "outgoingCalls",
+      ],
+      "type": "string",
+    },
+  },
+  "required": [
+    "operation",
+    "filePath",
+    "line",
+    "character",
+  ],
+  "type": "object",
+}
+`;
+
+
+exports[`tool parameters JSON Schema (wire shape) plan 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {},
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) question 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "questions": {
+      "description": "Questions to ask",
+      "items": {
+        "properties": {
+          "header": {
+            "description": "Very short label (max 30 chars)",
+            "type": "string",
+          },
+          "multiple": {
+            "description": "Allow selecting multiple choices",
+            "type": "boolean",
+          },
+          "options": {
+            "description": "Available choices",
+            "items": {
+              "properties": {
+                "description": {
+                  "description": "Explanation of choice",
+                  "type": "string",
+                },
+                "label": {
+                  "description": "Display text (1-5 words, concise)",
+                  "type": "string",
+                },
+              },
+              "ref": "QuestionOption",
+              "required": [
+                "label",
+                "description",
+              ],
+              "type": "object",
+            },
+            "type": "array",
+          },
+          "question": {
+            "description": "Complete question",
+            "type": "string",
+          },
+        },
+        "ref": "QuestionPrompt",
+        "required": [
+          "question",
+          "header",
+          "options",
+        ],
+        "type": "object",
+      },
+      "type": "array",
+    },
+  },
+  "required": [
+    "questions",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) read 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "filePath": {
+      "description": "The absolute path to the file or directory to read",
+      "type": "string",
+    },
+    "limit": {
+      "description": "The maximum number of lines to read (defaults to 2000)",
+      "type": "number",
+    },
+    "offset": {
+      "description": "The line number to start reading from (1-indexed)",
+      "type": "number",
+    },
+  },
+  "required": [
+    "filePath",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) skill 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "name": {
+      "description": "The name of the skill from available_skills",
+      "type": "string",
+    },
+  },
+  "required": [
+    "name",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) task 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "command": {
+      "description": "The command that triggered this task",
+      "type": "string",
+    },
+    "description": {
+      "description": "A short (3-5 words) description of the task",
+      "type": "string",
+    },
+    "prompt": {
+      "description": "The task for the agent to perform",
+      "type": "string",
+    },
+    "subagent_type": {
+      "description": "The type of specialized agent to use for this task",
+      "type": "string",
+    },
+    "task_id": {
+      "description": "This should only be set if you mean to resume a previous task (you can pass a prior task_id and the task will continue the same subagent session as before instead of creating a fresh one)",
+      "type": "string",
+    },
+  },
+  "required": [
+    "description",
+    "prompt",
+    "subagent_type",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) todo 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "todos": {
+      "description": "The updated todo list",
+      "items": {
+        "properties": {
+          "content": {
+            "description": "Brief description of the task",
+            "type": "string",
+          },
+          "priority": {
+            "description": "Priority level of the task: high, medium, low",
+            "type": "string",
+          },
+          "status": {
+            "description": "Current status of the task: pending, in_progress, completed, cancelled",
+            "type": "string",
+          },
+        },
+        "required": [
+          "content",
+          "status",
+          "priority",
+        ],
+        "type": "object",
+      },
+      "type": "array",
+    },
+  },
+  "required": [
+    "todos",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) webfetch 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "format": {
+      "default": "markdown",
+      "description": "The format to return the content in (text, markdown, or html). Defaults to markdown.",
+      "enum": [
+        "text",
+        "markdown",
+        "html",
+      ],
+      "type": "string",
+    },
+    "timeout": {
+      "description": "Optional timeout in seconds (max 120)",
+      "type": "number",
+    },
+    "url": {
+      "description": "The URL to fetch content from",
+      "type": "string",
+    },
+  },
+  "required": [
+    "url",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) websearch 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "contextMaxCharacters": {
+      "description": "Maximum characters for context string optimized for LLMs (default: 10000)",
+      "type": "number",
+    },
+    "livecrawl": {
+      "default": "fallback",
+      "description": "Live crawl mode - 'fallback': use live crawling as backup if cached content unavailable, 'preferred': prioritize live crawling (default: 'fallback')",
+      "enum": [
+        "fallback",
+        "preferred",
+      ],
+      "type": "string",
+    },
+    "numResults": {
+      "default": 8,
+      "description": "Number of search results to return (default: 8)",
+      "type": "number",
+    },
+    "query": {
+      "description": "Websearch query",
+      "type": "string",
+    },
+    "type": {
+      "default": "auto",
+      "description": "Search type - 'auto': balanced search (default), 'fast': quick results, 'deep': comprehensive search",
+      "enum": [
+        "auto",
+        "fast",
+        "deep",
+      ],
+      "type": "string",
+    },
+  },
+  "required": [
+    "query",
+  ],
+  "type": "object",
+}
+`;
+
+exports[`tool parameters JSON Schema (wire shape) write 1`] = `
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "content": {
+      "description": "The content to write to the file",
+      "type": "string",
+    },
+    "filePath": {
+      "description": "The absolute path to the file to write (must be absolute, not relative)",
+      "type": "string",
+    },
+  },
+  "required": [
+    "content",
+    "filePath",
+  ],
+  "type": "object",
+}
+`;

