Bufdir Column Schema Config Repository

This is a medium-complexity backend data component stored in Supabase. Development effort is primarily in the versioning mechanism — `listSchemaVersions` and `revertToVersion` add meaningful complexity beyond basic CRUD and should be scoped carefully. A key dependency question is who will have access to update schema configurations in production: if this is an admin-only operation through the back office, ensure the appropriate role-based access controls are in place before go-live. Testing must cover default schema fallback (when no org-specific config exists), version rollback correctness, and Supabase RLS policies to prevent one organisation from reading another's schema.

The main project risk is schema drift: if Bufdir updates their template and the config is not updated promptly, exports will fail. Plan for an admin notification or monitoring alert to flag schema version mismatches.

This backend data component provides persistent storage for per-organisation Bufdir column schema configurations in Supabase. The `getSchema` method should implement a fallback chain: org-specific schema → default schema, so new organisations inherit a working baseline without manual setup. `saveSchema` should auto-increment the version number and timestamp the record rather than overwriting in-place, enabling `listSchemaVersions` to return the full history and `revertToVersion` to restore a prior state by copying the versioned record as the new current. The schema itself (BufdirColumnSchema) should be stored as a JSONB column in Supabase for flexibility as Bufdir's template evolves.

Apply row-level security so each organisation's config is isolated. Consider caching the default schema in-process since it is read on every export and changes infrequently — invalidate on `saveSchema` calls against the default org. The bufdir_column_schema data model drives the table definition.