Tests that call patch.dict(os.environ, clear=True) dropped
GITEA_MCP_SESSION_STATE_DIR and re-adopted the operator host cache
under ~/.cache/gitea-tools/session-state. A residual terminal
request_changes mutation then tripped the #332 hard-stop before
test_unknown_profile_blocks could assert the empty-profile gate.
- Pin mcp_session_state.default_state_dir / DEFAULT_STATE_DIR to a
per-test temp dir in conftest (still honors an explicit env override)
- Clear the decision lock at the start of each TestMergePR test
- Add regression coverage for env-clear isolation
Closes#590