packages/opencode/test/tool/parameters.test.ts

@@ -0,0 +1,304 @@
+import { describe, expect, test } from "bun:test"
+import { Result, Schema } from "effect"
+import { toJsonSchema } from "../../src/util/effect-zod"
+
+// Each tool exports its parameters schema at module scope so this test can
+// import them without running the tool's Effect-based init. The JSON Schema
+// snapshot captures what the LLM sees; the parse assertions pin down the
+// accepts/rejects contract. `toJsonSchema` is the same helper `session/
+// prompt.ts` uses to emit tool schemas to the LLM, so the snapshots stay
+// byte-identical regardless of whether a tool has migrated from zod to Schema.
+
+import { Parameters as ApplyPatch } from "../../src/tool/apply_patch"
+import { Parameters as Bash } from "../../src/tool/bash"
+import { Parameters as CodeSearch } from "../../src/tool/codesearch"
+import { Parameters as Edit } from "../../src/tool/edit"
+import { Parameters as Glob } from "../../src/tool/glob"
+import { Parameters as Grep } from "../../src/tool/grep"
+import { Parameters as Invalid } from "../../src/tool/invalid"
+import { Parameters as Lsp } from "../../src/tool/lsp"
+import { Parameters as Plan } from "../../src/tool/plan"
+import { Parameters as Question } from "../../src/tool/question"
+import { Parameters as Read } from "../../src/tool/read"
+import { Parameters as Skill } from "../../src/tool/skill"
+import { Parameters as Task } from "../../src/tool/task"
+import { Parameters as Todo } from "../../src/tool/todo"
+import { Parameters as WebFetch } from "../../src/tool/webfetch"
+import { Parameters as WebSearch } from "../../src/tool/websearch"
+import { Parameters as Write } from "../../src/tool/write"
+
+const parse = <S extends Schema.Decoder<unknown>>(schema: S, input: unknown): S["Type"] =>
+  Schema.decodeUnknownSync(schema)(input)
+
+const accepts = (schema: Schema.Decoder<unknown>, input: unknown): boolean =>
+  Result.isSuccess(Schema.decodeUnknownResult(schema)(input))
+
+const toNativeJsonSchema = <S extends Schema.Decoder<unknown>>(schema: S) =>
+  Schema.toStandardJSONSchemaV1(schema)["~standard"].jsonSchema.input({ target: "draft-2020-12" })
+
+describe("tool parameters", () => {
+  describe("JSON Schema (wire shape)", () => {
+    test("apply_patch", () => expect(toJsonSchema(ApplyPatch)).toMatchSnapshot())
+    test("bash", () => expect(toJsonSchema(Bash)).toMatchSnapshot())
+    test("codesearch", () => expect(toJsonSchema(CodeSearch)).toMatchSnapshot())
+    test("edit", () => expect(toJsonSchema(Edit)).toMatchSnapshot())
+    test("glob", () => expect(toJsonSchema(Glob)).toMatchSnapshot())
+    test("grep", () => expect(toJsonSchema(Grep)).toMatchSnapshot())
+    test("invalid", () => expect(toJsonSchema(Invalid)).toMatchSnapshot())
+    test("lsp", () => expect(toJsonSchema(Lsp)).toMatchSnapshot())
+    test("plan", () => expect(toJsonSchema(Plan)).toMatchSnapshot())
+    test("question", () => expect(toJsonSchema(Question)).toMatchSnapshot())
+    test("read", () => expect(toJsonSchema(Read)).toMatchSnapshot())
+    test("skill", () => expect(toJsonSchema(Skill)).toMatchSnapshot())
+    test("task", () => expect(toJsonSchema(Task)).toMatchSnapshot())
+    test("todo", () => expect(toJsonSchema(Todo)).toMatchSnapshot())
+    test("webfetch", () => expect(toJsonSchema(WebFetch)).toMatchSnapshot())
+    test("websearch", () => expect(toJsonSchema(WebSearch)).toMatchSnapshot())
+    test("write", () => expect(toJsonSchema(Write)).toMatchSnapshot())
+  })
+
+  describe("native JSON Schema (experimental tool route)", () => {
+    test("codesearch uses a plain finite number", () => {
+      const native = toNativeJsonSchema(CodeSearch) as any
+      expect(native.properties.tokensNum).toEqual({
+        type: "number",
+        allOf: [{ minimum: 1000 }, { maximum: 50000 }],
+      })
+    })
+
+    test("webfetch format stays a string enum", () => {
