fix nests room author shown in audience with no audio

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.

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/nests/room/activity/NestActivityContent.kt

@@ -47,6 +47,7 @@ import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.commons.model.AddressableNote
 import com.vitorpamplona.amethyst.commons.viewmodels.ConnectionUiState
 import com.vitorpamplona.amethyst.commons.viewmodels.NestViewModel
+import com.vitorpamplona.amethyst.commons.viewmodels.buildParticipantGrid
 import com.vitorpamplona.amethyst.service.relayClient.reqCommand.event.observeNoteEvent
 import com.vitorpamplona.amethyst.ui.call.KeepScreenOn
 import com.vitorpamplona.amethyst.ui.note.LoadAddressableNote
@@ -66,7 +67,6 @@ import com.vitorpamplona.amethyst.ui.stringRes
 import com.vitorpamplona.nestsclient.NestsRoomConfig
 import com.vitorpamplona.quartz.nip01Core.core.Address
 import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.MeetingSpaceEvent
-import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ROLE
 import kotlinx.coroutines.flow.SharedFlow
 
 /**
@@ -233,18 +233,28 @@ private fun NestActivityBody(
     val localPubkey = account.signer.pubKey
     val roomATag = roomNote.idHex
 
-    // Static room layout: hosts + speakers from the kind-30312 `p`-tags.
+    val ui by viewModel.uiState.collectAsState()
-    // The grid renderer derives audience from the kind-10312 presence
+    val presences by viewModel.presences.collectAsState()
-    // aggregator (see ParticipantsGrid / buildParticipantGrid); this
+
-    // composable only needs the on-stage subset for the talk-row gate
+    // Single source of truth for "who is on the stage". Built from the
-    // and the PIP renderer.
+    // kind-30312 `p`-tags + the kind-10312 presence aggregator, with
-    val onStage =
+    // the event author synthesised as the implicit HOST when they're
-        remember(event) {
+    // not in their own `p`-tags (per EGG-07; nostrnests' default).
-            event.participants().filter {
+    // This drives BOTH the StageGrid render AND the audio subscription
-                it.role.equals(ROLE.HOST.code, true) || it.role.equals(ROLE.SPEAKER.code, true)
+    // set, so the two stay in lockstep when a speaker (or the host)
-            }
+    // emits `onstage=0` to step off the stage.
+    val participantGrid =
+        remember(event, presences) {
+            buildParticipantGrid(
+                participants = event.participants(),
+                presences = presences,
+                hostPubkey = event.pubKey,
+            )
+        }
+    val onStageKeys =
+        remember(participantGrid) {
+            participantGrid.onStage.map { it.pubkey }.toSet()
         }
-    val onStageKeys = remember(onStage) { onStage.map { it.pubKey }.toSet() }
 
     AutoConnectAndTrackSpeakers(viewModel, onStageKeys)
 
@@ -264,8 +274,6 @@ private fun NestActivityBody(
     // listener + speaker when the activity finishes.
     LeaveOnRoomClosed(event, onLeave)
 
-    val ui by viewModel.uiState.collectAsState()
-
     // Hold a screen-on lock while the user is actively in the room so the
     // device doesn't lock and interrupt the audio session UI.
     if (ui.connection is ConnectionUiState.Connected) {
@@ -310,7 +318,7 @@ private fun NestActivityBody(
     if (isInPipMode) {
         NestPipScreen(
             title = event.room(),
-            onStage = onStage,
+            onStage = participantGrid.onStage,
             ui = ui,
             viewModel = viewModel,
             handRaised = handRaised,
@@ -320,7 +328,7 @@ private fun NestActivityBody(
         NestFullScreen(
             event = event,
             roomNote = roomNote,
-            onStage = onStage,
+            participantGrid = participantGrid,
             viewModel = viewModel,
             ui = ui,
             accountViewModel = accountViewModel,

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

@@ -63,7 +63,7 @@ import com.vitorpamplona.amethyst.commons.icons.symbols.Icon
 import com.vitorpamplona.amethyst.commons.icons.symbols.MaterialSymbols
 import com.vitorpamplona.amethyst.commons.viewmodels.NestUiState
 import com.vitorpamplona.amethyst.commons.viewmodels.NestViewModel
-import com.vitorpamplona.amethyst.commons.viewmodels.buildParticipantGrid
+import com.vitorpamplona.amethyst.commons.viewmodels.ParticipantGrid
 import com.vitorpamplona.amethyst.ui.navigation.topbars.ShorterTopAppBar
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.nests.room.chat.NestChatPanel
@@ -79,7 +79,6 @@ import com.vitorpamplona.quartz.nip01Core.tags.aTag.ATag
 import com.vitorpamplona.quartz.nip19Bech32.toNAddr
 import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.MeetingSpaceEvent
 import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.StatusTag
-import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ParticipantTag
 import kotlinx.coroutines.launch
 
