feat(plugin): add unrestricted knowledge base query handlers

Add handlers for LIST_KNOWLEDGE_BASES and RETRIEVE_KNOWLEDGE actions
that allow plugins to list and retrieve from any knowledge base without
pipeline scope restrictions, complementing the existing pipeline-scoped handlers.

src/langbot/pkg/plugin/handler.py

@@ -613,6 +613,47 @@ class RuntimeConnectionHandler(handler.Handler):
 
         # ================= Knowledge Base Query APIs =================
 
+        @self.action(PluginToRuntimeAction.LIST_KNOWLEDGE_BASES)
+        async def list_knowledge_bases(data: dict[str, Any]) -> handler.ActionResponse:
+            """List all knowledge bases available in the LangBot instance (unrestricted)."""
+            knowledge_bases = []
+            for kb_uuid, kb in self.ap.rag_mgr.knowledge_bases.items():
+                knowledge_bases.append(
+                    {
+                        'uuid': kb.get_uuid(),
+                        'name': kb.get_name(),
+                        'description': kb.knowledge_base_entity.description or '',
+                    }
+                )
+            return handler.ActionResponse.success(data={'knowledge_bases': knowledge_bases})
+
+        @self.action(PluginToRuntimeAction.RETRIEVE_KNOWLEDGE)
+        async def retrieve_knowledge(data: dict[str, Any]) -> handler.ActionResponse:
+            """Retrieve documents from any knowledge base (unrestricted)."""
+            kb_id = data['kb_id']
+            query_text = data['query_text']
+            top_k = data.get('top_k', 5)
+            filters = data.get('filters', {})
+
+            kb = await self.ap.rag_mgr.get_knowledge_base_by_uuid(kb_id)
+            if not kb:
+                return handler.ActionResponse.error(
+                    message=f'Knowledge base {kb_id} not found',
+                )
+
+            try:
+                entries = await kb.retrieve(
+                    query_text,
+                    settings={
+                        'top_k': top_k,
+                        'filters': filters,
+                    },
+                )
+                results = [entry.model_dump(mode='json') for entry in entries]
+                return handler.ActionResponse.success(data={'results': results})
+            except Exception as e:
+                return _make_rag_error_response(e, 'RetrievalError', kb_id=kb_id)
+
         @self.action(PluginToRuntimeAction.LIST_PIPELINE_KNOWLEDGE_BASES)
         async def list_pipeline_knowledge_bases(data: dict[str, Any]) -> handler.ActionResponse:
             """List knowledge bases configured for the current query's pipeline."""