Pattern

Configuration for opening a new peer session.

Forward-compatible: new fields should be added with defaults so existing callers are unaffected.

roomKey is this host's stable room identity — the value a joiner must target to be admitted. It defaults to null, meaning this host declares no room and admits any joiner (the permissive default); set it explicitly to bind admission to a room, e.g. when several hosts share a session name but must remain distinct rooms (e.g. two host() sessions on one flat in-memory mesh). A joiner declares which room it wants via Tag.roomKey; the host admits only when the targets agree (or either side names none — see Tag.roomKey).

Keeping this nullable — rather than defaulting it to sessionName — keeps room identity an explicit, opt-in concept, orthogonal to the (already overloaded) session name.