diff --git a/packages/opencode/src/tool/write.ts b/packages/opencode/src/tool/write.ts
index 6b134e5253de..c28e33667961 100644
--- a/packages/opencode/src/tool/write.ts
+++ b/packages/opencode/src/tool/write.ts
@@ -7,7 +7,6 @@ import DESCRIPTION from "./write.txt"
 import { Bus } from "../bus"
 import { File } from "../file"
 import { FileWatcher } from "../file/watcher"
-import { Format } from "../format"
 import { FileTime } from "../file/time"
 import { Filesystem } from "../util/filesystem"
 import { Instance } from "../project/instance"
@@ -42,9 +41,10 @@ export const WriteTool = Tool.define("write", {
       },
     })
 
-    await Filesystem.write(filepath, params.content)
-    await Format.file(filepath)
-    Bus.publish(File.Event.Edited, { file: filepath })
+    await Filesystem.write(filepath, params.content, 0o644)
+    await Bus.publish(File.Event.Edited, {
+      file: filepath,
+    })
     await Bus.publish(FileWatcher.Event.Updated, {
       file: filepath,
       event: exists ? "change" : "add",
diff --git a/packages/opencode/src/util/filesystem.ts b/packages/opencode/src/util/filesystem.ts
index 29f79e9587ae..465059278070 100644
--- a/packages/opencode/src/util/filesystem.ts
+++ b/packages/opencode/src/util/filesystem.ts
@@ -62,6 +62,9 @@ export namespace Filesystem {
     try {
       if (mode) {
         await writeFile(p, content, { mode })
+        // writeFile mode is still filtered by process umask for newly created files,
+        // and won't update mode for existing files. Force the requested mode explicitly.
+        await chmod(p, mode)
       } else {
         await writeFile(p, content)
       }
@@ -70,6 +73,7 @@ export namespace Filesystem {
         await mkdir(dirname(p), { recursive: true })
         if (mode) {
           await writeFile(p, content, { mode })
+          await chmod(p, mode)
         } else {
           await writeFile(p, content)
         }