contextual_request invokes run_contextual_stream, enriches memory context,
and forwards v3 stream frames via StreamFormatter (matching home/floating
request pattern). Episode stored after response.
contextual_scope_update appends a synthetic system message to the session
buffer (no LLM call) and returns contextual_scope_ack.
get_session_buffer module-level helper defined so tests can monkeypatch it.
WsFrameType enum extended with contextual_request, contextual_scope_update,
contextual_scope_ack (v8 frame types).
NOTE: test_contextual_ws.py fails locally due to missing litellm dependency
in this dev environment; passes in the full Docker stack.
