Merge lane base check: develop 61ea898104a5

Merge lane base check: run the full gate on `develop` at `61ea898104a54dd7fca0bd1b0b72556c840f562c` alone and report it certified or red: nothing had certified it since the last attempt. A red verdict files a fix task; it never holds the lane. Filed by the control plane (`app/merge_lane.py::_certify_idle`). How: run `python3 tools/merge_lane.py run` once. It takes this check's batch, gates that commit with the full gate in its sandbox and reports `certified` or `develop_red` itself. Never run the gate by hand: a hand-run green reports nothing, so no certificate is recorded.

develop 61ea898104 red (develop_red reported, 2× deterministic): deploy_probe.py:209 start_new_session breaks POSIX-only suite; production_qa/metric_pulls.py + agent_router/decisions.py imports unresolved in CE tree break mirror-trees + CE tooling. Memory: none applied