From ceb5f3554edbfb31b11dec9b96995dc7bfb2758d Mon Sep 17 00:00:00 2001
From: Shoubhit Dash <shoubhit2005@gmail.com>
Date: Mon, 6 Jul 2026 18:21:43 +0530
Subject: [PATCH] feat(plugin): bound vcs adapter diffs

---
 packages/core/src/vcs.ts                |  6 +++++-
 packages/core/src/vcs/backends.ts       | 12 ++++++++++++
 packages/core/test/vcs-backends.test.ts | 17 +++++++++++++++++
 packages/plugin/src/v2/effect/vcs.ts    | 10 ++++++----
 4 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/packages/core/src/vcs.ts b/packages/core/src/vcs.ts
index 4b30ea285e..f0e519ba47 100644
--- a/packages/core/src/vcs.ts
+++ b/packages/core/src/vcs.ts
@@ -10,6 +10,7 @@ import { AppProcess } from "./process"
 import { VcsBackends } from "./vcs/backends"
 import { VcsGit } from "./vcs/git"
 import { VcsHg } from "./vcs/hg"
+import { MAX_TOTAL_PATCH_BYTES, PATCH_CONTEXT_LINES } from "./vcs/patch"
 
 export { FileStatus, Mode }
 
@@ -60,7 +61,10 @@ const layer = Layer.effect(
       diff: Effect.fn("Vcs.diff")(function* (mode: Mode, options?: DiffOptions) {
         const impl = yield* adapter()
         if (!impl) return []
-        return yield* impl.diff(mode, options)
+        return yield* impl.diff(mode, {
+          context: options?.context ?? PATCH_CONTEXT_LINES,
+          maxOutputBytes: MAX_TOTAL_PATCH_BYTES,
+        })
       }),
     })
   }),
diff --git a/packages/core/src/vcs/backends.ts b/packages/core/src/vcs/backends.ts
index dde3585ff7..ececbc37fd 100644
--- a/packages/core/src/vcs/backends.ts
+++ b/packages/core/src/vcs/backends.ts
@@ -81,10 +81,22 @@ function guard(type: string, make: () => Vcs.Adapter): Vcs.Adapter {
       adapter.pipe(
         Effect.flatMap((impl) => impl.diff(mode, options)),
         sanitize(type, "diff", decodeDiff),
+        Effect.map((rows) => boundDiff(rows, options.maxOutputBytes)),
       ),
   }
 }
 
+function boundDiff(rows: readonly FileDiff.Info[], maxOutputBytes: number) {
+  let total = 0
+  return rows.map((row) => {
+    if (row.patch === undefined) return row
+    const bytes = Buffer.byteLength(row.patch)
+    if (total + bytes > maxOutputBytes) return { ...row, patch: undefined }
+    total += bytes
+    return row
+  })
+}
+
 function sanitize<A>(type: string, operation: string, decode: (input: unknown) => Option.Option<readonly A[]>) {
   return <E, R>(effect: Effect.Effect<readonly A[], E, R>) =>
     effect.pipe(
diff --git a/packages/core/test/vcs-backends.test.ts b/packages/core/test/vcs-backends.test.ts
index a0210ed307..7d56a85503 100644
--- a/packages/core/test/vcs-backends.test.ts
+++ b/packages/core/test/vcs-backends.test.ts
@@ -53,6 +53,23 @@ describe("VcsBackends", () => {
     }).pipe(Effect.scoped, provide),
   )
 
+  it.live("passes normalized options and bounds plugin diffs", () =>
+    Effect.gen(function* () {
+      let received: Parameters<PluginVcs.Adapter["diff"]>[1] | undefined
+      yield* register(
+        backend({
+          diff: (_mode, options) => {
+            received = options
+            return Effect.succeed([{ ...diff[0], patch: "x".repeat(options.maxOutputBytes + 1) }])
+          },
+        }),
+      )
+      const vcs = yield* Vcs.Service
+      expect(yield* vcs.diff("working", { context: 3 })).toEqual([{ ...diff[0], patch: undefined }])
+      expect(received).toEqual({ context: 3, maxOutputBytes: 10_000_000 })
+    }).pipe(Effect.scoped, provide),
+  )
+
   it.live("passes the location scope to the adapter factory", () =>
     Effect.gen(function* () {
       let scope: PluginVcs.AdapterScope | undefined
diff --git a/packages/plugin/src/v2/effect/vcs.ts b/packages/plugin/src/v2/effect/vcs.ts
index 0012575cd8..6476e36b50 100644
--- a/packages/plugin/src/v2/effect/vcs.ts
+++ b/packages/plugin/src/v2/effect/vcs.ts
@@ -15,12 +15,14 @@ export interface AdapterScope {
   readonly store: string
 }
 
+export interface DiffOptions {
+  readonly context: number
+  readonly maxOutputBytes: number
+}
+
 export interface Adapter {
   readonly status: () => Effect.Effect<readonly FileStatus[]>
-  readonly diff: (
-    mode: Mode,
-    options?: { readonly context?: number },
-  ) => Effect.Effect<readonly FileDiff.Info[]>
+  readonly diff: (mode: Mode, options: DiffOptions) => Effect.Effect<readonly FileDiff.Info[]>
 }
 
 export interface Backend {