# Todo 40: Chat Message Stream Audit Boundaries

## Goal

Add audit events around ChatAgent visible message streaming so replay can show when user-visible text starts and when it ends.

## Plan

1. Emit `chat_message_stream_started` before the first `message_delta` reaches the output queue.
2. Emit `chat_message_stream_finished` after the model stream ends and before `chat_agent_response`.
3. Keep `chat_agent_response` as the complete aggregated visible ChatAgent text for that call.
4. Add readable Audit Replay summaries for the new events.

## Verification

- `uv run pytest tests/test_debug_runtime.py::test_runtime_audits_chat_message_stream_boundaries_in_output_order -q`
- `uv run pytest tests/test_debug_runtime.py::test_runtime_emits_audit_events_and_backend_logs -q`
- `uv run pytest tests/test_websocket_api.py::test_static_app_handles_audit_messages -q`
- `uv run pytest`
- `node --check src/agent_lab/presentation/static/app.js`
- `git diff --check`