Seeking champion: signed delivery receipts + dispute window for x402 on Canton (RFP 13)

Looking for a Tech & Ops champion before filing an RFP 13 (Payments and DeFi) PR. If another channel is preferred, say so and I will close this.

Scope: x402 on Canton (#78) settles the payment, but the payee, auditor or adjudicator gets no signed record of what was delivered and no window to dispute it before funds are final. We'd add that on top of the FTP facilitator and the ChainSafe SDK, not as a rewrite:

• Daml ReceiptRecord / DeliveryVerdict with provisional->final status and an auditor signatory
• TS library, spec and test vectors for offline verification
• adapters for the FTP facilitator and ChainSafe SDK

Prototype (Apache-2.0, Daml tests run on a local Canton 3.6 sandbox): https://github.com/predgeAI/x402-receipts

Ask: 600k CC, 12 weeks to MainNet, ~half paid only on external adoption.

@Jatinp26 @srikanth-bitdynamics @Ian-avro would any of you champion this, or review the scope first?