feat: add session updates and message dialogs

backend/services/brains/prompt_brain.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+from typing import Any
 from uuid import uuid4
 
 from models import AssistantConfig
@@ -15,10 +16,13 @@ from pipecat.services.llm_service import (
 )
 from pipecat.utils.time import time_now_iso8601
 
-from services.brains.base import BaseBrain, BrainRuntime, BrainSpec
-from services.runtime_variables import (
-    DynamicVariableStore,
+from services.brains.base import (
+    BaseBrain,
+    BrainRuntime,
+    BrainSpec,
+    SessionVariableUpdate,
 )
+from services.runtime_variables import DynamicVariableStore
 from services.tool_executor import ToolExecutionError, ToolExecutor
 from services.tool_policy import policy_for_tool
 
@@ -76,6 +80,18 @@ class PromptBrain(BaseBrain):
         self._store.record("user", content)
         self._refresh_prompt()
 
+    async def on_session_update(
+        self,
+        dynamic_variables: dict[str, Any],
+    ) -> SessionVariableUpdate:
+        changed = self._store.assign_declared_many(dynamic_variables)
+        if changed:
+            self._refresh_prompt()
+        return SessionVariableUpdate(
+            changed=changed,
+            dynamic_variables=self._store.public_values(),
+        )
+
     async def on_assistant_text_start(self, _turn_id: str) -> None:
         if self._runtime is not None:
             self._runtime.call_end.begin_response()