diff --git a/packages/opencode/test/bus/bus-effect.test.ts b/packages/opencode/test/bus/bus-effect.test.ts
index 4c3b9d085d..cc44f9ef78 100644
--- a/packages/opencode/test/bus/bus-effect.test.ts
+++ b/packages/opencode/test/bus/bus-effect.test.ts
@@ -1,156 +1,130 @@
-import { afterEach, describe, expect, test } from "bun:test"
-import { Deferred, Effect, ManagedRuntime, Stream } from "effect"
+import { NodeChildProcessSpawner, NodeFileSystem, NodePath } from "@effect/platform-node"
+import { describe, expect } from "bun:test"
+import { Deferred, Effect, Layer, Stream } from "effect"
 import z from "zod"
 import { Bus } from "../../src/bus"
 import { BusEvent } from "../../src/bus/bus-event"
-import { Instance } from "../../src/project/instance"
-import { provideInstance, tmpdir } from "../fixture/fixture"
+import { provideTmpdirInstance } from "../fixture/fixture"
+import { testEffect } from "../lib/effect"
 
 const TestEvent = {
   Ping: BusEvent.define("test.effect.ping", z.object({ value: z.number() })),
   Pong: BusEvent.define("test.effect.pong", z.object({ message: z.string() })),
 }
 
-async function runBus<A>(directory: string, self: Effect.Effect<A, never, Bus.Service>) {
-  const rt = ManagedRuntime.make(Bus.layer)
-  try {
-    return await rt.runPromise(self.pipe(provideInstance(directory)))
-  } finally {
-    await rt.dispose()
-  }
-}
+const node = NodeChildProcessSpawner.layer.pipe(
+  Layer.provideMerge(Layer.mergeAll(NodeFileSystem.layer, NodePath.layer)),
+)
+
+const live = Layer.mergeAll(Bus.layer, node)
+
+const it = testEffect(live)
 
 describe("Bus (Effect-native)", () => {
-  afterEach(() => Instance.disposeAll())
+  it.effect("publish + subscribe stream delivers events", () =>
+    provideTmpdirInstance(() =>
+      Effect.gen(function* () {
+        const bus = yield* Bus.Service
+        const received: number[] = []
+        const done = yield* Deferred.make<void>()
 
-  test("publish + subscribe stream delivers events", async () => {
-    await using tmp = await tmpdir()
-
-    await runBus(
-      tmp.path,
-      Effect.scoped(
-        Bus.Service.use((bus) =>
-          Effect.gen(function* () {
-            const received: number[] = []
-            const done = yield* Deferred.make<void>()
-
-            yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
-              Effect.sync(() => {
-                received.push(evt.properties.value)
-                if (received.length === 2) Deferred.doneUnsafe(done, Effect.void)
-              }),
-            ).pipe(Effect.forkScoped)
-
-            yield* Effect.sleep("10 millis")
-            yield* bus.publish(TestEvent.Ping, { value: 1 })
-            yield* bus.publish(TestEvent.Ping, { value: 2 })
-            yield* Deferred.await(done)
-
-            expect(received).toEqual([1, 2])
+        yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
+          Effect.sync(() => {
+            received.push(evt.properties.value)
+            if (received.length === 2) Deferred.doneUnsafe(done, Effect.void)
           }),
-        ),
-      ),
-    )
-  })
+        ).pipe(Effect.forkScoped)
 
-  test("subscribe filters by event type", async () => {
-    await using tmp = await tmpdir()
+        yield* Effect.sleep("10 millis")
+        yield* bus.publish(TestEvent.Ping, { value: 1 })
+        yield* bus.publish(TestEvent.Ping, { value: 2 })
+        yield* Deferred.await(done)
 
-    await runBus(
-      tmp.path,
-      Effect.scoped(
-        Bus.Service.use((bus) =>
-          Effect.gen(function* () {
-            const pings: number[] = []
-            const done = yield* Deferred.make<void>()
+        expect(received).toEqual([1, 2])
+      }),
+    ),
+  )
 
-            yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
-              Effect.sync(() => {
-                pings.push(evt.properties.value)
-                Deferred.doneUnsafe(done, Effect.void)
-              }),
-            ).pipe(Effect.forkScoped)
+  it.effect("subscribe filters by event type", () =>
+    provideTmpdirInstance(() =>
+      Effect.gen(function* () {
+        const bus = yield* Bus.Service
+        const pings: number[] = []
+        const done = yield* Deferred.make<void>()
 
