fix: fall back from WSL workspace watch failures

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: mussonking

apps/desktop/src/main/workspace-watcher.test.ts

@@ -161,15 +161,18 @@ describe('files-watcher subscribe / unsubscribe', () => {
     expect(__test.watchers.has('d1')).toBe(false);
   });
 
-  it('falls back to polling when native watch is denied by permissions', () => {
+  it.each([
+    ['permission denial', 'EPERM'],
+    ['unsupported directory watch', 'EISDIR'],
+  ])('falls back to polling when native watch fails from %s', (_reason, code) => {
     reset();
-    const err = Object.assign(new Error('operation not permitted'), { code: 'EPERM' });
+    const err = Object.assign(new Error('watch unavailable'), { code });
     watchMock.mockImplementation(() => {
       throw err;
     });
     getDesignMock.mockReturnValue({
       id: 'd1',
-      workspacePath: tempWorkspace('codesign-watch-eperm'),
+      workspacePath: tempWorkspace(`codesign-watch-${code.toLowerCase()}`),
     });
     registerFilesWatcherIpc({} as never, () => null);
     const sub = getHandler('codesign:files:v1:subscribe');

apps/desktop/src/main/workspace-watcher.ts

@@ -65,9 +65,9 @@ function toForwardSlashes(path: string): string {
   return sep === '/' ? path : path.split(sep).join('/');
 }
 
-function isPermissionWatchError(err: unknown): boolean {
+function shouldFallbackToPolling(err: unknown): boolean {
   const code = (err as NodeJS.ErrnoException).code;
-  return code === 'EPERM' || code === 'EACCES';
+  return code === 'EPERM' || code === 'EACCES' || code === 'EISDIR';
 }
 
 function isWorkspaceUnavailableWatchError(err: unknown): boolean {
@@ -183,7 +183,7 @@ function startWatcher(
       workspacePath,
       error: err instanceof Error ? err.message : String(err),
     });
-    if (isPermissionWatchError(err)) {
+    if (shouldFallbackToPolling(err)) {
       watchers.set(designId, entry);
       startPolling(designId, entry, getWin);
       return { ok: true, entry };
@@ -196,7 +196,7 @@ function startWatcher(
   entry.watcher = watcher;
   watcher.on('error', (err) => {
     log.warn('files.watch.error', { designId, error: String(err) });
-    if (!isPermissionWatchError(err)) return;
+    if (!shouldFallbackToPolling(err)) return;
     const active = watchers.get(designId);
     if (!active || active.watcher !== watcher) return;
     try {