update worker manager and worker to support plugin registry

PluginCore/backend_registry.py

@@ -6,6 +6,7 @@ Backends are discovered from their owning plugins and instantiated from config.
 from __future__ import annotations
 
 import importlib
+import importlib.util
 import inspect
 import re
 from typing import Any, Dict, Optional, Type
@@ -119,6 +120,16 @@ def _discover_plugin_backend_class(backend_type: str) -> Optional[Type[BackendBa
     return resolved
 
 
+def _plugin_module_exists(plugin_name: str) -> bool:
+    normalized = _normalize_backend_type(plugin_name)
+    if not normalized:
+        return False
+    try:
+        return importlib.util.find_spec(f"plugins.{normalized}") is not None
+    except Exception:
+        return False
+
+
 def _resolve_backend_class(backend_type: str) -> Optional[Type[BackendBase]]:
     normalized = _normalize_backend_type(backend_type)
     if not normalized:
@@ -200,7 +211,11 @@ class BackendRegistry:
                 continue
             backend_cls = _resolve_backend_class(backend_type)
             if backend_cls is None:
-                if backend_type not in _PROVIDER_ONLY_BACKEND_NAMES and not self._suppress_debug:
+                if (
+                    backend_type not in _PROVIDER_ONLY_BACKEND_NAMES
+                    and not self._suppress_debug
+                    and not _plugin_module_exists(backend_type)
+                ):
                     debug(f"[BackendRegistry] Unknown backend type '{raw_backend_type}'")
                 continue