Add on_client_ready method to BaseBrain and WorkflowBrain

- Implement on_client_ready in BaseBrain to handle client-visible state after the app message channel is ready.
- Extend WorkflowBrain with on_client_ready to replay state that may have been emitted before WebRTC data was ready.
- Update pipeline to call on_client_ready when a client connects.
- Enhance tests to verify the correct behavior of on_client_ready in WorkflowBrain.

backend/services/brains/base.py

@@ -86,6 +86,9 @@ class BaseBrain:
     async def on_connected(self) -> None:
         """Handle a connected client after the common greeting is queued."""
 
+    async def on_client_ready(self) -> None:
+        """Replay client-visible state after its app message channel is ready."""
+
     def record_user_message(self, content: str) -> None:
         """Observe a committed user message for brain-owned routing state."""
 
@@ -126,6 +129,8 @@ class Brain(Protocol):
 
     async def on_connected(self) -> None: ...
 
+    async def on_client_ready(self) -> None: ...
+
     def record_user_message(self, content: str) -> None: ...
 
     async def on_user_turn_end(self, content: str) -> bool: ...

backend/services/brains/workflow_brain.py

@@ -123,6 +123,19 @@ class WorkflowBrain(BaseBrain):
         await self._manager.initialize(node_config)
         logger.info(f"工作流模式启用: 当前节点={self._manager.current_node}")
 
+    async def on_client_ready(self) -> None:
+        """Replay state that may have been emitted before WebRTC data was ready."""
+        current_node = (
+            str(self._manager.current_node)
+            if self._manager and self._manager.current_node
+            else self._engine.start_id
+        )
+        await self._emit_node_active(current_node)
+        await self._emit_variables(
+            reason="client_ready",
+            node_id=current_node,
+        )
+
     def record_user_message(self, content: str) -> None:
         if content and not self._ended:
             self._store.record("user", content)

backend/services/pipecat/pipeline.py

@@ -1218,6 +1218,7 @@ async def run_pipeline(
         if greeting and not greeting_transcript_sent:
             greeting_transcript_sent = True
             await queue_transcript("assistant", greeting, time_now_iso8601())
+        await brain.on_client_ready()
 
     @transport.event_handler("on_client_connected")
     async def on_client_connected(_transport, _client):