a2ff193050
- Expand migration comment to name the primary failure mode (missing column OperationalError from #20842) ahead of the secondary SQLite schema-reparse concern; also document the stale-cols-snapshot invariant - Add clarifying comments on from_row() legacy fallback branches noting they are belt-and-suspenders dead code post-migration - Add task_events comment in existing test explaining why the table is required by the migrator - Add test_legacy_migration_no_legacy_columns_at_all: Scenario A — explicitly asserts the exact #20842 crash no longer occurs and that consecutive_failures defaults to 0 on a DB that never had spawn_failures - Add test_legacy_migration_both_columns_already_present: Scenario D — asserts the migration is a no-op when both columns already exist, preserving the existing counter value