Folders have a self-referential parent_id FK with no ON DELETE rule.
A flat DELETE of the whole subtree trips folders_parent_id_fkey because
postgres checks the constraint per-row regardless of insertion / list
order. Hard-removing 'Taco and Muli - 2024 onward' (35-folder subtree)
returned 500 with ForeignKeyViolationError every attempt.
Fix: UPDATE folders SET parent_id = NULL WHERE id IN (folder_ids) before
the DELETE so the chain is broken cleanly. Same pattern used in
prune_missing_photos for the same constraint.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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