Refactor backend integration and service architecture

- Removed the backend client compatibility wrapper and associated methods to streamline backend integration.
- Updated session management to utilize control plane gateways and runtime configuration providers.
- Adjusted TTS service implementations to remove the EdgeTTS service and simplify service dependencies.
- Enhanced documentation to reflect changes in backend integration and service architecture.
- Updated configuration files to remove deprecated TTS provider options and clarify available settings.

engine/core/session.py

@@ -11,6 +11,13 @@ from loguru import logger
 
 from app.backend_adapters import build_backend_adapter_from_settings
 from core.transports import BaseTransport
+from core.ports import (
+    AssistantRuntimeConfigProvider,
+    ControlPlaneGateway,
+    ConversationHistoryStore,
+    KnowledgeRetriever,
+    ToolCatalog,
+)
 from core.duplex_pipeline import DuplexPipeline
 from core.conversation import ConversationTurn
 from core.history_bridge import SessionHistoryBridge
@@ -97,7 +104,11 @@ class Session:
         session_id: str,
         transport: BaseTransport,
         use_duplex: bool = None,
-        backend_gateway: Optional[Any] = None,
+        control_plane_gateway: Optional[ControlPlaneGateway] = None,
+        runtime_config_provider: Optional[AssistantRuntimeConfigProvider] = None,
+        history_store: Optional[ConversationHistoryStore] = None,
+        knowledge_retriever: Optional[KnowledgeRetriever] = None,
+        tool_catalog: Optional[ToolCatalog] = None,
         assistant_id: Optional[str] = None,
     ):
         """
@@ -107,15 +118,24 @@ class Session:
             session_id: Unique session identifier
             transport: Transport instance for communication
             use_duplex: Whether to use duplex pipeline (defaults to settings.duplex_enabled)
+            control_plane_gateway: Optional composite control-plane dependency
+            runtime_config_provider: Optional assistant runtime config provider
+            history_store: Optional conversation history store
+            knowledge_retriever: Optional knowledge retrieval dependency
+            tool_catalog: Optional tool resource catalog
         """
         self.id = session_id
         self.transport = transport
         self.use_duplex = use_duplex if use_duplex is not None else settings.duplex_enabled
         self.audio_frame_bytes = self._compute_audio_frame_bytes()
         self._assistant_id = str(assistant_id or "").strip() or None
-        self._backend_gateway = backend_gateway or build_backend_adapter_from_settings()
+        self._control_plane_gateway = control_plane_gateway or build_backend_adapter_from_settings()
+        self._runtime_config_provider = runtime_config_provider or self._control_plane_gateway
+        self._history_store = history_store or self._control_plane_gateway
+        self._knowledge_retriever = knowledge_retriever or self._control_plane_gateway
+        self._tool_catalog = tool_catalog or self._control_plane_gateway
         self._history_bridge = SessionHistoryBridge(
-            history_writer=self._backend_gateway,
+            history_writer=self._history_store,
             enabled=settings.history_enabled,
             queue_max_size=settings.history_queue_max_size,
             retry_max_attempts=settings.history_retry_max_attempts,
@@ -128,8 +148,8 @@ class Session:
             session_id=session_id,
             system_prompt=settings.duplex_system_prompt,
             greeting=settings.duplex_greeting,
-            knowledge_searcher=getattr(self._backend_gateway, "search_knowledge_context", None),
-            tool_resource_resolver=getattr(self._backend_gateway, "fetch_tool_resource", None),
+            knowledge_searcher=getattr(self._knowledge_retriever, "search_knowledge_context", None),
+            tool_resource_resolver=getattr(self._tool_catalog, "fetch_tool_resource", None),
         )
 
         # Session state
@@ -935,18 +955,18 @@ class Session:
         self,
         assistant_id: str,
     ) -> tuple[Dict[str, Any], Optional[Dict[str, str]]]:
-        """Load trusted runtime metadata from backend assistant config."""
+        """Load trusted runtime metadata from control-plane assistant config."""
         if not assistant_id:
             return {}, {
                 "code": "protocol.assistant_id_required",
                 "message": "Missing required query parameter assistant_id",
             }
 
-        provider = getattr(self._backend_gateway, "fetch_assistant_config", None)
+        provider = getattr(self._runtime_config_provider, "fetch_assistant_config", None)
         if not callable(provider):
             return {}, {
                 "code": "assistant.config_unavailable",
-                "message": "Assistant config backend unavailable",
+                "message": "Assistant config control plane unavailable",
             }
 
         payload = await provider(str(assistant_id).strip())