diff --git a/.gitignore b/.gitignore
index d69f5ad..fccd5dd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -209,4 +209,5 @@ dist-web
 .history
 .ionide
 
-# End of https://www.toptal.com/developers/gitignore/api/macos,git,visualstudiocode,node
\ No newline at end of file
+# End of https://www.toptal.com/developers/gitignore/api/macos,git,visualstudiocode,node
+.gstack/
diff --git a/src/main/__tests__/watcher.test.ts b/src/main/__tests__/watcher.test.ts
new file mode 100644
index 0000000..ffc8eb7
--- /dev/null
+++ b/src/main/__tests__/watcher.test.ts
@@ -0,0 +1,103 @@
+import { EventEmitter } from 'events';
+import { vi, describe, it, expect, beforeEach, afterEach } from 'vitest';
+
+vi.mock('chokidar');
+vi.mock('electron', () => ({ BrowserWindow: { getAllWindows: () => [] } }));
+
+const mockAppendUndoEntries = vi.fn().mockResolvedValue(undefined);
+vi.mock('../store', () => ({ appendUndoEntries: mockAppendUndoEntries }));
+
+const mockQueueRenamedNotification = vi.fn().mockResolvedValue(undefined);
+vi.mock('../notifier', () => ({
+  queueRenamedNotification: mockQueueRenamedNotification,
+  notifyManualQueue: vi.fn().mockResolvedValue(undefined),
+}));
+
+vi.mock('../nanoid', () => ({ nanoid: () => 'test-id' }));
+
+const mockNormalizeEntry = vi.fn();
+vi.mock('../../core/normalizer', () => ({ normalizeEntry: mockNormalizeEntry }));
+
+import chokidar from 'chokidar';
+import type { WatchedDir } from '../../core/types';
+
+// 테스트마다 고유 경로를 사용해 모듈 레벨 recentlyRenamed 상태 충돌 방지
+function makePaths(slug: string) {
+  const nfc = `/test/watch/${slug}.txt`;
+  return { nfc, nfd: nfc.normalize('NFD') };
+}
+
+function makeDir(id: string): WatchedDir {
+  return { id, path: '/test/watch', recursive: false, mode: 'auto', enabled: true, customRanges: [] };
+}
+
+describe('watcher — in-flight race condition', () => {
+  let mockWatcher: EventEmitter & { close: ReturnType<typeof vi.fn> };
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockWatcher = Object.assign(new EventEmitter(), { close: vi.fn().mockResolvedValue(undefined) });
+    vi.mocked(chokidar.watch).mockReturnValue(mockWatcher as unknown as ReturnType<typeof chokidar.watch>);
+  });
+
+  afterEach(async () => {
+    const { stopDir } = await import('../watcher');
+    // 각 테스트에서 사용한 id 정리
+    for (const id of ['dir-burst', 'dir-nfc-reentry', 'dir-nfd-reentry']) {
+      await stopDir(id);
+    }
+  });
+
+  it('동일 NFD 경로에 burst add 이벤트가 와도 normalizeEntry가 1번만 호출된다', async () => {
+    const { nfc, nfd } = makePaths('강의자료-burst');
+    mockNormalizeEntry.mockResolvedValue({ type: 'file', status: 'renamed', oldPath: nfd, newPath: nfc });
+
+    const { startDir } = await import('../watcher');
+    await startDir(makeDir('dir-burst'));
+
+    // 같은 경로를 동기적으로 두 번 emit — race 시나리오 재현
+    mockWatcher.emit('add', nfd);
+    mockWatcher.emit('add', nfd);
+    await new Promise((r) => setTimeout(r, 0));
+
+    expect(mockNormalizeEntry).toHaveBeenCalledTimes(1);
+    expect(mockAppendUndoEntries).toHaveBeenCalledTimes(1);
+  });
+
+  it('rename 완료 후 NFC 경로로 다시 add 이벤트가 와도 recentlyRenamed 가드에 막힌다', async () => {
+    const { nfc, nfd } = makePaths('강의자료-nfc-reentry');
+    mockNormalizeEntry.mockResolvedValue({ type: 'file', status: 'renamed', oldPath: nfd, newPath: nfc });
+
+    const { startDir } = await import('../watcher');
+    await startDir(makeDir('dir-nfc-reentry'));
+
+    mockWatcher.emit('add', nfd);
+    await new Promise((r) => setTimeout(r, 0));
+    expect(mockNormalizeEntry).toHaveBeenCalledTimes(1);
+
+    vi.clearAllMocks();
+
+    // RENAME_TTL(2000ms) 이내에 NFC 경로로 재진입 — 가드에 막혀야 함
+    mockWatcher.emit('add', nfc);
+    await new Promise((r) => setTimeout(r, 0));
+    expect(mockNormalizeEntry).not.toHaveBeenCalled();
+  });
+
+  it('rename 완료 후 NFD 경로로 재진입해도 recentlyRenamed 가드에 막힌다', async () => {
+    const { nfc, nfd } = makePaths('강의자료-nfd-reentry');
+    mockNormalizeEntry.mockResolvedValue({ type: 'file', status: 'renamed', oldPath: nfd, newPath: nfc });
+
+    const { startDir } = await import('../watcher');
+    await startDir(makeDir('dir-nfd-reentry'));
+
+    mockWatcher.emit('add', nfd);
+    await new Promise((r) => setTimeout(r, 0));
+    expect(mockNormalizeEntry).toHaveBeenCalledTimes(1);
+
+    vi.clearAllMocks();
+
+    mockWatcher.emit('add', nfd);
+    await new Promise((r) => setTimeout(r, 0));
+    expect(mockNormalizeEntry).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/main/watcher.ts b/src/main/watcher.ts
index 38833a3..23185d6 100644
--- a/src/main/watcher.ts
+++ b/src/main/watcher.ts
@@ -12,6 +12,7 @@ type ActivityListener = (event: ActivityEvent) => void;
 
