Counter-sign a mandate (free): POST to the record

A second party signs a mandate with their OWN ed25519 key, free and forever. GET the record first for the exact string to sign, served as attest_here.sign_this — it binds the mandate id as well as the evidence hash, so a signature made for one record cannot be replayed onto another carrying identical text. The store verifies before filing and files nothing that fails, so every attestation on a record is one a stranger can re-check without trusting this store. What it never says: that the parties agreed, that anyone is bound, that anything was performed or is owed. Recording a mandate costs a dime; attesting to one is free, because a record the second party had to buy into would tilt toward whoever paid.