-            yield* Effect.sleep("10 millis")
-            yield* bus.publish(TestEvent.Pong, { message: "ignored" })
-            yield* bus.publish(TestEvent.Ping, { value: 42 })
-            yield* Deferred.await(done)
-
-            expect(pings).toEqual([42])
+        yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
+          Effect.sync(() => {
+            pings.push(evt.properties.value)
+            Deferred.doneUnsafe(done, Effect.void)
           }),
-        ),
-      ),
-    )
-  })
+        ).pipe(Effect.forkScoped)
 
-  test("subscribeAll receives all types", async () => {
-    await using tmp = await tmpdir()
+        yield* Effect.sleep("10 millis")
+        yield* bus.publish(TestEvent.Pong, { message: "ignored" })
+        yield* bus.publish(TestEvent.Ping, { value: 42 })
+        yield* Deferred.await(done)
 
-    await runBus(
-      tmp.path,
-      Effect.scoped(
-        Bus.Service.use((bus) =>
-          Effect.gen(function* () {
-            const types: string[] = []
-            const done = yield* Deferred.make<void>()
+        expect(pings).toEqual([42])
+      }),
+    ),
+  )
 
-            yield* Stream.runForEach(bus.subscribeAll(), (evt) =>
-              Effect.sync(() => {
-                types.push(evt.type)
-                if (types.length === 2) Deferred.doneUnsafe(done, Effect.void)
-              }),
-            ).pipe(Effect.forkScoped)
+  it.effect("subscribeAll receives all types", () =>
+    provideTmpdirInstance(() =>
+      Effect.gen(function* () {
+        const bus = yield* Bus.Service
+        const types: string[] = []
+        const done = yield* Deferred.make<void>()
 
-            yield* Effect.sleep("10 millis")
-            yield* bus.publish(TestEvent.Ping, { value: 1 })
-            yield* bus.publish(TestEvent.Pong, { message: "hi" })
-            yield* Deferred.await(done)
-
-            expect(types).toContain("test.effect.ping")
-            expect(types).toContain("test.effect.pong")
+        yield* Stream.runForEach(bus.subscribeAll(), (evt) =>
+          Effect.sync(() => {
+            types.push(evt.type)
+            if (types.length === 2) Deferred.doneUnsafe(done, Effect.void)
           }),
-        ),
-      ),
-    )
-  })
+        ).pipe(Effect.forkScoped)
 
-  test("multiple subscribers each receive the event", async () => {
-    await using tmp = await tmpdir()
+        yield* Effect.sleep("10 millis")
+        yield* bus.publish(TestEvent.Ping, { value: 1 })
+        yield* bus.publish(TestEvent.Pong, { message: "hi" })
+        yield* Deferred.await(done)
 
-    await runBus(
-      tmp.path,
-      Effect.scoped(
-        Bus.Service.use((bus) =>
-          Effect.gen(function* () {
-            const a: number[] = []
-            const b: number[] = []
-            const doneA = yield* Deferred.make<void>()
-            const doneB = yield* Deferred.make<void>()
+        expect(types).toContain("test.effect.ping")
+        expect(types).toContain("test.effect.pong")
+      }),
+    ),
+  )
 
-            yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
-              Effect.sync(() => {
-                a.push(evt.properties.value)
-                Deferred.doneUnsafe(doneA, Effect.void)
-              }),
-            ).pipe(Effect.forkScoped)
+  it.effect("multiple subscribers each receive the event", () =>
+    provideTmpdirInstance(() =>
+      Effect.gen(function* () {
+        const bus = yield* Bus.Service
+        const a: number[] = []
+        const b: number[] = []
+        const doneA = yield* Deferred.make<void>()
+        const doneB = yield* Deferred.make<void>()
 
