nostrnests publishes kind-30312 without a self-`p`-tag for the room
author — they're the implicit host. The lobby card already handles
this (NestJoinCard) but the in-room code did not: the author fell
into the pure-audience branch with role=null AND was missing from
the audio subscription set, so the host appeared as a regular
listener and no sound played.
buildParticipantGrid now takes hostPubkey and synthesizes a virtual
`["p", host, "", "host"]` when absent, so the existing presence-aware
onstage/audience rules apply uniformly — including "host leaves
stage" (onstage=0 → drops to audience, role stays HOST).
NestActivityContent owns the grid now and derives onStageKeys from
it, so the StageGrid render and the MoQ subscription set stay in
lockstep when anyone (host or speaker) steps off stage.
Vitor Pamplona
20a2270434