A mountable Rails engine that ships OpenReceive's receive-only checkout routes into a Rails app. Engine controllers inherit from the host's ApplicationController (keeping its authentication, current_user, and forgery protection; the shared handler adds JSON-only and same-site gates), delegate to the openreceive-server Service, and obey host-supplied authorization, amount-resolution, and settlement hooks. The engine owns the OpenReceivePayment attempt model, its status state machine, settlement write-once, and reconciliation (OpenReceive.reconcile!, OpenReceive::ReconcileJob, rake openreceive:reconcile); its install generator emits only the migration, initializer, and route mount. Receive-only: it never exposes a spend path, and boot fails closed on spend-capable NWC codes.