diff --git a/src/__tests__/engine-happy-path.test.ts b/src/__tests__/engine-happy-path.test.ts
index 6290d5f..8fa0a8f 100644
--- a/src/__tests__/engine-happy-path.test.ts
+++ b/src/__tests__/engine-happy-path.test.ts
@@ -49,10 +49,12 @@ import {
   mockDetectMatchedRuleSequence,
   createTestTmpDir,
   applyDefaultMocks,
+  cleanupPieceEngine,
 } from './engine-test-helpers.js';
 
 describe('PieceEngine Integration: Happy Path', () => {
   let tmpDir: string;
+  let engine: PieceEngine | null = null;
 
   beforeEach(() => {
     vi.resetAllMocks();
@@ -61,6 +63,10 @@ describe('PieceEngine Integration: Happy Path', () => {
   });
 
   afterEach(() => {
+    if (engine) {
+      cleanupPieceEngine(engine);
+      engine = null;
+    }
     if (existsSync(tmpDir)) {
       rmSync(tmpDir, { recursive: true, force: true });
     }
@@ -72,7 +78,7 @@ describe('PieceEngine Integration: Happy Path', () => {
   describe('Happy path', () => {
     it('should complete: plan → implement → ai_review → reviewers(all approved) → supervise → COMPLETE', async () => {
       const config = buildDefaultPieceConfig();
-      const engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
+      engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
 
       mockRunAgentSequence([
         makeResponse({ agent: 'plan', content: 'Plan complete' }),
@@ -111,7 +117,7 @@ describe('PieceEngine Integration: Happy Path', () => {
   describe('Review reject and fix loop', () => {
     it('should handle: reviewers(needs_fix) → fix → reviewers(all approved) → supervise → COMPLETE', async () => {
       const config = buildDefaultPieceConfig();
-      const engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
+      engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
 
       mockRunAgentSequence([
         makeResponse({ agent: 'plan', content: 'Plan done' }),
@@ -152,7 +158,7 @@ describe('PieceEngine Integration: Happy Path', () => {
 
     it('should inject latest reviewers output as Previous Response for repeated fix steps', async () => {
       const config = buildDefaultPieceConfig();
-      const engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
+      engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
 
       mockRunAgentSequence([
         makeResponse({ agent: 'plan', content: 'Plan done' }),
@@ -221,7 +227,7 @@ describe('PieceEngine Integration: Happy Path', () => {
 
     it('should use the latest movement output across different steps for Previous Response', async () => {
       const config = buildDefaultPieceConfig();
-      const engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
+      engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
 
       mockRunAgentSequence([
         makeResponse({ agent: 'plan', content: 'Plan done' }),
@@ -279,7 +285,7 @@ describe('PieceEngine Integration: Happy Path', () => {
   describe('AI review reject and fix', () => {
     it('should handle: ai_review(issues) → ai_fix → reviewers → supervise → COMPLETE', async () => {
       const config = buildDefaultPieceConfig();
-      const engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
+      engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
 
       mockRunAgentSequence([
         makeResponse({ agent: 'plan', content: 'Plan done' }),
@@ -316,7 +322,7 @@ describe('PieceEngine Integration: Happy Path', () => {
   describe('ABORT transition', () => {
     it('should abort when movement transitions to ABORT', async () => {
       const config = buildDefaultPieceConfig();
-      const engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
+      engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
 
       mockRunAgentSequence([
         makeResponse({ agent: 'plan', content: 'Requirements unclear' }),
@@ -343,7 +349,7 @@ describe('PieceEngine Integration: Happy Path', () => {
   describe('Event emissions', () => {
     it('should emit movement:start and movement:complete for each movement', async () => {
       const config = buildDefaultPieceConfig();
-      const engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
+      engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
 
       mockRunAgentSequence([
         makeResponse({ agent: 'plan', content: 'Plan' }),
@@ -390,7 +396,7 @@ describe('PieceEngine Integration: Happy Path', () => {
           }),
         ],
       };
-      const engine = new PieceEngine(simpleConfig, tmpDir, 'test task', { projectCwd: tmpDir });
+      engine = new PieceEngine(simpleConfig, tmpDir, 'test task', { projectCwd: tmpDir });
 
       mockRunAgentSequence([
         makeResponse({ agent: 'plan', content: 'Plan done' }),
@@ -413,7 +419,7 @@ describe('PieceEngine Integration: Happy Path', () => {
 
     it('should pass empty instruction to movement:start for parallel movements', async () => {
       const config = buildDefaultPieceConfig();
-      const engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
+      engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
 
       mockRunAgentSequence([
         makeResponse({ agent: 'plan', content: 'Plan' }),
@@ -451,7 +457,7 @@ describe('PieceEngine Integration: Happy Path', () => {
 
     it('should emit iteration:limit when max iterations reached', async () => {
       const config = buildDefaultPieceConfig({ maxIterations: 1 });
-      const engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
+      engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
 
       mockRunAgentSequence([
         makeResponse({ agent: 'plan', content: 'Plan' }),
@@ -475,7 +481,7 @@ describe('PieceEngine Integration: Happy Path', () => {
   describe('Movement output tracking', () => {
     it('should store outputs for all executed movements', async () => {
       const config = buildDefaultPieceConfig();
-      const engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
+      engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
 
       mockRunAgentSequence([
         makeResponse({ agent: 'plan', content: 'Plan output' }),
@@ -520,7 +526,7 @@ describe('PieceEngine Integration: Happy Path', () => {
           }),
         ],
       };
-      const engine = new PieceEngine(simpleConfig, tmpDir, 'test task', { projectCwd: tmpDir });
+      engine = new PieceEngine(simpleConfig, tmpDir, 'test task', { projectCwd: tmpDir });
 
