Reserved-name discipline.

When an entry is appended, the stream stores the record's canonical id under a field named id, alongside the payload fields. A reader recovers the id from that field and treats the rest as the payload. So a payload must not also carry a field named id: the reader could not tell the stored record id from the payload value, and one would shadow the other. Name the domain's own identifier something specific — room, game, player — and leave id to the stream.

A stream's history can be archived, and a small cache records how far the archive has advanced — under a key formed by adding a reserved suffix to the stream's key. So a stream name must not be chosen such that its key collides with that watermark key. And every key in the system lives under a reserved namespace prefix, so a custom stream lives inside that namespace rather than beside it — the name is the part after the prefix, not a free-standing key. Two mechanical rules: do not reuse the reserved suffix as part of a stream name, and let the namespace own the prefix.

The reserved set is short because the contract is narrow: one field name for the stored id, one suffix for the archive seam, one prefix for the namespace. None of them constrains the shape of a custom event — the payload can hold any fields under any other names, and a stream can be named for any event type. The discipline is a handful of names to avoid, checked once when a new event type or payload is designed, not a schema to satisfy on every append.

EchoMQ's Stream Tier makes the three reserves concrete. The record id is stored under the field id: EchoMQ.Stream.append/4 issues XADD <key> <xadd_id> id <branded> <fields…>, and on read, EchoMQ.Stream.read/6 recovers the branded id from the id field and deletes id from the payload map before returning {branded, fields_map}. A custom event that named a payload field id would have it consumed as the record id, so the field name id is reserved.

The archive seam is the second reserve. EchoMQ.Stream.put_archived/4 caches the watermark under emq:{q}:stream:<name>:archived via EchoMQ.Keyspace.queue_key/2 — the :archived sub on the stream's key. A stream name must not collide with that suffix. The third reserve is the protocol's namespace: every key is built by EchoMQ.Keyspace, braced as emq:{q}:, so a custom stream's name is the <name> in emq:{q}:stream:<name>, owned by the keyspace builder rather than a bare key. Keep custom event names and payload field names clear of id, the :archived suffix, and the emq:{q}: prefix, and the rest is the domain's to name.

In codemojex (echo/apps/codemojex), the queue is cm and the consumer surfaces — Codemojex.Guesses, Codemojex.Board, Codemojex.Scoring, Codemojex.Rooms — name their entities room, game, player rather than id, so a domain event appended to a codemojex stream leaves the id field to the record id and keeps its payload unambiguous.