-            yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
-              Effect.sync(() => {
-                b.push(evt.properties.value)
-                Deferred.doneUnsafe(doneB, Effect.void)
-              }),
-            ).pipe(Effect.forkScoped)
-
-            yield* Effect.sleep("10 millis")
-            yield* bus.publish(TestEvent.Ping, { value: 99 })
-            yield* Deferred.await(doneA)
-            yield* Deferred.await(doneB)
-
-            expect(a).toEqual([99])
-            expect(b).toEqual([99])
+        yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
+          Effect.sync(() => {
+            a.push(evt.properties.value)
+            Deferred.doneUnsafe(doneA, Effect.void)
           }),
-        ),
-      ),
-    )
-  })
+        ).pipe(Effect.forkScoped)
+
+        yield* Stream.runForEach(bus.subscribe(TestEvent.Ping), (evt) =>
+          Effect.sync(() => {
+            b.push(evt.properties.value)
+            Deferred.doneUnsafe(doneB, Effect.void)
+          }),
+        ).pipe(Effect.forkScoped)
+
+        yield* Effect.sleep("10 millis")
+        yield* bus.publish(TestEvent.Ping, { value: 99 })
+        yield* Deferred.await(doneA)
+        yield* Deferred.await(doneB)
+
+        expect(a).toEqual([99])
+        expect(b).toEqual([99])
+      }),
+    ),
+  )
 })
diff --git a/packages/opencode/test/fixture/fixture.ts b/packages/opencode/test/fixture/fixture.ts
index 776c6d52f6..a36a3f9d84 100644
--- a/packages/opencode/test/fixture/fixture.ts
+++ b/packages/opencode/test/fixture/fixture.ts
@@ -2,7 +2,7 @@ import { $ } from "bun"
 import * as fs from "fs/promises"
 import os from "os"
 import path from "path"
-import { Effect, FileSystem } from "effect"
+import { Effect, FileSystem, ServiceMap } from "effect"
 import { ChildProcess, ChildProcessSpawner } from "effect/unstable/process"
 import type { Config } from "../../src/config/config"
 import { Instance } from "../../src/project/instance"
@@ -75,7 +75,7 @@ export async function tmpdir<T>(options?: TmpDirOptions<T>) {
   return result
 }
 
-/** Effectful scoped tmpdir — cleaned up when the scope closes */
+/** Effectful scoped tmpdir. Cleaned up when the scope closes. Make sure these stay in sync */
 export function tmpdirScoped(options?: { git?: boolean; config?: Partial<Config.Info> }) {
   return Effect.gen(function* () {
     const fs = yield* FileSystem.FileSystem
@@ -83,9 +83,7 @@ export function tmpdirScoped(options?: { git?: boolean; config?: Partial<Config.
     const dir = yield* fs.makeTempDirectoryScoped({ prefix: "opencode-test-" })
 
     const git = (...args: string[]) =>
-      spawner
-        .spawn(ChildProcess.make("git", args, { cwd: dir }))
-        .pipe(Effect.flatMap((handle) => handle.exitCode))
+      spawner.spawn(ChildProcess.make("git", args, { cwd: dir })).pipe(Effect.flatMap((handle) => handle.exitCode))
 
     if (options?.git) {
       yield* git("init")
@@ -109,18 +107,35 @@ export function tmpdirScoped(options?: { git?: boolean; config?: Partial<Config.
 export const provideInstance =
   (directory: string) =>
   <A, E, R>(self: Effect.Effect<A, E, R>): Effect.Effect<A, E, R> =>
-    Effect.withFiber((fiber) =>
+    Effect.servicesWith((services: ServiceMap.ServiceMap<R>) =>
       Effect.promise<A>(async () =>
         Instance.provide({
           directory,
-          fn: () => Effect.runPromiseWith(fiber.services as any)(self),
+          fn: () => Effect.runPromiseWith(services)(self),
         }),
       ),
     )
 
