Hash new audit entries from a TLV buffer built with one-byte field tags,
big-endian u64 byte lengths, and raw values. Absent optional fields are
omitted; present empty values retain their tag and zero length. This
prevents bytes from moving between fields without restricting object IDs
or inferring boundaries from field contents.
Store an explicit `hash_version`. Migration 0048 labels existing rows as
version 1, and new writers use version 2. Historical hashes are
unchanged and mixed-version chains verify. The legacy encoding retains
its original ambiguity; TLV protects new entries. Apply the migration
before deploying the updated writers and verifiers.
Tests cover both boundary collisions, absent versus empty fields, stable
digests, unknown versions, mixed-version chains, and stored-row
tampering. All 16 audit and 128 database unit tests passed. The six
PostgreSQL audit tests passed against both migrated and fresh schemas,
and a populated-row migration check preserved the historical hash. Full
`just ci` passed.
Related audit fixes: #4216 and #4249; issue #4173.
Signed-off-by: Jordan Mecom <jm@squareup.com>
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