Link is the protocol-abstraction runtime of Hellgate's Composable Payment Architecture and the PSP and provider connectivity layer of the platform. It sits between an API and whatever fulfils it: you define a versioned API contract, a protocol, and bind it to one or more real providers through declarative backends. Callers invoke the protocol. Link validates the request, maps it onto the configured backend, dispatches the call, maps the response back and logs the exchange. This cleanly separates the API a consumer codes against from the system that actually serves it. You change what is behind the API without changing the API. Key capabilities: 1. Protocol abstraction: define a versioned, schema-validated API contract once and reuse it across providers. 2. Declarative backends: bind a protocol to any provider through mapping rules, not per-vendor code. 3. Provider switching: re-point the same contract to a different backend, or run several in parallel, without the caller noticing. 4. Operational surface by default: generated OpenAPI, message-level encryption, credential and key rotation, execution audit log. 5. Integration as configuration: migrations become your config instead of your customer's project. 6. Part of the Composable Payment Architecture: works alongside Hellgate Commerce, Guardian and Specter.