-export function tmpdirInstanceScoped(options?: { git?: boolean; config?: Partial<Config.Info> }) {
-  return Effect.map(tmpdirScoped(options), (path) => ({
-    path,
-    provide: provideInstance(path),
-  }))
+export function provideTmpdirInstance<A, E, R>(
+  self: (path: string) => Effect.Effect<A, E, R>,
+  options?: { git?: boolean; config?: Partial<Config.Info> },
+) {
+  return Effect.gen(function* () {
+    const path = yield* tmpdirScoped(options)
+    let provided = false
+
+    yield* Effect.addFinalizer(() =>
+      provided
+        ? Effect.promise(() =>
+            Instance.provide({
+              directory: path,
+              fn: () => Instance.dispose(),
+            }),
+          ).pipe(Effect.ignore)
+        : Effect.void,
+    )
+
+    provided = true
+    return yield* self(path).pipe(provideInstance(path))
+  })
 }
diff --git a/packages/opencode/test/fixture/instance.ts b/packages/opencode/test/fixture/instance.ts
deleted file mode 100644
index 6f30846a43..0000000000
--- a/packages/opencode/test/fixture/instance.ts
+++ /dev/null
@@ -1,54 +0,0 @@
-import { ConfigProvider, Effect, Layer, ManagedRuntime } from "effect"
-import { Instance } from "../../src/project/instance"
-
-/** ConfigProvider that enables the experimental file watcher. */
-export const watcherConfigLayer = ConfigProvider.layer(
-  ConfigProvider.fromUnknown({
-    OPENCODE_EXPERIMENTAL_FILEWATCHER: "true",
-    OPENCODE_EXPERIMENTAL_DISABLE_FILEWATCHER: "false",
-  }),
-)
-
-/**
- * Boot an Instance with the given service layers and run `body` with
- * the ManagedRuntime. Cleanup is automatic — the runtime is disposed
- * when `body` completes.
- *
- * Pass extra layers via `options.provide` (e.g. ConfigProvider.layer).
- */
-export function withServices<S>(
-  directory: string,
-  layer: Layer.Layer<S, any>,
-  body: (rt: ManagedRuntime.ManagedRuntime<S, never>) => Promise<void>,
-  options?: { provide?: Layer.Layer<never>[] },
-) {
-  return Instance.provide({
-    directory,
-    fn: async () => {
-      let resolved: Layer.Layer<S> = layer as any
-      if (options?.provide) {
-        for (const l of options.provide) {
-          resolved = resolved.pipe(Layer.provide(l)) as any
-        }
-      }
-      const rt = ManagedRuntime.make(resolved)
-      try {
-        await body(rt)
-      } finally {
-        await rt.dispose()
-      }
-    },
-  })
-}
-
-export const provideInstance =
-  (directory: string) =>
-  <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)(self),
-        }),
-      ),
-    )
diff --git a/packages/opencode/test/format/format.test.ts b/packages/opencode/test/format/format.test.ts
index d081090d6c..c718c13e8b 100644
--- a/packages/opencode/test/format/format.test.ts
+++ b/packages/opencode/test/format/format.test.ts
@@ -1,187 +1,182 @@
-import { Effect, Layer, ManagedRuntime } from "effect"
-import { afterEach, describe, expect, test } from "bun:test"
-import { tmpdir } from "../fixture/fixture"
+import { NodeChildProcessSpawner, NodeFileSystem, NodePath } from "@effect/platform-node"
+import { describe, expect } from "bun:test"
+import { Effect, Layer } from "effect"
+import { provideTmpdirInstance } from "../fixture/fixture"
+import { testEffect } from "../lib/effect"
 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()
-      }
-    },
-  })
-}
+const node = NodeChildProcessSpawner.layer.pipe(
+  Layer.provideMerge(Layer.mergeAll(NodeFileSystem.layer, NodePath.layer)),
+)
+
+const it = testEffect(Layer.mergeAll(Format.layer, node))
 
 describe("Format", () => {
-  afterEach(async () => {
-    await Instance.disposeAll()
-  })
+  it.effect("status() returns built-in formatters when no config overrides", () =>
+    provideTmpdirInstance(() =>
+      Format.Service.use((fmt) =>
+        Effect.gen(function* () {
+          const statuses = yield* fmt.status()
+          expect(Array.isArray(statuses)).toBe(true)
+          expect(statuses.length).toBeGreaterThan(0)
 
-  test("status() returns built-in formatters when no config overrides", async () => {
-    await using tmp = await tmpdir()
+          for (const item of statuses) {
+            expect(typeof item.name).toBe("string")
+            expect(Array.isArray(item.extensions)).toBe(true)
+            expect(typeof item.enabled).toBe("boolean")
+          }
 
-    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)
+          const gofmt = statuses.find((item) => item.name === "gofmt")
+          expect(gofmt).toBeDefined()
+          expect(gofmt!.extensions).toContain(".go")
+        }),
+      ),
+    ),
+  )
 
