diff --git a/packages/core/src/tool/plugin/edit.ts b/packages/core/src/tool/plugin/edit.ts
index ccab3ff8eb2..4fe50ed30ab 100644
--- a/packages/core/src/tool/plugin/edit.ts
+++ b/packages/core/src/tool/plugin/edit.ts
@@ -10,13 +10,13 @@ import type { Context as PluginContext } from "@opencode-ai/plugin/effect/plugin
 import { ToolFailure } from "@opencode-ai/ai"
 import { FileDiff } from "@opencode-ai/schema/file-diff"
 import { Bom } from "@opencode-ai/util/bom"
-import { createTwoFilesPatch, diffLines } from "diff"
 import { Effect, Schema } from "effect"
 import { FileMutation } from "../../file-mutation"
 import { Formatter } from "../../formatter"
 import { FSUtil } from "@opencode-ai/util/fs-util"
 import { LocationMutation } from "../../location-mutation"
 import { Permission } from "../../permission"
+import { fileDiff } from "./file-diff"
 
 export const name = "edit"
 
@@ -238,19 +238,3 @@ export const Plugin = {
       .pipe(Effect.orDie)
   }),
 }
-
-function fileDiff(file: string, before: string, after: string): typeof FileDiff.Info.Type {
-  const counts = diffLines(before, after).reduce(
-    (result, item) => ({
-      additions: result.additions + (item.added ? (item.count ?? 0) : 0),
-      deletions: result.deletions + (item.removed ? (item.count ?? 0) : 0),
-    }),
-    { additions: 0, deletions: 0 },
-  )
-  return {
-    file,
-    patch: createTwoFilesPatch(file, file, before, after),
-    status: "modified",
-    ...counts,
-  }
-}
diff --git a/packages/core/src/tool/plugin/file-diff.ts b/packages/core/src/tool/plugin/file-diff.ts
new file mode 100644
index 00000000000..250390c0f4a
--- /dev/null
+++ b/packages/core/src/tool/plugin/file-diff.ts
@@ -0,0 +1,23 @@
+import { FileDiff } from "@opencode-ai/schema/file-diff"
+import { createTwoFilesPatch, diffLines } from "diff"
+
+export function fileDiff(
+  file: string,
+  before: string,
+  after: string,
+  status: typeof FileDiff.Info.Type.status = "modified",
+): typeof FileDiff.Info.Type {
+  const counts = diffLines(before, after).reduce(
+    (result, item) => ({
+      additions: result.additions + (item.added ? (item.count ?? 0) : 0),
+      deletions: result.deletions + (item.removed ? (item.count ?? 0) : 0),
+    }),
+    { additions: 0, deletions: 0 },
+  )
+  return {
+    file,
+    patch: createTwoFilesPatch(file, file, before, after),
+    status,
+    ...counts,
+  }
+}
diff --git a/packages/core/src/tool/plugin/write.ts b/packages/core/src/tool/plugin/write.ts
index 0d91d6db029..332ade279e1 100644
--- a/packages/core/src/tool/plugin/write.ts
+++ b/packages/core/src/tool/plugin/write.ts
@@ -8,15 +8,14 @@ export * as WriteTool from "./write"
 
 import type { Context as PluginContext } from "@opencode-ai/plugin/effect/plugin"
 import { ToolFailure } from "@opencode-ai/ai"
-import { FileDiff } from "@opencode-ai/schema/file-diff"
 import { Effect, Schema } from "effect"
-import { createTwoFilesPatch, diffLines } from "diff"
 import { Bom } from "@opencode-ai/util/bom"
 import { FSUtil } from "@opencode-ai/util/fs-util"
 import { FileMutation } from "../../file-mutation"
 import { Formatter } from "../../formatter"
 import { LocationMutation } from "../../location-mutation"
 import { Permission } from "../../permission"
+import { fileDiff } from "./file-diff"
 
 export const name = "write"
 
@@ -83,19 +82,12 @@ export const Plugin = {
                     Effect.catchReason("PlatformError", "NotFound", () => Effect.succeed(undefined)),
                   )
                   const next = Bom.split(input.content)
-                  const counts = diffLines(current?.text ?? "", next.text).reduce(
-                    (result, item) => ({
-                      additions: result.additions + (item.added ? (item.count ?? 0) : 0),
-                      deletions: result.deletions + (item.removed ? (item.count ?? 0) : 0),
-                    }),
-                    { additions: 0, deletions: 0 },
+                  const preview = fileDiff(
+                    target.resource,
+                    current?.text ?? "",
+                    next.text,
+                    current ? "modified" : "added",
                   )
-                  const preview: typeof FileDiff.Info.Type = {
-                    file: target.resource,
-                    patch: createTwoFilesPatch(target.resource, target.resource, current?.text ?? "", next.text),
-                    status: current ? "modified" : "added",
-                    ...counts,
-                  }
                   yield* permission.assert({
                     action: "edit",
                     resources: [target.resource],