Adding a schema change

Edit the model in service/src/db/models.py, then generate a revision from the diff and review it before committing — autogenerate is a starting point, not the final migration:

cd service
alembic revision --autogenerate -m "add foo column to pipeline_runs"

Check the generated file in migrations/versions/ for: correct batch_alter_table usage on anything SQLite can’t ALTER directly, a sane downgrade(), and that a backfill (if the change needs one) is written explicitly — autogenerate only emits schema-shape DDL, never data migrations. test_database_migrations.py’s drift-guard test fails CI if a model change ships without a matching revision.

For how migrations run at deploy time (auto-migrate on boot vs. a DBA-run step), see Deployment.