When fetchSubGroupsByPath returns only nav-crumb stubs (e.g. a "Portal"-only page for a Hyundai BODY node), the post-filter set is empty and drizzle .values([]) threw → HTTP 500. Compute `unique` unconditionally and only insert when non-empty; otherwise fall through to the leaf/parts path for a clean empty node. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>