MODE 2 — PUSH TO SESSION. Deliver a notification on exactly ONE connected
stream of the ONE session named by sessionToken, used by
notifications/resources/updated to a subscriber. The chosen stream still
applies its own per-stream SubscriptionFilter (resource-updated URI/type
filtering) and per-session gate via the shared listenerEligible decision,
so a session's update reaches only a stream that opted into this method
(and, for resources/updated, this uri). An empty sessionToken is the
unscoped path: every listener is a candidate (the draft self-contained
subscriptions/listen stream and the stateless/no-session case), matching
the prior single-stream filtered delivery. Returns 1 if delivered, else 0.
MODE 2 — PUSH TO SESSION. Deliver a notification on exactly ONE connected stream of the ONE session named by sessionToken, used by notifications/resources/updated to a subscriber. The chosen stream still applies its own per-stream SubscriptionFilter (resource-updated URI/type filtering) and per-session gate via the shared listenerEligible decision, so a session's update reaches only a stream that opted into this method (and, for resources/updated, this uri). An empty sessionToken is the unscoped path: every listener is a candidate (the draft self-contained subscriptions/listen stream and the stateless/no-session case), matching the prior single-stream filtered delivery. Returns 1 if delivered, else 0.