feat: add session updates and message dialogs

backend/services/brains/workflow_brain.py

@@ -28,7 +28,12 @@ from pipecat.services.llm_service import (
     FunctionCallParams,
     FunctionCallResultProperties,
 )
-from services.brains.base import BaseBrain, BrainRuntime, BrainSpec
+from services.brains.base import (
+    BaseBrain,
+    BrainRuntime,
+    BrainSpec,
+    SessionVariableUpdate,
+)
 from services.knowledge import search as search_knowledge
 from services.runtime_variables import DynamicVariableStore
 from services.tool_executor import ToolExecutionError, ToolExecutor
@@ -258,6 +263,27 @@ class WorkflowBrain(BaseBrain):
             node_id=current_node,
         )
 
+    async def on_session_update(
+        self,
+        dynamic_variables: dict[str, Any],
+    ) -> SessionVariableUpdate:
+        if self._ended:
+            raise ValueError("工作流会话已经结束")
+        changed = self._store.assign_declared_many(dynamic_variables)
+        current = self._state.current_node_id
+        if changed and current and self._engine.node_type(current) == "agent":
+            await self._refresh_agent_prompt(current)
+        if changed:
+            await self._emit_variables(
+                reason="session_update",
+                node_id=current or None,
+                changed=changed,
+            )
+        return SessionVariableUpdate(
+            changed=changed,
+            dynamic_variables=self._store.public_values(),
+        )
+
     def record_user_message(self, content: str) -> None:
         if content and not self._ended:
             self._store.record("user", content)