Mission Run Overview
Mission Run: Gate-Artifact Merge Driver Unit Gate
Restore driver-level unit coverage for the #2804 gate-artifact merge invariant against the #3076 row-union model, so a filled acceptance/issue criterion is never reset to a scaffold placeholder.
Commit b04da00e1 deleted the unit gate (tests/merge/test_gate_artifact_merge_drivers_2804.py) that held the #2804 invariant at merge-driver level, and it was built for the pre-#3076 whole-file fill-score heuristic that no longer exists. The only remaining coverage is a slow subprocess integration marker plus a general row-union sibling test; neither pins the #2804-specific scaffold-clobber + evidence-survival contract. This mission restores a narrow, fast in-memory unit gate calling the pure row-union reconcilers directly. It does not touch the integration marker and does not fix the #3231 product defect (the gate admits 'pending').