feat: add stateful responses API

backend/services/brains/prompt_brain.py

@@ -83,6 +83,7 @@ class PromptBrain(BaseBrain):
         self._startup_failed = False
         self._greeting_pending = False
         self._entry_dispatched = False
+        self._restored_text_state: dict[str, Any] | None = None
 
     async def greeting(self, cfg: AssistantConfig) -> str:
         # The built-in opening Message owns the greeting so speech and the
@@ -127,6 +128,12 @@ class PromptBrain(BaseBrain):
         self._startup_failed = False
         self._greeting_pending = False
         self._entry_dispatched = False
+        if self._restored_text_state is not None:
+            state = self._restored_text_state
+            self._preflight_finished = bool(state.get("preflight_finished"))
+            self._opening_finished = bool(state.get("opening_finished"))
+            self._opening_started = self._opening_finished
+            self._entry_dispatched = bool(state.get("entry_dispatched"))
         schemas: list[FunctionSchema] = []
         registered_names: set[str] = set()
         binding_by_id = {binding.tool_id: binding for binding in cfg.tool_bindings}
@@ -171,6 +178,21 @@ class PromptBrain(BaseBrain):
             )
         runtime.set_tools(schemas)
 
+    def restore_text_state(self, snapshot: dict[str, Any]) -> None:
+        """Restore Prompt startup progress for a later Responses API turn."""
+        if snapshot.get("type") != "prompt":
+            raise ValueError("Responses runtime state does not belong to a prompt")
+        self._restored_text_state = dict(snapshot)
+
+    def text_state_snapshot(self) -> dict[str, Any]:
+        """Prevent completed startup actions from running again next turn."""
+        return {
+            "type": "prompt",
+            "preflight_finished": self._preflight_finished,
+            "opening_finished": self._opening_finished,
+            "entry_dispatched": self._entry_dispatched,
+        }
+
     async def setup_realtime(
         self,
         cfg: AssistantConfig,