fix(os): normalize Windows drive-root paths for fs.watch

packages/agent-core-v2/src/os/backends/node-local/hostFsWatchService.ts

@@ -3,6 +3,8 @@
  *
  * Reports precise or coarse host filesystem changes through platform
  * watchers. Each handle owns and disposes its watcher. Bound at App scope.
+ * On Windows, drive-root watch paths such as `D:` / `/D:` are normalized to
+ * `D:\` before `fs.watch`, avoiding ENOENT when the process CWD is a drive root.
  */
 
 import { watch as fsWatch } from 'node:fs';
@@ -237,13 +239,23 @@ export class HostFsWatchService implements IHostFsWatchService {
   constructor(private readonly runtime: HostFsWatchRuntime = NODE_HOST_FS_WATCH_RUNTIME) {}
 
   watch(path: string, options?: HostFsWatchOptions): IHostFsWatchHandle {
+    const root = normalizeWatchRoot(path, this.runtime.platform);
     if (useNativeRecursive(options, this.runtime.platform)) {
-      return new SignalWatchHandle(path, options, this.runtime);
+      return new SignalWatchHandle(root, options, this.runtime);
     }
-    return new HostFsWatchHandle(path, options);
+    return new HostFsWatchHandle(root, options);
   }
 }
 
+function normalizeWatchRoot(path: string, platform: NodeJS.Platform): string {
+  if (platform !== 'win32') return path;
+  const driveOnly = path.match(/^\/?([A-Za-z]):\/?$/);
+  if (driveOnly) {
+    return `${driveOnly[1].toUpperCase()}:\\`;
+  }
+  return path;
+}
+
 function useNativeRecursive(
   options: HostFsWatchOptions | undefined,
   platform: NodeJS.Platform,

packages/agent-core-v2/test/os/backends/node-local/hostFsWatchService.test.ts

@@ -298,6 +298,26 @@ describe('host filesystem change notifications', () => {
     expect(events).toHaveLength(0);
   });
 
+
+  it('normalizes Windows drive-root watch paths before calling watchNative', () => {
+    const watched: string[] = [];
+    const runtime: HostFsWatchRuntime = {
+      platform: 'win32',
+      watchNative: (root, _listener) => {
+        watched.push(root);
+        return new TestNativeWatcher();
+      },
+      scheduleRetry: () => ({ dispose: () => undefined }),
+    };
+    const service = new HostFsWatchService(runtime);
+    handle = service.watch('/D:', { signal: true });
+    expect(watched).toEqual(['D:\\']);
+    handle.dispose();
+    handle = undefined;
+
+    handle = service.watch('E:', { signal: true });
+    expect(watched).toEqual(['D:\\', 'E:\\']);
+  });
   it.skipIf(process.platform !== 'darwin')(
     'signal mode keeps the fd footprint bounded on a fat subtree',
     async () => {