Presence

Strata presence is built on beryl Presence per document topic.

Presence payloads are defined in strata_protocol and are intended to cover cursor, selection, display name, and color.

Placeholder lifecycle

1. Client joins a document topic.
2. Client sends presence_set with current user metadata.
3. Server broadcasts presence_state or presence_diff.
4. Clients render remote cursors and selections from latest presence data.