Sensors: The Other Half of the Harness

The pre-commit hook caught a migration last Tuesday that would have shipped to staging green and broken production on the next deploy. The migration dropped a foreign key constraint without naming a backfill plan, and the rule that said every constraint change needs a backfill plan had been sitting in migrations.md for four months. The rule didn’t stop the agent. The rule didn’t stop the human reviewer either. The diff was 38 files and the constraint drop was a single line. What stopped it was a four-line s