Walks the tenant's hash chain on one audit plane and reports what it finds.
Every row is re-checked from its own persisted columns: the envelope HMAC still
reproduces, the sequence has no gap and no repeat, each row links to its
predecessor, and the keyed row hash recomputes.

The verdict is derived on every call. No result is cached — a stale
"verified OK" is precisely the assurance this endpoint exists to replace.

The walk is paged and budgeted. A run that stops at its budget reports
complete: false with the window it did cover; call again to continue from
where it stopped. Pass fromGenesis=true to re-prove the chain from its origin
regardless of any recorded checkpoint.

A resumed run re-reads the row its predecessor stopped at before it skips
anything, so a row altered after it was verified is still caught.