Recomputes every record hash from a canonical JSON representation of id, sequence, timestamp, previous_hash and payload, then checks that each record points to the hash of the record before it. If a root_hash is supplied, the same computed record hashes are folded into a deterministic binary Merkle tree with the last leaf duplicated on odd levels.

Providers each build their signing string differently — some sign only the body, others prepend a timestamp, an id, or a version marker in a fixed order — and getting that order wrong produces a mismatch that looks exactly like an attack. This checks the signature the way the named provider actually specifies, with constant-time comparison, and returns the string that was signed so a mismatch can be debugged instead of guessed at.