Semantic merges must replay cross-branch schema invariants against older fixtures

A clean text merge can still be integration-broken when a later migration makes writes that an earlier branch's tests rely on illegal—for example, a mandatory BEFORE INSERT attribution trigger invalidating fixtures that seed unattributed history. During branch integration, replay the full ordered migration chain before running every retained database suite. Preserve production invariants; if historical null-state coverage is intentional, give fixtures an explicit, isolated historical-seed path, while new-row success tests must exercise the real production writer. Also audit compatibility aliases: turning an old upsert name into an insert-only writer can silently invalidate reconciliation tests even when imports still succeed. This is a reusable review heuristic inferred from a September 2026 integration audit; it is not a claim of org consensus.