zat.dev held three stranded empty nodes, not one — the original sweep deduped by CID and every empty node shares a CID. All three cleared by ordinary forward create-then-delete commits; its served root now matches a canonical fresh rebuild. Adds the atproto spec citations that establish an empty subtree pointer as invalid, and records the applyWrites batch-ordering divergence from the reference PDS and tranquil. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>