diff --git a/packages/opencode/src/bus/index.ts b/packages/opencode/src/bus/index.ts
index ae40d9cd96..464af05c72 100644
--- a/packages/opencode/src/bus/index.ts
+++ b/packages/opencode/src/bus/index.ts
@@ -166,6 +166,8 @@ export namespace Bus {
 
   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"]>) {
     return runPromise((svc) => svc.publish(def, properties))
   }
diff --git a/packages/opencode/test/bus/bus-effect.test.ts b/packages/opencode/test/bus/bus-effect.test.ts
index 6652f24b33..4c3b9d085d 100644
--- a/packages/opencode/test/bus/bus-effect.test.ts
+++ b/packages/opencode/test/bus/bus-effect.test.ts
@@ -4,8 +4,7 @@ import z from "zod"
 import { Bus } from "../../src/bus"
 import { BusEvent } from "../../src/bus/bus-event"
 import { Instance } from "../../src/project/instance"
-import { tmpdir } from "../fixture/fixture"
-import { provideInstance } from "../fixture/instance"
+import { provideInstance, tmpdir } from "../fixture/fixture"
 
 const TestEvent = {
   Ping: BusEvent.define("test.effect.ping", z.object({ value: z.number() })),
diff --git a/packages/opencode/test/file/watcher.test.ts b/packages/opencode/test/file/watcher.test.ts
index 8cbd478cba..9835757b17 100644
--- a/packages/opencode/test/file/watcher.test.ts
+++ b/packages/opencode/test/file/watcher.test.ts
@@ -2,9 +2,8 @@ import { $ } from "bun"
 import { afterEach, describe, expect, test } from "bun:test"
 import fs from "fs/promises"
 import path from "path"
-import { Deferred, Effect, Option } from "effect"
+import { ConfigProvider, Deferred, Effect, Layer, ManagedRuntime, Option } from "effect"
 import { tmpdir } from "../fixture/fixture"
-import { watcherConfigLayer, withServices } from "../fixture/instance"
 import { Bus } from "../../src/bus"
 import { FileWatcher } from "../../src/file/watcher"
 import { Instance } from "../../src/project/instance"
@@ -16,20 +15,33 @@ const describeWatcher = FileWatcher.hasNativeBinding() && !process.env.CI ? desc
 // Helpers
 // ---------------------------------------------------------------------------
 
+const watcherConfigLayer = ConfigProvider.layer(
+  ConfigProvider.fromUnknown({
+    OPENCODE_EXPERIMENTAL_FILEWATCHER: "true",
+    OPENCODE_EXPERIMENTAL_DISABLE_FILEWATCHER: "false",
+  }),
+)
+
 type WatcherEvent = { file: string; event: "add" | "change" | "unlink" }
 
 /** Run `body` with a live FileWatcher service. */
 function withWatcher<E>(directory: string, body: Effect.Effect<void, E>) {
-  return withServices(
+  return Instance.provide({
     directory,
-    FileWatcher.layer,
-    async (rt) => {
-      await rt.runPromise(FileWatcher.Service.use((s) => s.init()))
-      await Effect.runPromise(ready(directory))
-      await Effect.runPromise(body)
+    fn: async () => {
+      const layer: Layer.Layer<FileWatcher.Service, never, never> = FileWatcher.layer.pipe(
+        Layer.provide(watcherConfigLayer),
+      )
+      const rt = ManagedRuntime.make(layer)
+      try {
+        await rt.runPromise(FileWatcher.Service.use((s) => s.init()))
+        await Effect.runPromise(ready(directory))
+        await Effect.runPromise(body)
+      } finally {
+        await rt.dispose()
+      }
     },
-    { provide: [watcherConfigLayer] },
-  )
+  })
 }
 
 function listen(directory: string, check: (evt: WatcherEvent) => boolean, hit: (evt: WatcherEvent) => void) {
diff --git a/packages/opencode/test/fixture/fixture.ts b/packages/opencode/test/fixture/fixture.ts
index 0fc1576180..776c6d52f6 100644
--- a/packages/opencode/test/fixture/fixture.ts
+++ b/packages/opencode/test/fixture/fixture.ts
@@ -5,6 +5,7 @@ import path from "path"
 import { Effect, FileSystem } from "effect"
 import { ChildProcess, ChildProcessSpawner } from "effect/unstable/process"
 import type { Config } from "../../src/config/config"
+import { Instance } from "../../src/project/instance"
 
 // Strip null bytes from paths (defensive fix for CI environment issues)
 function sanitizePath(p: string): string {
@@ -81,11 +82,10 @@ export function tmpdirScoped(options?: { git?: boolean; config?: Partial<Config.
     const spawner = yield* ChildProcessSpawner.ChildProcessSpawner
     const dir = yield* fs.makeTempDirectoryScoped({ prefix: "opencode-test-" })
 