-      for (const s of statuses) {
-        expect(typeof s.name).toBe("string")
-        expect(Array.isArray(s.extensions)).toBe(true)
-        expect(typeof s.enabled).toBe("boolean")
-      }
+  it.effect("status() returns empty list when formatter is disabled", () =>
+    provideTmpdirInstance(
+      () =>
+        Format.Service.use((fmt) =>
+          Effect.gen(function* () {
+            expect(yield* fmt.status()).toEqual([])
+          }),
+        ),
+      { config: { formatter: false } },
+    ),
+  )
 
-      const gofmt = statuses.find((s) => s.name === "gofmt")
-      expect(gofmt).toBeDefined()
-      expect(gofmt!.extensions).toContain(".go")
-    })
-  })
-
-  test("status() returns empty list when formatter is disabled", async () => {
-    await using tmp = await tmpdir({
-      config: { formatter: false },
-    })
-
-    await withRuntime(tmp.path, Format.layer, async (rt) => {
-      const statuses = await rt.runPromise(Format.Service.use((s) => s.status()))
-      expect(statuses).toEqual([])
-    })
-  })
-
-  test("status() excludes formatters marked as disabled in config", async () => {
-    await using tmp = await tmpdir({
-      config: {
-        formatter: {
-          gofmt: { disabled: true },
+  it.effect("status() excludes formatters marked as disabled in config", () =>
+    provideTmpdirInstance(
+      () =>
+        Format.Service.use((fmt) =>
+          Effect.gen(function* () {
+            const statuses = yield* fmt.status()
+            const gofmt = statuses.find((item) => item.name === "gofmt")
+            expect(gofmt).toBeUndefined()
+          }),
+        ),
+      {
+        config: {
+          formatter: {
+            gofmt: { disabled: true },
+          },
         },
       },
-    })
+    ),
+  )
 
-    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()
-    })
-  })
+  it.effect("service initializes without error", () =>
+    provideTmpdirInstance(() => Format.Service.use(() => Effect.void)),
+  )
 
-  test("service initializes without error", async () => {
-    await using tmp = await tmpdir()
-
-    await withRuntime(tmp.path, Format.layer, async (rt) => {
-      await rt.runPromise(Format.Service.use(() => Effect.void))
-    })
-  })
-
-  test("status() initializes formatter state per directory", async () => {
-    await using off = await tmpdir({
-      config: { formatter: false },
-    })
-    await using on = await tmpdir()
-
-    const a = await Instance.provide({
-      directory: off.path,
-      fn: () => Format.status(),
-    })
-    const b = await Instance.provide({
-      directory: on.path,
-      fn: () => Format.status(),
-    })
-
-    expect(a).toEqual([])
-    expect(b.length).toBeGreaterThan(0)
-  })
-
-  test("runs enabled checks for matching formatters in parallel", async () => {
-    await using tmp = await tmpdir()
-
-    const file = `${tmp.path}/test.parallel`
-    await Bun.write(file, "x")
-
-    const one = {
-      extensions: Formatter.gofmt.extensions,
-      enabled: Formatter.gofmt.enabled,
-      command: Formatter.gofmt.command,
-    }
-    const two = {
-      extensions: Formatter.mix.extensions,
-      enabled: Formatter.mix.enabled,
-      command: Formatter.mix.command,
-    }
-
-    let active = 0
-    let max = 0
-
-    Formatter.gofmt.extensions = [".parallel"]
-    Formatter.mix.extensions = [".parallel"]
-    Formatter.gofmt.command = ["sh", "-c", "true"]
-    Formatter.mix.command = ["sh", "-c", "true"]
-    Formatter.gofmt.enabled = async () => {
-      active++
-      max = Math.max(max, active)
-      await Bun.sleep(20)
-      active--
-      return true
-    }
-    Formatter.mix.enabled = async () => {
-      active++
-      max = Math.max(max, active)
-      await Bun.sleep(20)
-      active--
-      return true
-    }
-
-    try {
-      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)))
+  it.effect("status() initializes formatter state per directory", () =>
+    Effect.gen(function* () {
+      const a = yield* provideTmpdirInstance(() => Format.Service.use((fmt) => fmt.status()), {
+        config: { formatter: false },
       })
-    } finally {
-      Formatter.gofmt.extensions = one.extensions
-      Formatter.gofmt.enabled = one.enabled
-      Formatter.gofmt.command = one.command
-      Formatter.mix.extensions = two.extensions
-      Formatter.mix.enabled = two.enabled
-      Formatter.mix.command = two.command
-    }
+      const b = yield* provideTmpdirInstance(() => Format.Service.use((fmt) => fmt.status()))
 
