diff --git a/packages/kilo-sandbox/src/mutation-worker.ts b/packages/kilo-sandbox/src/mutation-worker.ts
index 965cabf109c..f29909b893e 100644
--- a/packages/kilo-sandbox/src/mutation-worker.ts
+++ b/packages/kilo-sandbox/src/mutation-worker.ts
@@ -120,4 +120,6 @@ const response: Response = await read()
     (value) => ({ ok: true, value }),
     (cause) => ({ ok: false, error: failure(cause) }),
   )
-process.stdout.write(JSON.stringify(response))
+await new Promise<void>((resolve, reject) => {
+  process.stdout.write(JSON.stringify(response), (error) => (error ? reject(error) : resolve()))
+})
diff --git a/packages/kilo-sandbox/test/filesystem.test.ts b/packages/kilo-sandbox/test/filesystem.test.ts
index e0281dee6e6..6eb9bba3ba5 100644
--- a/packages/kilo-sandbox/test/filesystem.test.ts
+++ b/packages/kilo-sandbox/test/filesystem.test.ts
@@ -125,6 +125,7 @@ describe("sandbox FileSystem", () => {
       const symbolic = path.join(base, "symbolic.bin")
       const streamed = path.join(base, "streamed.bin")
       const time = new Date("2024-01-02T03:04:05.000Z")
+      const copiedTime = new Date("2023-02-03T04:05:06.000Z")
       await execute(
         run(
           makeProfile(allowed),
@@ -137,7 +138,9 @@ describe("sandbox FileSystem", () => {
             yield* fs.truncate(source, 3)
             yield* fs.utimes(source, time, time)
             yield* fs.copyFile(source, copy)
-            yield* fs.writeFileString(path.join(tree, "value.txt"), "tree")
+            const value = path.join(tree, "value.txt")
+            yield* fs.writeFileString(value, "tree")
+            yield* fs.utimes(value, copiedTime, copiedTime)
             yield* fs.copy(tree, copied, { overwrite: true, preserveTimestamps: true })
             yield* fs.link(source, hard)
             yield* fs.symlink("source.bin", symbolic)
@@ -155,8 +158,10 @@ describe("sandbox FileSystem", () => {
       expect([...(await readFile(streamed))]).toEqual([1, 2, 3, 4])
       expect(await readFile(path.join(copied, "value.txt"), "utf8")).toBe("tree")
       const info = await stat(source)
+      const copiedInfo = await stat(path.join(copied, "value.txt"))
       expect(info.mode & 0o777).toBe(0o640)
       expect(info.mtime.getTime()).toBe(time.getTime())
+      expect(copiedInfo.mtime.getTime()).toBe(copiedTime.getTime())
     },
   )
 
diff --git a/packages/opencode/test/kilocode/sandbox/session-tools.test.ts b/packages/opencode/test/kilocode/sandbox/session-tools.test.ts
index 88b1dfa3c90..4740bba61c3 100644
--- a/packages/opencode/test/kilocode/sandbox/session-tools.test.ts
+++ b/packages/opencode/test/kilocode/sandbox/session-tools.test.ts
@@ -149,6 +149,7 @@ const registry = Layer.effect(
   }),
 ).pipe(Layer.provideMerge(base))
 const it = testEffect(registry)
+const mac = process.platform === "darwin" && existsSync("/usr/bin/sandbox-exec") ? it.live : it.live.skip
 
 function resolve(ctx: InstanceContext) {
   return SessionTools.resolve({
@@ -220,7 +221,7 @@ function fixture() {
   })
 }
 
-it.live("confines model-originated file mutations to the active worktree", () =>
+mac("confines model-originated file mutations to the active worktree", () =>
   Effect.gen(function* () {
     const dirs = yield* fixture()
     const tools = yield* resolve(dirs.ctx)
@@ -279,7 +280,7 @@ it.live("confines model-originated file mutations to the active worktree", () =>
   }),
 )
 
-it.live("keeps model-originated file mutations writable in a local checkout", () =>
+mac("keeps model-originated file mutations writable in a local checkout", () =>
   Effect.gen(function* () {
     const dirs = yield* fixture()
     const ctx = context(dirs.local, dirs.main, [dirs.a, dirs.b])
@@ -295,7 +296,7 @@ it.live("keeps model-originated file mutations writable in a local checkout", ()
   }),
 )
 
-it.live("keeps concurrent session profiles call-local", () =>
+mac("keeps concurrent session profiles call-local", () =>
   Effect.gen(function* () {
     const dirs = yield* fixture()
     const left = yield* resolve(context(dirs.a, dirs.main, [dirs.a, dirs.b]))
@@ -327,8 +328,6 @@ it.live("keeps concurrent session profiles call-local", () =>
   }),
 )
 
-const mac = process.platform === "darwin" && existsSync("/usr/bin/sandbox-exec") ? it.live : it.live.skip
-
 mac("confines a model-originated sandboxed process to the active worktree", () =>
   Effect.gen(function* () {
     const dirs = yield* fixture()