Message Broker

Ownership and transitions

A retained FIFO log is shared content; each consumer group owns its cursor, in-flight flag, attempt, and dead letters. Repeated polling returns the same attempt, while a retry rejection clears ownership and increments only on redelivery. An acknowledgment advances only a matching current in-flight ID. At the attempt limit append once to that group DLQ and continue. Retention grows with messages and group failures; no timeout is implicit.

JavaScript boundaries

Use native classes with per-instance state and plain object/array snapshots. Object assignment shares a reference; copy retained inputs and every outward mutable container, including nested arrays. null means absence. Map handles arbitrary string keys safely, including "__proto__"; do not confuse a missing key with zero or an empty string. Domain validation uses RangeError. Numeric inputs must satisfy Number.isSafeInteger, so booleans, fractions, infinities, and NaN are invalid where an integer is required. All documented aggregate results and timestamp-plus-duration sums fit the safe-integer range. Strings use exact case-sensitive equality; lexical order compares JavaScript UTF-16 code units. Calls are serialized and synchronous.

const internal = ["initial"];
const snapshot = [...internal];
snapshot.length = 0;
console.assert(internal.length === 1);

A detached snapshot protects ownership; the service still has to validate and commit a coherent transition.