+      const native = toNativeJsonSchema(WebFetch) as any
+      expect(native.properties.format).toEqual({
+        type: "string",
+        enum: ["text", "markdown", "html"],
+      })
+    })
+
+    test("websearch defaulted fields stay non-nullable", () => {
+      const native = toNativeJsonSchema(WebSearch) as any
+      expect(native.properties.numResults).toEqual({
+        type: "number",
+      })
+      expect(native.properties.livecrawl).toEqual({
+        type: "string",
+        enum: ["fallback", "preferred"],
+      })
+      expect(native.properties.type).toEqual({
+        type: "string",
+        enum: ["auto", "fast", "deep"],
+      })
+    })
+  })
+
+  describe("apply_patch", () => {
+    test("accepts patchText", () => {
+      expect(parse(ApplyPatch, { patchText: "*** Begin Patch\n*** End Patch" })).toEqual({
+        patchText: "*** Begin Patch\n*** End Patch",
+      })
+    })
+    test("rejects missing patchText", () => {
+      expect(accepts(ApplyPatch, {})).toBe(false)
+    })
+    test("rejects non-string patchText", () => {
+      expect(accepts(ApplyPatch, { patchText: 123 })).toBe(false)
+    })
+  })
+
+  describe("bash", () => {
+    test("accepts minimum: command + description", () => {
+      expect(parse(Bash, { command: "ls", description: "list" })).toEqual({ command: "ls", description: "list" })
+    })
+    test("accepts optional timeout + workdir", () => {
+      const parsed = parse(Bash, { command: "ls", description: "list", timeout: 5000, workdir: "/tmp" })
+      expect(parsed.timeout).toBe(5000)
+      expect(parsed.workdir).toBe("/tmp")
+    })
+    test("rejects missing description (required by zod)", () => {
+      expect(accepts(Bash, { command: "ls" })).toBe(false)
+    })
+    test("rejects missing command", () => {
+      expect(accepts(Bash, { description: "list" })).toBe(false)
+    })
+  })
+
+  describe("codesearch", () => {
+    test("accepts query; tokensNum defaults to 5000", () => {
+      expect(parse(CodeSearch, { query: "hooks" })).toEqual({ query: "hooks", tokensNum: 5000 })
+    })
+    test("accepts override tokensNum", () => {
+      expect(parse(CodeSearch, { query: "hooks", tokensNum: 10000 }).tokensNum).toBe(10000)
+    })
+    test("rejects tokensNum under 1000", () => {
+      expect(accepts(CodeSearch, { query: "x", tokensNum: 500 })).toBe(false)
+    })
+    test("rejects tokensNum over 50000", () => {
+      expect(accepts(CodeSearch, { query: "x", tokensNum: 60000 })).toBe(false)
+    })
+  })
+
+  describe("edit", () => {
+    test("accepts all four fields", () => {
+      expect(parse(Edit, { filePath: "/a", oldString: "x", newString: "y", replaceAll: true })).toEqual({
+        filePath: "/a",
+        oldString: "x",
+        newString: "y",
+        replaceAll: true,
+      })
+    })
+    test("replaceAll is optional", () => {
+      const parsed = parse(Edit, { filePath: "/a", oldString: "x", newString: "y" })
+      expect(parsed.replaceAll).toBeUndefined()
+    })
+    test("rejects missing filePath", () => {
+      expect(accepts(Edit, { oldString: "x", newString: "y" })).toBe(false)
+    })
+  })
+
+  describe("glob", () => {
+    test("accepts pattern-only", () => {
+      expect(parse(Glob, { pattern: "**/*.ts" })).toEqual({ pattern: "**/*.ts" })
+    })
+    test("accepts optional path", () => {
+      expect(parse(Glob, { pattern: "**/*.ts", path: "/tmp" }).path).toBe("/tmp")
+    })
+    test("rejects missing pattern", () => {
+      expect(accepts(Glob, {})).toBe(false)
+    })
+  })
+
+  describe("grep", () => {
+    test("accepts pattern-only", () => {
+      expect(parse(Grep, { pattern: "TODO" })).toEqual({ pattern: "TODO" })
+    })
+    test("accepts optional path + include", () => {
+      const parsed = parse(Grep, { pattern: "TODO", path: "/tmp", include: "*.ts" })
+      expect(parsed.path).toBe("/tmp")
+      expect(parsed.include).toBe("*.ts")
+    })
+    test("rejects missing pattern", () => {
