OptionalclaimOptionalidempotencyCaller dedupe token, unique per customer. A repeat returns the escrow the
first call made, with replayed: true, and builds nothing.
OptionalmessageOptionalmetadataWho funds the escrow: one of the sender identity's own ledger accounts.
Human-decimal amount (e.g. 1.31), per the financial-services BigNumber convention. The row persists this decimal value; the mintfx builders scale it to raw base units for the on-chain amount.