The operational constraint changes the answer: during a delivery incident, I need to reconstruct what the notification service believed at the time, not merely flip a switch. For a small e-commerce system, I would start with an in-memory object or database-backed flag store, expose explicit toggle and read operations, and keep the provider replaceable. A simple Express.js service is enough for the first version.

Short answer: use a flag state keyed by name, make toggle writes explicit, read the value from the same source used by the notification worker, and attach the flag key and value to structured logs. That gives responders a path from a failed delivery to the decision that enabled or disabled the behavior.…