diff --git a/tests/unit/main/watcher/FileWatcher.test.ts b/tests/unit/main/watcher/FileWatcher.test.ts
new file mode 100644
index 0000000000..2323e50ef3
--- /dev/null
+++ b/tests/unit/main/watcher/FileWatcher.test.ts
@@ -0,0 +1,128 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
+import path from 'path'
+import { FileWatcher } from '../../../../src/main/watcher/FileWatcher'
+import { IPC_CHANNELS } from '../../../../src/shared/ipc-channels'
+import * as git from '../../../../src/main/utils/git'
+import * as fs from 'fs'
+
+type WatchRecord = {
+  path: string
+  listener?: (eventType: string, filename?: string) => void
+  handlers: Record<string, Array<(error: Error) => void>>
+  close: ReturnType<typeof vi.fn>
+}
+
+const watchRecords: WatchRecord[] = []
+
+vi.mock('fs', () => {
+  const watch = vi.fn(
+    (watchedPath: string, optionsOrListener: unknown, maybeListener?: unknown) => {
+      const listener =
+        typeof optionsOrListener === 'function'
+          ? (optionsOrListener as (eventType: string, filename?: string) => void)
+          : (maybeListener as (eventType: string, filename?: string) => void)
+
+      const record: WatchRecord = {
+        path: watchedPath,
+        listener,
+        handlers: {},
+        close: vi.fn()
+      }
+
+      watchRecords.push(record)
+
+      return {
+        on: vi.fn((event: string, handler: (error: Error) => void) => {
+          if (!record.handlers[event]) {
+            record.handlers[event] = []
+          }
+          record.handlers[event].push(handler)
+          return undefined
+        }),
+        close: record.close
+      }
+    }
+  )
+
+  return {
+    watch,
+    existsSync: vi.fn(() => true)
+  }
+})
+
+vi.mock('../../../../src/main/utils/git', () => ({
+  getGitHeadPath: vi.fn()
+}))
+
+describe('FileWatcher', () => {
+  beforeEach(() => {
+    vi.useFakeTimers()
+    vi.clearAllMocks()
+    watchRecords.length = 0
+  })
+
+  afterEach(() => {
+    vi.useRealTimers()
+  })
+
+  it('watches git HEAD and notifies renderer on changes', () => {
+    const headPath = '/repo/.git/HEAD'
+    vi.mocked(git.getGitHeadPath).mockReturnValue(headPath)
+
+    const send = vi.fn()
+    const mainWindow = {
+      isDestroyed: () => false,
+      webContents: { send }
+    }
+
+    const watcher = new FileWatcher({
+      debounceMs: 0,
+      getMainWindow: () => mainWindow
+    })
+
+    watcher.watch('session-1', '/repo')
+
+    expect(fs.watch).toHaveBeenCalledWith('/repo', { recursive: true }, expect.any(Function))
+    expect(fs.watch).toHaveBeenCalledWith(headPath, expect.any(Function))
+
+    const headRecord = watchRecords.find((record) => record.path === headPath)
+    expect(headRecord?.listener).toBeDefined()
+
+    headRecord?.listener?.('change')
+    vi.runAllTimers()
+
+    expect(send).toHaveBeenCalledWith(IPC_CHANNELS.FS_FILE_CHANGED, {
+      directory: path.dirname(headPath),
+      eventType: 'change',
+      path: headPath,
+      sessionIds: ['session-1']
+    })
+  })
+
+  it('closes git HEAD watcher after last session unwatch', () => {
+    const headPath = '/repo/.git/HEAD'
+    vi.mocked(git.getGitHeadPath).mockReturnValue(headPath)
+
+    const mainWindow = {
+      isDestroyed: () => false,
+      webContents: { send: vi.fn() }
+    }
+
+    const watcher = new FileWatcher({
+      debounceMs: 0,
+      getMainWindow: () => mainWindow
+    })
+
+    watcher.watch('session-1', '/repo')
+    watcher.watch('session-2', '/repo')
+
+    const headRecord = watchRecords.find((record) => record.path === headPath)
+    expect(headRecord).toBeDefined()
+
+    watcher.unwatch('session-1')
+    expect(headRecord?.close).not.toHaveBeenCalled()
+
+    watcher.unwatch('session-2')
+    expect(headRecord?.close).toHaveBeenCalledTimes(1)
+  })
+})