 const watchers = new Map<string, FSWatcher>();
 const recentlyRenamed = new Map<string, number>();
+const inFlight = new Set<string>();
 const RENAME_TTL = 2000;
 const listeners = new Set<ActivityListener>();
 const manualQueue = new Map<string, string[]>();
@@ -51,39 +52,51 @@ export async function startDir(dir: WatchedDir): Promise<void> {
     persistent: true,
     depth: dir.recursive ? undefined : 0,
     ignored: /(^|[/\\])\../,
+    awaitWriteFinish: { stabilityThreshold: 300, pollInterval: 100 },
   });
 
   async function handlePath(filePath: string, type: 'file' | 'directory'): Promise<void> {
     const now = Date.now();
-    const lastRenamed = recentlyRenamed.get(filePath);
+    const key = filePath.normalize('NFC');
+
+    // 동일 경로가 이미 처리 중이면 즉시 return (burst add 이벤트로 인한 race 차단)
+    if (inFlight.has(key)) return;
+    const lastRenamed = recentlyRenamed.get(key);
     if (lastRenamed && now - lastRenamed < RENAME_TTL) return;
 
     const basename = filePath.split('/').pop() ?? '';
     if (!shouldNormalize(basename, filterOpts)) return;
 
-    if (dir.mode === 'auto') {
-      const result = await normalizeEntry(filePath, type, filterOpts);
-      if (result.status === 'renamed' || result.status === 'noop-same-inode') {
-        recentlyRenamed.set(result.newPath, Date.now());
-        if (result.status === 'renamed') {
-          await store.appendUndoEntries([
-            { id: nanoid(), ts: now, oldPath: result.oldPath, newPath: result.newPath, reverted: false },
-          ]);
+    inFlight.add(key);
+    try {
+      if (dir.mode === 'auto') {
+        const result = await normalizeEntry(filePath, type, filterOpts);
+        if (result.status === 'renamed' || result.status === 'noop-same-inode') {
+          // oldPath와 newPath 모두 등록 — chokidar가 NFD/NFC 변형 중 어느 쪽으로 이벤트를 보내도 막힘
+          recentlyRenamed.set(result.oldPath.normalize('NFC'), Date.now());
+          recentlyRenamed.set(result.newPath.normalize('NFC'), Date.now());
+          if (result.status === 'renamed') {
+            await store.appendUndoEntries([
+              { id: nanoid(), ts: now, oldPath: result.oldPath, newPath: result.newPath, reverted: false },
+            ]);
+          }
+          emit({ type: 'rename', ts: now, dirId: dir.id, message: `${result.oldPath} → ${result.newPath}`, result });
+          // 알림은 배치로 처리 — 인터벌마다 총 건수 발송
+          await notifier.queueRenamedNotification(dir.path);
+        } else if (result.status === 'collision') {
+          emit({ type: 'collision', ts: now, dirId: dir.id, message: `충돌: ${result.oldPath}`, result });
         }
-        emit({ type: 'rename', ts: now, dirId: dir.id, message: `${result.oldPath} → ${result.newPath}`, result });
-        // 알림은 배치로 처리 — 인터벌마다 총 건수 발송
-        await notifier.queueRenamedNotification(dir.path);
-      } else if (result.status === 'collision') {
-        emit({ type: 'collision', ts: now, dirId: dir.id, message: `충돌: ${result.oldPath}`, result });
+      } else {
+        const queue = manualQueue.get(dir.id) ?? [];
+        if (!queue.includes(filePath)) {
+          queue.push(filePath);
+          manualQueue.set(dir.id, queue);
+          emit({ type: 'info', ts: now, dirId: dir.id, message: `수동 대기: ${filePath}` });
+        }
+        await notifier.notifyManualQueue(queue.length, dir.path);
       }
-    } else {
-      const queue = manualQueue.get(dir.id) ?? [];
-      if (!queue.includes(filePath)) {
-        queue.push(filePath);
-        manualQueue.set(dir.id, queue);
-        emit({ type: 'info', ts: now, dirId: dir.id, message: `수동 대기: ${filePath}` });
-      }
-      await notifier.notifyManualQueue(queue.length, dir.path);
+    } finally {
+      inFlight.delete(key);
     }
   }
 
@@ -147,7 +160,8 @@ export async function applyManualQueue(dirId: string, dir: WatchedDir): Promise<
       const result = await normalizeEntry(filePath, type, filterOpts);
       results.push(result);
       if (result.status === 'renamed') {
-        recentlyRenamed.set(result.newPath, Date.now());
+        recentlyRenamed.set(result.oldPath.normalize('NFC'), Date.now());
+        recentlyRenamed.set(result.newPath.normalize('NFC'), Date.now());
         undoEntries.push({ id: nanoid(), ts: now, oldPath: result.oldPath, newPath: result.newPath, reverted: false });
       }
     } catch (err) {