Finish the Copilot review cleanup for lazy prompt submission:
- prompt.submit now claims session.running before returning success, preserving
the existing RPC-level session busy error so the frontend can queue.
- agent-init timeout/failure now emits a normal error event instead of writing a
second JSON-RPC response for an already-settled request id.
Tests:
- python -m py_compile tui_gateway/server.py tui_gateway/entry.py
- cd ui-tui && npm run type-check && npm run build
- scripts/run_tests.sh tests/tui_gateway/test_protocol.py::test_sess_found tests/tools/test_code_execution_modes.py tests/tools/test_code_execution.py
- cd ui-tui && npm test -- --run src/__tests__/useSessionLifecycle.test.ts src/__tests__/useConfigSync.test.ts
d341af22c0