-    function git(...args: string[]) {
-      return spawner.spawn(ChildProcess.make("git", args, { cwd: dir })).pipe(
-        Effect.flatMap((handle) => handle.exitCode),
-      )
-    }
+    const git = (...args: string[]) =>
+      spawner
+        .spawn(ChildProcess.make("git", args, { cwd: dir }))
+        .pipe(Effect.flatMap((handle) => handle.exitCode))
 
     if (options?.git) {
       yield* git("init")
@@ -105,3 +105,22 @@ export function tmpdirScoped(options?: { git?: boolean; config?: Partial<Config.
     return dir
   })
 }
+
+export const provideInstance =
+  (directory: string) =>
+  <A, E, R>(self: Effect.Effect<A, E, R>): Effect.Effect<A, E, R> =>
+    Effect.withFiber((fiber) =>
+      Effect.promise<A>(async () =>
+        Instance.provide({
+          directory,
+          fn: () => Effect.runPromiseWith(fiber.services as any)(self),
+        }),
+      ),
+    )
+
+export function tmpdirInstanceScoped(options?: { git?: boolean; config?: Partial<Config.Info> }) {
+  return Effect.map(tmpdirScoped(options), (path) => ({
+    path,
+    provide: provideInstance(path),
+  }))
+}
diff --git a/packages/opencode/test/fixture/instance.ts b/packages/opencode/test/fixture/instance.ts
index ebe1a3ef12..6f30846a43 100644
--- a/packages/opencode/test/fixture/instance.ts
+++ b/packages/opencode/test/fixture/instance.ts
@@ -43,12 +43,12 @@ export function withServices<S>(
 
 export const provideInstance =
   (directory: string) =>
-  <A, E, R>(self: Effect.Effect<A, E, R>): Effect.Effect<A, E, R> =>
-    Effect.withFiber((fiber) =>
+  <A, E = never, R = never>(self: Effect.Effect<A, E, R>): Effect.Effect<A, E, R> =>
+    Effect.services<A, E, R>((fiber) =>
       Effect.promise<A>(async () =>
         Instance.provide({
           directory,
-          fn: () => Effect.runPromiseWith(fiber.services as any)(self),
+          fn: () => Effect.runPromiseWith(fiber.services)(self),
         }),
       ),
     )
diff --git a/packages/opencode/test/format/format.test.ts b/packages/opencode/test/format/format.test.ts
index 06e3ef9b35..d081090d6c 100644
--- a/packages/opencode/test/format/format.test.ts
+++ b/packages/opencode/test/format/format.test.ts
@@ -1,13 +1,28 @@
-import { Effect } from "effect"
+import { Effect, Layer, ManagedRuntime } from "effect"
 import { afterEach, describe, expect, test } from "bun:test"
 import { tmpdir } from "../fixture/fixture"
-import { withServices } from "../fixture/instance"
-import { Bus } from "../../src/bus"
-import { File } from "../../src/file"
 import { Format } from "../../src/format"
 import * as Formatter from "../../src/format/formatter"
 import { Instance } from "../../src/project/instance"
 
+function withRuntime<S, E>(
+  directory: string,
+  layer: Layer.Layer<S, E, never>,
+  body: (rt: ManagedRuntime.ManagedRuntime<S, E>) => Promise<void>,
+) {
+  return Instance.provide({
+    directory,
+    fn: async () => {
+      const rt = ManagedRuntime.make(layer)
+      try {
+        await body(rt)
+      } finally {
+        await rt.dispose()
+      }
+    },
+  })
+}
+
 describe("Format", () => {
   afterEach(async () => {
     await Instance.disposeAll()
@@ -16,7 +31,7 @@ describe("Format", () => {
   test("status() returns built-in formatters when no config overrides", async () => {
     await using tmp = await tmpdir()
 
-    await withServices(tmp.path, Format.layer, async (rt) => {
+    await withRuntime(tmp.path, Format.layer, async (rt) => {
       const statuses = await rt.runPromise(Format.Service.use((s) => s.status()))
       expect(Array.isArray(statuses)).toBe(true)
       expect(statuses.length).toBeGreaterThan(0)
@@ -38,7 +53,7 @@ describe("Format", () => {
       config: { formatter: false },
     })
 
-    await withServices(tmp.path, Format.layer, async (rt) => {
+    await withRuntime(tmp.path, Format.layer, async (rt) => {
       const statuses = await rt.runPromise(Format.Service.use((s) => s.status()))
       expect(statuses).toEqual([])
     })
@@ -53,7 +68,7 @@ describe("Format", () => {
       },
     })
 
-    await withServices(tmp.path, Format.layer, async (rt) => {
+    await withRuntime(tmp.path, Format.layer, async (rt) => {
       const statuses = await rt.runPromise(Format.Service.use((s) => s.status()))
       const gofmt = statuses.find((s) => s.name === "gofmt")
       expect(gofmt).toBeUndefined()
@@ -63,7 +78,7 @@ describe("Format", () => {
   test("service initializes without error", async () => {
     await using tmp = await tmpdir()
 
-    await withServices(tmp.path, Format.layer, async (rt) => {
+    await withRuntime(tmp.path, Format.layer, async (rt) => {
       await rt.runPromise(Format.Service.use(() => Effect.void))
     })
   })
@@ -127,7 +142,7 @@ describe("Format", () => {
     }
 
     try {
-      await withServices(tmp.path, Format.layer, async (rt) => {
+      await withRuntime(tmp.path, Format.layer, async (rt) => {
         await rt.runPromise(Format.Service.use((s) => s.init()))
         await rt.runPromise(Format.Service.use((s) => s.file(file)))
       })
@@ -162,7 +177,7 @@ describe("Format", () => {
     const file = `${tmp.path}/test.seq`
     await Bun.write(file, "x")
 
-    await withServices(tmp.path, Format.layer, async (rt) => {
+    await withRuntime(tmp.path, Format.layer, async (rt) => {
       await rt.runPromise(Format.Service.use((s) => s.init()))
       await rt.runPromise(Format.Service.use((s) => s.file(file)))
     })