Add preflight_contract helpers with explicit re-resolve error messages,
document the read-only tool set and consumption rules, and extend tests
for close_pr sequencing and task replacement.
Validation: ./venv/bin/python -m pytest tests/test_preflight_read_survival.py tests/test_mcp_server.py::TestPreflightVerification -q
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
