V23 introduced a JSONB check constraint (chk_annotation_polygon_quad) requiring polygon arrays to have exactly 4 points. V30 introduced a partial unique index preventing two concurrent RUNNING training runs. These are DB-level invariants that unit tests cannot verify — five Testcontainers tests now assert they are correctly applied by Flyway and enforced by PostgreSQL. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>