+      expect(accepts(Grep, {})).toBe(false)
+    })
+  })
+
+  describe("invalid", () => {
+    test("accepts tool + error", () => {
+      expect(parse(Invalid, { tool: "foo", error: "bar" })).toEqual({ tool: "foo", error: "bar" })
+    })
+    test("rejects missing fields", () => {
+      expect(accepts(Invalid, { tool: "foo" })).toBe(false)
+      expect(accepts(Invalid, { error: "bar" })).toBe(false)
+    })
+  })
+
+  describe("lsp", () => {
+    test("accepts all fields", () => {
+      const parsed = parse(Lsp, { operation: "hover", filePath: "/a.ts", line: 1, character: 1 })
+      expect(parsed.operation).toBe("hover")
+    })
+    test("rejects line < 1", () => {
+      expect(accepts(Lsp, { operation: "hover", filePath: "/a.ts", line: 0, character: 1 })).toBe(false)
+    })
+    test("rejects character < 1", () => {
+      expect(accepts(Lsp, { operation: "hover", filePath: "/a.ts", line: 1, character: 0 })).toBe(false)
+    })
+    test("rejects unknown operation", () => {
+      expect(accepts(Lsp, { operation: "bogus", filePath: "/a.ts", line: 1, character: 1 })).toBe(false)
+    })
+  })
+
+  describe("plan", () => {
+    test("accepts empty object", () => {
+      expect(parse(Plan, {})).toEqual({})
+    })
+  })
+
+  describe("question", () => {
+    test("accepts questions array", () => {
+      const parsed = parse(Question, {
+        questions: [
+          {
+            question: "pick one",
+            header: "Header",
+            custom: false,
+            options: [{ label: "a", description: "desc" }],
+          },
+        ],
+      })
+      expect(parsed.questions.length).toBe(1)
+    })
+    test("rejects missing questions", () => {
+      expect(accepts(Question, {})).toBe(false)
+    })
+  })
+
+  describe("read", () => {
+    test("accepts filePath-only", () => {
+      expect(parse(Read, { filePath: "/a" }).filePath).toBe("/a")
+    })
+    test("accepts optional offset + limit", () => {
+      const parsed = parse(Read, { filePath: "/a", offset: 10, limit: 100 })
+      expect(parsed.offset).toBe(10)
+      expect(parsed.limit).toBe(100)
+    })
+  })
+
+  describe("skill", () => {
+    test("accepts name", () => {
+      expect(parse(Skill, { name: "foo" }).name).toBe("foo")
+    })
+    test("rejects missing name", () => {
+      expect(accepts(Skill, {})).toBe(false)
+    })
+  })
+
+  describe("task", () => {
+    test("accepts description + prompt + subagent_type", () => {
+      const parsed = parse(Task, { description: "d", prompt: "p", subagent_type: "general" })
+      expect(parsed.subagent_type).toBe("general")
+    })
+    test("rejects missing prompt", () => {
+      expect(accepts(Task, { description: "d", subagent_type: "general" })).toBe(false)
+    })
+  })
+
+  describe("todo", () => {
+    test("accepts todos array", () => {
+      const parsed = parse(Todo, {
+        todos: [{ id: "t1", content: "do x", status: "pending", priority: "medium" }],
+      })
+      expect(parsed.todos.length).toBe(1)
+    })
+    test("rejects missing todos", () => {
+      expect(accepts(Todo, {})).toBe(false)
+    })
+  })
+
+  describe("webfetch", () => {
+    test("accepts url-only", () => {
+      expect(parse(WebFetch, { url: "https://example.com" })).toEqual({
+        url: "https://example.com",
+        format: "markdown",
+      })
+    })
+  })
+
+  describe("websearch", () => {
+    test("accepts query", () => {
+      expect(parse(WebSearch, { query: "opencode" })).toEqual({
+        query: "opencode",
+        numResults: 8,
+        livecrawl: "fallback",
+        type: "auto",
+      })
+    })
+  })
+
+  describe("write", () => {
+    test("accepts content + filePath", () => {
+      expect(parse(Write, { content: "hi", filePath: "/a" })).toEqual({ content: "hi", filePath: "/a" })
+    })
+    test("rejects missing filePath", () => {
+      expect(accepts(Write, { content: "hi" })).toBe(false)
+    })
+  })
+})

