Add support for prefix state code

engine/config.py

@@ -107,11 +107,20 @@ class TurnConfig:
     )
 
 
+@dataclass(frozen=True)
+class ResponseStateConfig:
+    enabled: bool = False
+    tag: str = "state"
+    event_type: str = "response.state"
+    max_prefix_chars: int = 256
+
+
 @dataclass(frozen=True)
 class AgentConfig:
     system_prompt: str = "You are a helpful, friendly voice assistant."
     greeting: str | None = None
     greeting_mode: str = "generated"
+    response_state: ResponseStateConfig = field(default_factory=ResponseStateConfig)
 
 
 @dataclass(frozen=True)
@@ -220,6 +229,13 @@ def config_from_dict(data: dict) -> EngineConfig:
         agent["greeting"] = None
     if agent.get("greeting_mode") not in (None, "generated", "fixed", "off"):
         raise ValueError("agent.greeting_mode must be one of: generated, fixed, off")
+    response_state = ResponseStateConfig(**_dict(agent.pop("response_state")))
+    if response_state.max_prefix_chars < 1:
+        raise ValueError("agent.response_state.max_prefix_chars must be greater than 0")
+    if not response_state.tag:
+        raise ValueError("agent.response_state.tag must not be empty")
+    if not response_state.event_type:
+        raise ValueError("agent.response_state.event_type must not be empty")
 
     stt = _dict(services.get("stt") or services.get("asr"))
     if stt.get("language") == "":
@@ -260,7 +276,7 @@ def config_from_dict(data: dict) -> EngineConfig:
                 )
             ),
         ),
-        agent=AgentConfig(**agent),
+        agent=AgentConfig(**agent, response_state=response_state),
         services=ServicesConfig(
             llm=LLMConfig(**llm),
             stt=STTConfig(**stt),