Audit roadmap T1 (alog.md §11.4): one chain per UTC calendar month of
OccurredAtUtc. Each chained row carries ChainSeq (gap-free within its month)
and RowHash = SHA-256(prev.RowHash || canonical(row)); the v1 canonical form
(AuditChainHasher) is pinned by a known-answer vector computed independently.
- Migration AddAuditLogHashChain: nullable ChainSeq/RowHash on dbo.AuditLog
(metadata-only add), AuditLogChainHead (per-month chain end + partition-purge
checkpoint anchor), AuditLogChainTombstone, two partition-aligned filtered
indexes, scadabridge_audit_chainer role with a column-level UPDATE grant.
Production script docs/plans/sql/AddAuditLogHashChain.sql.
- AuditLogHashChain chains unchained rows oldest month first under an
exclusive sp_getapplock (zero timeout, so a dual-active central pair still
yields one chain), with an optimistic head check and a ChainSeq IS NULL
row-count check that roll a pass back instead of leaving a gap. The ingest
path is untouched.
- Purges keep the chain verifiable: the partition switch records the month's
checkpoint anchor and drops its tombstones; the per-channel DELETE writes a
tombstone per chained row in the same transaction (OUTPUT INTO). Both, and
the SourceNode backfill, hold the chain lock; the backfill skips chained
rows. The switch staging table gains the two new columns.
- AuditChainVerifier reports the first break (partition, ChainSeq, EventId,
kind) for edited, deleted, reordered rows and tail truncation.
- AuditLogHashChainService (central, default OFF via AuditLog:HashChain).
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
Joseph Doherty
fd4be80913