Fix plugin list bug and switch watcher to PollingObserver

- Fix: list_plugins imported _REGISTRY as a direct reference to the
  empty list that existed at import time; register_services() replaces
  _REGISTRY with a new list so the imported reference was always [].
  Added get_registry() helper so callers access the live list via the
  module namespace. GET /api/plugins now correctly returns accessible
  plugins for the current user.

- Fix: switch watchdog from InotifyObserver to PollingObserver. Inotify
  events from the macOS host are not forwarded through the Docker bind
  mount, so new files were only detected via the startup scan. PollingObserver
  (1s default interval) works reliably on all platforms including
  macOS+Docker bind mounts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/routers/plugins.py

@@ -20,7 +20,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from app.database import get_db
 from app.deps import check_plugin_access, get_current_user
 from app.models.user import User
-from app.services.service_health import _REGISTRY, get_cached_manifest, get_service_url
+from app.services.service_health import get_cached_manifest, get_registry, get_service_url
 
 router = APIRouter()
 
@@ -72,7 +72,7 @@ async def list_plugins(
 ) -> list[dict]:
     """Return the list of plugins the current user may access."""
     accessible = []
-    for svc in _REGISTRY:
+    for svc in get_registry():
         manifest = get_cached_manifest(svc.id)
         if manifest is None:
             continue

backend/app/services/service_health.py

@@ -162,3 +162,8 @@ def get_service_url(service_id: str) -> str | None:
         if svc.id == service_id:
             return svc.internal_url
     return None
+
+
+def get_registry() -> list[ServiceDefinition]:
+    """Return the current service registry (always up-to-date after register_services)."""
+    return _REGISTRY

features/doc-service/app/services/file_watcher.py

@@ -25,7 +25,7 @@ import uuid
 from pathlib import Path
 
 from watchdog.events import FileSystemEventHandler
-from watchdog.observers import Observer
+from watchdog.observers.polling import PollingObserver
 
 from app.database import AsyncSessionLocal
 from app.models.category import DocumentCategory
@@ -226,7 +226,7 @@ class FileWatcherService:
             return
 
         handler = _PdfEventHandler(self._watch_root, self._loop, config)
-        self._observer = Observer()
+        self._observer = PollingObserver()
         self._observer.schedule(handler, watch_path, recursive=True)
         self._observer.start()
         logger.info("[watcher] started, watching %s", watch_path)