perf(nests): index room presence separately from chat for O(speakers) scans

LiveActivitiesChannel.notes is mixed-kind (chat, zaps, raids, clips, presence),
and chat dominates by volume in active rooms. The Nests feed filter scanned it
twice per room per recompute -- once for any-fresh-presence, once for fresh
on-stage presence -- doing an `is MeetingRoomPresenceEvent` cast on every chat
message just to find the speakers.

Add a presenceNotes index on LiveActivitiesChannel keyed by author pubkey
(presence is replaceable per author, so the key auto-collapses heartbeats).
Populate it from LocalCache.consume(MeetingRoomPresenceEvent). Switch
NestsFeedFilter to a single hasFreshSpeakers() pass over the index, dropping
the now-redundant isLiveByPresence() check (hasFreshSpeakers implies it).
Migrate NestsFeedLoaded's latest-presence flow to the same index.

amethyst/src/main/java/com/vitorpamplona/amethyst/model/LocalCache.kt

@@ -1556,6 +1556,10 @@ object LocalCache : ILocalCache, ICacheProvider {
      * presence event needs to be in there alongside chat. Without
      * this, presence-driven inclusion can't see follows broadcasting
      * in the room (only chat-driven inclusion would fire).
+     *
+     * Also indexed under [LiveActivitiesChannel.presenceNotes] keyed
+     * by author so the Nests feed can answer "are there speakers on
+     * stage?" without scanning the chat-dominated `notes` map.
      */
     fun consume(
         event: MeetingRoomPresenceEvent,
@@ -1573,6 +1577,7 @@ object LocalCache : ILocalCache, ICacheProvider {
         val channel = getOrCreateLiveChannel(roomAddress)
         val versionNote = getOrCreateNote(event.id)
         channel.addNote(versionNote, relay)
+        channel.addPresenceNote(versionNote)
 
         return new
     }

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/nests/NestsFeedLoaded.kt

@@ -291,9 +291,9 @@ private fun observeRoomLatestPresence(
             channel
                 .flow()
                 .notes.stateFlow
-                .mapLatest { state ->
+                .mapLatest { _ ->
                     var max: Long? = null
-                    state.channel.notes.forEach { _, note ->
+                    channel.presenceNotes.forEach { _, note ->
                         val event = note.event
                         if (event is MeetingRoomPresenceEvent) {
                             val createdAt = event.createdAt

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/nests/dal/NestsFeedFilter.kt

@@ -90,7 +90,6 @@ class NestsFeedFilter(
             val noteEvent = it.event as? MeetingSpaceEvent ?: return@filterTo false
             if (!hasMinimumNestFields(noteEvent)) return@filterTo false
             if (!isWithinPlannedWindow(noteEvent, now)) return@filterTo false
-            if (!isLiveByPresence(noteEvent, presenceCutoff)) return@filterTo false
             if (!hasFreshSpeakers(noteEvent, presenceCutoff)) return@filterTo false
 
             if (filterParams.match(noteEvent, it.relays)) return@filterTo true
@@ -151,47 +150,23 @@ class NestsFeedFilter(
             starts < now + PLANNED_MAX_FUTURE_SECONDS
     }
 