packages/opencode/test/tool/tool-define.test.ts

@@ -1,13 +1,13 @@
 import { describe, test, expect } from "bun:test"
-import { Effect, Layer, ManagedRuntime } from "effect"
-import z from "zod"
+import { Effect, Layer, ManagedRuntime, Schema } from "effect"
 import { Agent } from "../../src/agent/agent"
+import { MessageID, SessionID } from "../../src/session/schema"
 import { Tool } from "../../src/tool"
 import { Truncate } from "../../src/tool"
 
 const runtime = ManagedRuntime.make(Layer.mergeAll(Truncate.defaultLayer, Agent.defaultLayer))
 
-const params = z.object({ input: z.string() })
+const params = Schema.Struct({ input: Schema.String })
 
 function makeTool(id: string, executeFn?: () => void) {
   return {
@@ -56,4 +56,44 @@ describe("Tool.define", () => {
 
     expect(first).not.toBe(second)
   })
+
+  test("execute receives decoded parameters", async () => {
+    const parameters = Schema.Struct({
+      count: Schema.NumberFromString.pipe(Schema.optional, Schema.withDecodingDefaultType(Effect.succeed(5))),
+    })
+    const calls: Array<Schema.Schema.Type<typeof parameters>> = []
+    const info = await runtime.runPromise(
+      Tool.define(
+        "test-decoded",
+        Effect.succeed({
+          description: "test tool",
+          parameters,
+          execute(args: Schema.Schema.Type<typeof parameters>) {
+            calls.push(args)
+            return Effect.succeed({ title: "test", output: "ok", metadata: { truncated: false } })
+          },
+        }),
+      ),
+    )
+    const ctx: Tool.Context = {
+      sessionID: SessionID.descending(),
+      messageID: MessageID.ascending(),
+      agent: "build",
+      abort: new AbortController().signal,
+      messages: [],
+      metadata() {
+        return Effect.void
+      },
+      ask() {
+        return Effect.void
+      },
+    }
+    const tool = await Effect.runPromise(info.init())
+    const execute = tool.execute as unknown as (args: unknown, ctx: Tool.Context) => ReturnType<typeof tool.execute>
+
+    await Effect.runPromise(execute({}, ctx))
+    await Effect.runPromise(execute({ count: "7" }, ctx))
+
+    expect(calls).toEqual([{ count: 5 }, { count: 7 }])
+  })
 })

packages/opencode/test/util/effect-zod.test.ts

@@ -2,7 +2,7 @@ import { describe, expect, test } from "bun:test"
 import { Effect, Schema, SchemaGetter } from "effect"
 import z from "zod"
 
