Verify a window of the hash-chained decision ledger (resumable via afterSeq)

Responses

• 200
  Window verified clean; nextAfterSeq is the resume cursor (null at the tip). Every response also carries tipSeq/tipHash/totalCount for third-party checkpointing, contentMismatches (#9850 -- the COUNT of rows whose preimage no longer matches the digest the chain committed to; a content mismatch no longer aborts the scan, because one unreconcilable row used to hide every row after it, so a structural break further along was unreachable. The verdict is unchanged: any mismatch is still ok:false and the first is still reported as `break`), and prunedRecords — the count of rows whose record preimage was legitimately pruned by the published retention window (chain checks still hold for them; only the content re-check is impossible, and the committed digest stays published).
• 409
  First break found: sequence_gap | predecessor_mismatch | row_hash_mismatch | missing_record | content_mismatch | short_tail (a record newer than the verified tip has no chain entry — the truncated-tail signature) | unchained_record (an INTERIOR record has no chain entry — the failed-append signature). Records younger than the 5-minute append grace window are not reported: the record insert and its chain append are two writes moments apart, and a verify landing between them is not evidence of tampering.