Hard latency budget for just-in-time authorization routing

Context

Real-time card routing runs inside the card-network authorization window. A routing decision that arrives late is useless — the transaction has already authorized on the default card.

Decision

The JIT routing path operates under a strict deadline (default 3000ms) enforced end-to-end. If the optimizer cannot return within budget, the transaction proceeds on the default card rather than blocking the authorization.

Consequences

• Routing never degrades the checkout experience; worst case is an un-optimized (not failed) purchase.
• The optimizer is built to be cheap and synchronous on the hot path; expensive analysis is deferred off the authorization window.
• Latency is observable per-transaction so regressions surface quickly.