-import { zod, ZodOverride } from "../../src/util/effect-zod"
+import { toJsonSchema, zod, ZodOverride, ZodPreprocess } from "../../src/util/effect-zod"
 
 function json(schema: z.ZodTypeAny) {
   const { $schema: _, ...rest } = z.toJSONSchema(schema)
@@ -750,5 +750,35 @@ describe("util.effect-zod", () => {
       expect(schema.parse({})).toEqual({})
       expect(schema.parse({ foo: "hi" })).toEqual({ foo: "hi" })
     })
+
+    test("key defaults fill in missing struct keys", () => {
+      const schema = zod(
+        Schema.Struct({
+          mode: Schema.String.pipe(Schema.withDecodingDefaultTypeKey(Effect.succeed("ctrl-x"))),
+        }),
+      )
+
+      expect(schema.parse({})).toEqual({ mode: "ctrl-x" })
+    })
+
+    test("key defaults still accept explicit values", () => {
+      const schema = zod(
+        Schema.Struct({
+          mode: Schema.String.pipe(Schema.withDecodingDefaultTypeKey(Effect.succeed("ctrl-x"))),
+        }),
+      )
+
+      expect(schema.parse({ mode: "ctrl-c" })).toEqual({ mode: "ctrl-c" })
+    })
+
+    test("JSON Schema output includes the default key for key defaults", () => {
+      const shape = toJsonSchema(
+        Schema.Struct({
+          mode: Schema.String.pipe(Schema.withDecodingDefaultTypeKey(Effect.succeed("ctrl-x"))),
+        }),
+      ) as any
+      expect(shape.properties.mode.default).toBe("ctrl-x")
+      expect(shape.required).toBeUndefined()
+    })
   })
 })

packages/sdk/js/src/v2/gen/types.gen.ts

@@ -1058,31 +1058,31 @@ export type SyncEventSessionUpdated = {
   data: {
     sessionID: string
     info: {
-      id: string | null
-      slug: string | null
-      projectID: string | null
-      workspaceID: string | null
-      directory: string | null
-      parentID: string | null
-      summary: {
+      id?: string | null
+      slug?: string | null
+      projectID?: string | null
+      workspaceID?: string | null
+      directory?: string | null
+      parentID?: string | null
+      summary?: {
         additions: number
         deletions: number
         files: number
         diffs?: Array<SnapshotFileDiff>
       } | null
       share?: {
-        url: string | null
+        url?: string | null
       }
-      title: string | null
-      version: string | null
+      title?: string | null
+      version?: string | null
       time?: {
-        created: number | null
-        updated: number | null
-        compacting: number | null
-        archived: number | null
+        created?: number | null
+        updated?: number | null
+        compacting?: number | null
+        archived?: number | null
       }
-      permission: PermissionRuleset | null
-      revert: {
+      permission?: PermissionRuleset | null
+      revert?: {
         messageID: string
         partID?: string
         snapshot?: string

packages/sdk/openapi.json

@@ -6804,7 +6804,6 @@
                   },
                   "duration": {
                     "description": "Duration in milliseconds",
-                    "default": 5000,
                     "type": "number"
                   }
                 },
@@ -7638,20 +7637,8 @@
                 "type": "string"
               },
               "event": {
-                "anyOf": [
-                  {
-                    "type": "string",
-                    "const": "add"
-                  },
-                  {
-                    "type": "string",
-                    "const": "change"
-                  },
-                  {
-                    "type": "string",
-                    "const": "unlink"
-                  }
-                ]
+                "type": "string",
+                "enum": ["add", "change", "unlink"]
               }
             },
             "required": ["file", "event"]
@@ -8507,7 +8494,6 @@
               },
               "duration": {
                 "description": "Duration in milliseconds",
-                "default": 5000,
                 "type": "number"
               }
             },
@@ -10570,8 +10556,7 @@
                           }
                         ]
                       }
-                    },
-                    "required": ["url"]
+                    }
                   },
                   "title": {
                     "anyOf": [
@@ -10636,8 +10621,7 @@
                           }
                         ]
                       }
-                    },
-                    "required": ["created", "updated", "compacting", "archived"]
+                    }
                   },
                   "permission": {
                     "anyOf": [
@@ -10676,20 +10660,7 @@
                       }
                     ]
                   }
-                },
-                "required": [
-                  "id",
-                  "slug",
-                  "projectID",
-                  "workspaceID",
-                  "directory",
-                  "parentID",
-                  "summary",
-                  "title",
-                  "version",
-                  "permission",
-                  "revert"
-                ]
+                }
               }
             },
             "required": ["sessionID", "info"]