Cost Aware and Compliance Safe AID Debit Routing for Retail Payment Gateways

Regulated debit routing sits at the intersection of EMV standards, Durbin routing rights, and acquirer engineering practice, yet in many gateways AID selection is buried in opaque configuration and ad hoc code. This makes it difficult to reason about merchant cost, acceptance rates, or even basic compliance with scheme and regulatory rules. This paper presents a cost aware and compliance safe AID debit routing engine for retail payment gateways. We first define a standards accurate policy model that encodes EMV debit routing constraints, Durbin style requirements for regulated domestic cards, and merchant routing preferences as machine readable rules. On top of this model, we design a constrained optimization algorithm that selects a primary network and fallback order to minimize expected routing cost subject to acceptance and tail latency constraints while respecting all policy guardrails. To support reproducibility, we release a synthetic AID routing dataset and a trace driven simulator with fault injection that enable controlled experiments over issuer mix, fee schedules, outages, and misconfigurations. Using this framework, we show that the proposed engine can reduce expected routing fees relative to a brand first baseline, keep p99 routing latency within the same budget, and eliminate simulated Durbin style violations even under adverse network and configuration scenarios.