The five-layer stack behind “invisible” stablecoin funding in consumer apps

There's a recurring architectural question in consumer fintech right now: how do you use stablecoin settlement rails without making the user aware of them?

The stack that's emerging tends to have five components working together:

1. Fiat on-ramp with local payment method coverage (UPI, SEPA, PIX, ACH, etc.)
2. Custody or wallet architecture that the product layer abstracts
3. KYC and transaction monitoring that doesn't re-screen users already verified by the partner
4. Rail orchestration that selects between fiat and chain-based routing based on corridor and cost
5. Settlement output in whatever the back office actually wants: fiat, stablecoin, or both

The interesting engineering constraint is that most neobanks want to own layers 1 and 5 (the user experience and the back-office output) and have someone else carry the compliance and chain routing complexity in the middle.

That creates a real integration architecture question. Do you build a thin wrapper over multiple point solutions? Do you find infrastructure that handles the full middle stack? How do you make sure KYC state from the partner's onboarding flow passes through correctly without re-KYCing users at the on-ramp layer?

We've worked through this with a few neobank integrations and the KYC passthrough piece tends to be the one that creates the most friction if the architecture isn't settled early.

What are people seeing as the cleanest solution for chain selection and corridor routing in this stack?