-    expect(max).toBe(2)
-  })
+      expect(a).toEqual([])
+      expect(b.length).toBeGreaterThan(0)
+    }),
+  )
 
-  test("runs matching formatters sequentially for the same file", async () => {
-    await using tmp = await tmpdir({
-      config: {
-        formatter: {
-          first: {
-            command: ["sh", "-c", 'sleep 0.05; v=$(cat "$1"); printf \'%sA\' "$v" > "$1"', "sh", "$FILE"],
-            extensions: [".seq"],
-          },
-          second: {
-            command: ["sh", "-c", 'v=$(cat "$1"); printf \'%sB\' "$v" > "$1"', "sh", "$FILE"],
-            extensions: [".seq"],
+  it.effect("runs enabled checks for matching formatters in parallel", () =>
+    provideTmpdirInstance((path) =>
+      Effect.gen(function* () {
+        const file = `${path}/test.parallel`
+        yield* Effect.promise(() => Bun.write(file, "x"))
+
+        const one = {
+          extensions: Formatter.gofmt.extensions,
+          enabled: Formatter.gofmt.enabled,
+          command: Formatter.gofmt.command,
+        }
+        const two = {
+          extensions: Formatter.mix.extensions,
+          enabled: Formatter.mix.enabled,
+          command: Formatter.mix.command,
+        }
+
+        let active = 0
+        let max = 0
+
+        yield* Effect.acquireUseRelease(
+          Effect.sync(() => {
+            Formatter.gofmt.extensions = [".parallel"]
+            Formatter.mix.extensions = [".parallel"]
+            Formatter.gofmt.command = ["sh", "-c", "true"]
+            Formatter.mix.command = ["sh", "-c", "true"]
+            Formatter.gofmt.enabled = async () => {
+              active++
+              max = Math.max(max, active)
+              await Bun.sleep(20)
+              active--
+              return true
+            }
+            Formatter.mix.enabled = async () => {
+              active++
+              max = Math.max(max, active)
+              await Bun.sleep(20)
+              active--
+              return true
+            }
+          }),
+          () =>
+            Format.Service.use((fmt) =>
+              Effect.gen(function* () {
+                yield* fmt.init()
+                yield* fmt.file(file)
+              }),
+            ),
+          () =>
+            Effect.sync(() => {
+              Formatter.gofmt.extensions = one.extensions
+              Formatter.gofmt.enabled = one.enabled
+              Formatter.gofmt.command = one.command
+              Formatter.mix.extensions = two.extensions
+              Formatter.mix.enabled = two.enabled
+              Formatter.mix.command = two.command
+            }),
+        )
+
+        expect(max).toBe(2)
+      }),
+    ),
+  )
+
+  it.effect("runs matching formatters sequentially for the same file", () =>
+    provideTmpdirInstance(
+      (path) =>
+        Effect.gen(function* () {
+          const file = `${path}/test.seq`
+          yield* Effect.promise(() => Bun.write(file, "x"))
+
+          yield* Format.Service.use((fmt) =>
+            Effect.gen(function* () {
+              yield* fmt.init()
+              yield* fmt.file(file)
+            }),
+          )
+
+          expect(yield* Effect.promise(() => Bun.file(file).text())).toBe("xAB")
+        }),
+      {
+        config: {
+          formatter: {
+            first: {
+              command: ["sh", "-c", 'sleep 0.05; v=$(cat "$1"); printf \'%sA\' "$v" > "$1"', "sh", "$FILE"],
+              extensions: [".seq"],
+            },
+            second: {
+              command: ["sh", "-c", 'v=$(cat "$1"); printf \'%sB\' "$v" > "$1"', "sh", "$FILE"],
+              extensions: [".seq"],
+            },
           },
         },
       },
-    })
-
-    const file = `${tmp.path}/test.seq`
-    await Bun.write(file, "x")
-
-    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)))
-    })
-
-    expect(await Bun.file(file).text()).toBe("xAB")
-  })
+    ),
+  )
 })