       mockRunAgentSequence([
         makeResponse({ agent: 'plan', content: 'Plan done' }),
@@ -548,7 +554,7 @@ describe('PieceEngine Integration: Happy Path', () => {
 
     it('should emit phase events for all movements in happy path', async () => {
       const config = buildDefaultPieceConfig();
-      const engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
+      engine = new PieceEngine(config, tmpDir, 'test task', { projectCwd: tmpDir });
 
       mockRunAgentSequence([
         makeResponse({ agent: 'plan', content: 'Plan' }),
diff --git a/src/__tests__/engine-test-helpers.ts b/src/__tests__/engine-test-helpers.ts
index 5e3b7c5..4abd871 100644
--- a/src/__tests__/engine-test-helpers.ts
+++ b/src/__tests__/engine-test-helpers.ts
@@ -173,3 +173,13 @@ export function applyDefaultMocks(): void {
   vi.mocked(runStatusJudgmentPhase).mockResolvedValue('');
   vi.mocked(generateReportDir).mockReturnValue('test-report-dir');
 }
+
+/**
+ * Clean up PieceEngine instances to prevent EventEmitter memory leaks.
+ * Call this in afterEach to ensure all event listeners are removed.
+ */
+export function cleanupPieceEngine(engine: any): void {
+  if (engine && typeof engine.removeAllListeners === 'function') {
+    engine.removeAllListeners();
+  }
+}
diff --git a/src/__tests__/watcher.test.ts b/src/__tests__/watcher.test.ts
index 4b48e19..601e33c 100644
--- a/src/__tests__/watcher.test.ts
+++ b/src/__tests__/watcher.test.ts
@@ -10,6 +10,7 @@ import type { TaskInfo } from '../infra/task/types.js';
 
 describe('TaskWatcher', () => {
   const testDir = `/tmp/takt-watcher-test-${Date.now()}`;
+  let watcher: TaskWatcher | null = null;
 
   beforeEach(() => {
     mkdirSync(join(testDir, '.takt', 'tasks'), { recursive: true });
@@ -17,6 +18,11 @@ describe('TaskWatcher', () => {
   });
 
   afterEach(() => {
+    // Ensure watcher is stopped before cleanup
+    if (watcher) {
+      watcher.stop();
+      watcher = null;
+    }
     if (existsSync(testDir)) {
       rmSync(testDir, { recursive: true, force: true });
     }
@@ -24,19 +30,19 @@ describe('TaskWatcher', () => {
 
   describe('constructor', () => {
     it('should create watcher with default options', () => {
-      const watcher = new TaskWatcher(testDir);
+      watcher = new TaskWatcher(testDir);
       expect(watcher.isRunning()).toBe(false);
     });
 
     it('should accept custom poll interval', () => {
-      const watcher = new TaskWatcher(testDir, { pollInterval: 500 });
+      watcher = new TaskWatcher(testDir, { pollInterval: 500 });
       expect(watcher.isRunning()).toBe(false);
     });
   });
 
   describe('watch', () => {
     it('should detect and process a task file', async () => {
-      const watcher = new TaskWatcher(testDir, { pollInterval: 50 });
+      watcher = new TaskWatcher(testDir, { pollInterval: 50 });
       const processed: string[] = [];
 
       // Pre-create a task file
@@ -59,7 +65,7 @@ describe('TaskWatcher', () => {
     });
 
     it('should wait when no tasks are available', async () => {
-      const watcher = new TaskWatcher(testDir, { pollInterval: 50 });
+      watcher = new TaskWatcher(testDir, { pollInterval: 50 });
       let pollCount = 0;
 
       // Start watching, add a task after a delay
@@ -81,7 +87,7 @@ describe('TaskWatcher', () => {
     });
 
     it('should process multiple tasks sequentially', async () => {
-      const watcher = new TaskWatcher(testDir, { pollInterval: 50 });
+      watcher = new TaskWatcher(testDir, { pollInterval: 50 });
       const processed: string[] = [];
 
       // Pre-create two task files
@@ -111,7 +117,7 @@ describe('TaskWatcher', () => {
 
   describe('stop', () => {
     it('should stop the watcher gracefully', async () => {
-      const watcher = new TaskWatcher(testDir, { pollInterval: 50 });
+      watcher = new TaskWatcher(testDir, { pollInterval: 50 });
 
       // Start watching, stop after a short delay
       const watchPromise = watcher.watch(async () => {
@@ -127,7 +133,7 @@ describe('TaskWatcher', () => {
     });
 
     it('should abort sleep immediately when stopped', async () => {
-      const watcher = new TaskWatcher(testDir, { pollInterval: 10000 });
+      watcher = new TaskWatcher(testDir, { pollInterval: 10000 });
 
       const start = Date.now();
       const watchPromise = watcher.watch(async () => {});
diff --git a/vitest.config.ts b/vitest.config.ts
index a05b87a..c100b89 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -5,6 +5,17 @@ export default defineConfig({
     include: ['src/__tests__/**/*.test.ts'],
     environment: 'node',
     globals: false,
+    // Ensure proper cleanup by forcing sequential execution and graceful shutdown
+    pool: 'threads',
+    poolOptions: {
+      threads: {
+        singleThread: true,
+      },
+    },
+    // Increase timeout for tests with async cleanup
+    testTimeout: 15000,
+    // Force exit after tests complete to prevent hanging
+    teardownTimeout: 5000,
     coverage: {
       provider: 'v8',
       reporter: ['text', 'json', 'html'],