Scenario 1: checkout-api — Connection Pool Exhaustion

A v2.4.1 deploy to checkout-api introduced an N+1 query pattern that exhausted the database connection pool 22 minutes later, spiking checkout errors from under 1% to 40%.

Steps to test

1. Open INC0000001.
2. Steps 4–7: db_connection_wait_ms ramps from 2ms to 890ms; a trace on POST /checkout shows "connection pool exhausted, waited 890ms".
3. Step 8: the v2.4.1 deploy, 22 minutes earlier, is the single change candidate.
4. Steps 10–11: top hypothesis at 0.88 confidence (change-sourced).
5. Step 12: already approved.
6. Steps 13–14: rollback and pool increase executed live, verification RESOLVED.