ah-if2 lineage audit: nothing reconciles board reality against task_parents Lined Up

Found while fixing ah-1cx.11, which hardened the WRITE path (a lost RecordChild now holds the card and retries) but left the read side unverified.

task_parents is the only source of truth for the Blocked join, and nothing checks it against the board. Two states remain undetectable: a child card created by hand (or by an older binary) that has no lineage row, and a lineage row whose card was deleted from the board. The first makes a parent under-wait; the second makes it wait forever on a card that no longer exists.

A periodic audit — walk task_parents against a board Snapshot, report rows whose card is gone and cards whose parent link is missing — would close it. Note ah-wd4.1 established that a Snapshot must REFUSE rather than return a partial board, so the audit inherits that: it must not treat a truncated snapshot as 'these cards were deleted'.

A lineage row whose card no longer exists, and a blocked parent waiting on one, are both surfaced to the operator rather than deadlocking silently. The audit refuses to act on an incomplete board snapshot.