-    /**
-     * Drop OPEN/PRIVATE rooms that have no kind-10312 presence in the
-     * last [PRESENCE_FRESHNESS_WINDOW_SECONDS] AND were not created in
-     * the same window. The "created recently" grace lets brand-new
-     * rooms surface before any speaker has had time to publish their
-     * first heartbeat. Mirrors the NostrNests lobby gate — needs the
-     * lobby-wide kind-10312 REQ added in `filterNestsGlobal` to be
-     * meaningful.
-     *
-     * CLOSED and PLANNED rooms bypass this gate: CLOSED rooms may
-     * carry a recording (EGG-11), and PLANNED rooms have not started
-     * yet so no presence is expected.
-     */
-    private fun isLiveByPresence(
-        event: MeetingSpaceEvent,
-        presenceCutoff: Long,
-    ): Boolean {
-        val status = event.status()
-        if (status != StatusTag.STATUS.LIVE && status != StatusTag.STATUS.PRIVATE) return true
-        if (event.createdAt > presenceCutoff) return true
-
-        val channel = LocalCache.getLiveActivityChannelIfExists(event.address()) ?: return false
-        var fresh = false
-        channel.notes.forEach { _, note ->
-            if (fresh) return@forEach
-            val e = note.event
-            if (e is MeetingRoomPresenceEvent && e.createdAt > presenceCutoff) fresh = true
-        }
-        return fresh
-    }
-
     /**
      * Drop OPEN/PRIVATE rooms whose live speaker slate is empty. A room
-     * with no fresh kind-10312 presence carrying `onstage=1` has no one
-     * left on stage — even if the kind-30312 status still says `live`,
-     * there is nothing to listen to and the room has effectively ended.
+     * with no fresh kind-10312 presence carrying `onstage=1` published
+     * in the last [PRESENCE_FRESHNESS_WINDOW_SECONDS] has no one left
+     * on stage — even if the kind-30312 status still says `live`,
+     * there is nothing to listen to and the room has effectively
+     * ended. Mirrors (and tightens) the NostrNests lobby gate.
      *
-     * Same created-at grace as [isLiveByPresence] so brand-new rooms
-     * surface before the first speaker heartbeat arrives. CLOSED and
-     * PLANNED rooms bypass this gate for the same reasons listed on
-     * [isLiveByPresence].
+     * Brand-new rooms get a created-at grace so they surface before
+     * the first speaker heartbeat arrives. CLOSED rooms bypass this
+     * gate (they may carry a recording — EGG-11), as do PLANNED rooms
+     * (not started yet, no presence expected).
+     *
+     * Reads the room's [LiveActivitiesChannel.presenceNotes] index
+     * (keyed by author, populated by
+     * `LocalCache.consume(MeetingRoomPresenceEvent)`) so the scan is
+     * O(speakers) instead of O(all chat + zaps + presence).
      */
     private fun hasFreshSpeakers(
         event: MeetingSpaceEvent,
@@ -203,7 +178,7 @@ class NestsFeedFilter(
 
         val channel = LocalCache.getLiveActivityChannelIfExists(event.address()) ?: return false
         var hasSpeaker = false
-        channel.notes.forEach { _, note ->
+        channel.presenceNotes.forEach { _, note ->
             if (hasSpeaker) return@forEach
             val e = note.event
             if (e is MeetingRoomPresenceEvent && e.createdAt > presenceCutoff && e.onstage() == true) {

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/nip53LiveActivities/LiveActivitiesChannel.kt

@@ -26,9 +26,11 @@ import com.vitorpamplona.amethyst.commons.model.Note
 import com.vitorpamplona.amethyst.commons.model.User
 import com.vitorpamplona.amethyst.commons.util.toShortDisplay
 import com.vitorpamplona.quartz.nip01Core.core.Address
+import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.nip01Core.tags.aTag.ATag
 import com.vitorpamplona.quartz.nip19Bech32.entities.NAddress
 import com.vitorpamplona.quartz.nip53LiveActivities.streaming.LiveActivitiesEvent
+import com.vitorpamplona.quartz.utils.cache.LargeCache
 
 @Stable
 class LiveActivitiesChannel(
@@ -40,6 +42,24 @@ class LiveActivitiesChannel(
     // Important to keep this long-term reference because LocalCache uses WeakReferences.
     var infoNote: Note? = null
 
+    /**
+     * Audio-room presence index (NIP-53 kind-10312) keyed by author
+     * pubkey. Presence is replaceable (one per author), so keying on
+     * the author auto-collapses heartbeat versions instead of growing
+     * unbounded the way `notes` does. Empty for streaming channels
+     * (kind-30311) — only kind-30312 rooms publish presence.
+     *
+     * Lets feeds answer "is anyone live on stage in this room?"
+     * without scanning the chat-dominated `notes` map. See
+     * [com.vitorpamplona.amethyst.ui.screen.loggedIn.nests.dal.NestsFeedFilter].
+     */
+    val presenceNotes = LargeCache<HexKey, Note>()
+
+    fun addPresenceNote(note: Note) {
+        val author = note.author?.pubkeyHex ?: return
+        presenceNotes.put(author, note)
+    }
+
     fun address() = address
 
     override fun relays() = info?.allRelayUrls()?.toSet()?.ifEmpty { null } ?: super.relays()