Cross-border payments are full of free-text and fat-fingered identifiers. This kernel validates them deterministically: IBAN by its ISO-13616 mod-97 checksum and per-country length, BIC by ISO-9362 structure, and the amount against its currency's ISO-4217 minor units (a 3-decimal USD amount is wrong; for JPY, any decimal is). Edit a field and watch it validate.
Honest scope. A deterministic, signable primitive in the kernel family. It validates the IDENTIFIERS in a payment message — it does not move money, call SWIFT, or look up account ownership (mod-97 proves the IBAN is well-formed, not that the account exists). It's the deterministic guard that pairs with an agent's LLM parse of an ISO-20022 / SWIFT MT narrative: the agent extracts, this kernel checks. IBAN lengths cover 72 of the ~85 ISO-13616 registry countries — an unlisted country is flagged unknown_country, never silently passed (fail-closed); ISO-4217 minor units cover the major + 0/3-decimal currencies (unknown codes are flagged, not assumed). Source: flowdesk-finid-kernel.js.