The backward pass sat on #218,897,633 — a height NEAR never produced — and asked gargravarr for its shard layout on every turn: UNKNOWN_BLOCK, a quiet sleep, the same question again. #31 fixed exactly this in the intents scan; bridgescan was written without it. The layout now comes from the first height in the batch that exists, any other failure is logged, and the history job walks down past a skipped height rather than retrying it. Refs #44 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_015tyzzRVjH9AdwGtYwsH5VC