test(tui): improve coverage for tui_gateway/ws.py (fixes #36617)

[Morad37]

Brings tui_gateway/ws.py coverage from 0% to 86% (150 stmts, 21 missed).

Covers: WSTransport init/write/write_async/_safe_send/close,
_ws_peer_label, _disable_nagle, and key paths in handle_ws (accept,
parse error, dispatch, ready send failure, dispatch crash).

Closes #36617

[teknium1]

Thanks for adding focused WebSocket coverage. The coverage goal is still useful, but this test file needs adaptation before it can be salvaged onto current main.

Problems

• tests/tui_gateway/test_ws.py:26 defines FakeWebSocket without close(), while current tui_gateway/ws.py:452 unconditionally awaits ws.close() in handle_ws() cleanup. The handle_ws cases will therefore fail during teardown rather than complete their assertions.
• Current main substantially changed this path after the PR base: token batching is in tui_gateway/ws.py:125-221, MCP startup is at :312-317, and disconnect teardown is at :425-450. The tests also need to isolate the new MCP-startup call and cover these current contracts.

Suggested changes

• Add an awaited close mock to the fake, patch MCP startup in handle_ws tests, and port the reusable cases to the current transport semantics.
• Add coverage for batching/order and disconnect session teardown alongside the existing parse and dispatch failures.

Automated hermes-sweeper review.

[teknium1]

handle_ws() now always awaits ws.close() in its finally block (tui_gateway/ws.py:452), but this fake does not provide close. Add an async close mock/method so the handle_ws tests can reach their assertions without failing during cleanup.