Phase 20 now has WebSocket, EventSource, BroadcastChannel, and streaming primitives. Add integration-level smoke coverage that exercises the milestone workflows end to end rather than only isolated unit tests.
Acceptance criteria:
- Add a deterministic local WebSocket echo test covering open, text message echo, close, and close event fields.
- Add a deterministic local EventSource test covering multiple events, id tracking, retry parsing, and custom event names.
- Add a BroadcastChannel document/worker delivery test for same-origin contexts.
- Add a fetch-through-TransformStream smoke test for a large response body.
- Keep tests offline and deterministic, using local test servers/harnesses only.