MODE 1 — BROADCAST. Deliver a notification to EVERY connected session's GET
listener (the notifications/*/list_changed fan-out): each distinct session
MUST be told the list changed, not just the first eligible stream. Listeners
are grouped by their session token and the single-stream deliver runs once
per distinct token, so the transport's Multiple Connections rule ("MUST NOT
broadcast the same message across multiple streams") is still honoured WITHIN
a session (only one of a session's streams receives it) while distinct
sessions each get their own copy. The session token is otherwise IGNORED:
broadcast reaches all sessions, including the unscoped/stateless one.
Eligibility per listener is the shared listenerEligible decision. Returns
the number of distinct sessions reached.
MODE 1 — BROADCAST. Deliver a notification to EVERY connected session's GET listener (the notifications/*/list_changed fan-out): each distinct session MUST be told the list changed, not just the first eligible stream. Listeners are grouped by their session token and the single-stream deliver runs once per distinct token, so the transport's Multiple Connections rule ("MUST NOT broadcast the same message across multiple streams") is still honoured WITHIN a session (only one of a session's streams receives it) while distinct sessions each get their own copy. The session token is otherwise IGNORED: broadcast reaches all sessions, including the unscoped/stateless one. Eligibility per listener is the shared listenerEligible decision. Returns the number of distinct sessions reached.