Enhance WebSocket session management by requiring assistant_id as a query parameter for connection. Update API reference documentation to reflect changes in message flow and metadata validation rules, including the introduction of whitelists for allowed metadata fields and restrictions on sensitive keys. Refactor client examples to align with the new session initiation process.

engine/models/ws_v1.py

@@ -18,12 +18,6 @@ class _StrictModel(BaseModel):
     model_config = ConfigDict(extra="forbid")
 
 
-# Client -> Server messages
-class HelloMessage(_StrictModel):
-    type: Literal["hello"]
-    version: Literal["v1"] = Field(..., description="Protocol version, fixed to v1")
-
-
 class SessionStartAudio(_StrictModel):
     encoding: Literal["pcm_s16le"] = "pcm_s16le"
     sample_rate_hz: Literal[16000] = 16000
@@ -69,7 +63,6 @@ class ToolCallResultsMessage(_StrictModel):
 
 
 CLIENT_MESSAGE_TYPES = {
-    "hello": HelloMessage,
     "session.start": SessionStartMessage,
     "session.stop": SessionStopMessage,
     "input.text": InputTextMessage,