# schema_mismatch: application errors after a schema or data change (layer 3)

Symptoms: api or legacy-api 5xx with SQL errors in the logs (column does not exist, relation missing, constraint violation) while the database is reachable and replication is fine.

Decision for the human: identify the change (ask who ran it, check recent DDL), then either roll the application forward to a matching version through Git or repair the schema/data with SQL (db.data_fix, irreversible). Restarting pods does not help. The agent must escalate.