zat 0.4.3 makes collectBlocks emit the block for an empty MST node instead of mistaking it for an unloaded stub and skipping it. Two repos on this PDS carried an empty subtree node minted by a pre-0.3.19 writer whose block was never stored; the first tree walk to reach it returned PartialTree, taking every createRecord to 500 and getRepo to 404 regardless of collection. The fix is self-healing — a write that does not descend into the stranded branch still commits, and the collect pass restores the missing block. Also handles zat.cbor.Value.float, new in 0.4.2, in the CBOR -> ATProto JSON writer. Adds docs/incident-2026-08-18-empty-mst-node.md with the full investigation. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>