 /**
@@ -108,7 +107,7 @@ import kotlinx.coroutines.launch
 internal fun NestFullScreen(
     event: MeetingSpaceEvent,
     roomNote: com.vitorpamplona.amethyst.model.AddressableNote,
-    onStage: List<ParticipantTag>,
+    participantGrid: ParticipantGrid,
     viewModel: NestViewModel,
     ui: NestUiState,
     accountViewModel: AccountViewModel,
@@ -143,14 +142,6 @@ internal fun NestFullScreen(
     val speakerCatalogs by viewModel.speakerCatalogs.collectAsState()
     val audioLevels by viewModel.audioLevels.collectAsState()
 
-    val onStageKeys = remember(onStage) { onStage.map { it.pubKey }.toSet() }
-    val participantGrid =
-        remember(event, presences) {
-            buildParticipantGrid(
-                participants = event.participants(),
-                presences = presences,
-            )
-        }
     // Tie the action bar's "am I on stage" gate to the same data
     // source the StageGrid uses (role + presence.onstage flag),
     // not just the kind-30312 role tag. Otherwise a host who taps
@@ -162,6 +153,10 @@ internal fun NestFullScreen(
         remember(participantGrid, myPubkey) {
             participantGrid.onStage.any { it.pubkey == myPubkey }
         }
+    val onStageKeys =
+        remember(participantGrid) {
+            participantGrid.onStage.map { it.pubkey }.toSet()
+        }
     // Same logic HandRaiseQueueSection uses internally — duplicated
     // here so the tab label can show a count without coupling the
     // section to the screen.

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

@@ -53,10 +53,10 @@ import com.vitorpamplona.amethyst.commons.viewmodels.BroadcastUiState
 import com.vitorpamplona.amethyst.commons.viewmodels.ConnectionUiState
 import com.vitorpamplona.amethyst.commons.viewmodels.NestUiState
 import com.vitorpamplona.amethyst.commons.viewmodels.NestViewModel
+import com.vitorpamplona.amethyst.commons.viewmodels.RoomMember
 import com.vitorpamplona.amethyst.ui.note.ClickableUserPicture
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.amethyst.ui.stringRes
-import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ParticipantTag
 
 /**
  * Compact PIP layout. Renders three things, in priority order:
@@ -84,7 +84,7 @@ import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ParticipantTa
 @Composable
 internal fun NestPipScreen(
     title: String?,
-    onStage: List<ParticipantTag>,
+    onStage: List<RoomMember>,
     ui: NestUiState,
     viewModel: NestViewModel,
     handRaised: Boolean,
@@ -97,7 +97,7 @@ internal fun NestPipScreen(
     // with the speakingNow set and produce ghost avatars.
     val onStageNowSpeaking =
         remember(onStage, ui.speakingNow) {
-            onStage.filter { it.pubKey in ui.speakingNow }
+            onStage.filter { it.pubkey in ui.speakingNow }
         }
     val focused =
         if (onStageNowSpeaking.isNotEmpty()) {
@@ -143,11 +143,11 @@ internal fun NestPipScreen(
             ) {
                 focused.forEach { participant ->
                     PipAvatar(
-                        pubkey = participant.pubKey,
+                        pubkey = participant.pubkey,
                         size = avatarSize,
-                        isSpeaking = participant.pubKey in ui.speakingNow,
+                        isSpeaking = participant.pubkey in ui.speakingNow,
-                        isConnecting = participant.pubKey in ui.connectingSpeakers,
+                        isConnecting = participant.pubkey in ui.connectingSpeakers,
-                        audioLevel = audioLevels[participant.pubKey] ?: 0f,
+                        audioLevel = audioLevels[participant.pubkey] ?: 0f,
                         accountViewModel = accountViewModel,
                     )
                 }

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/viewmodels/ParticipantGrid.kt

@@ -21,6 +21,8 @@
 package com.vitorpamplona.amethyst.commons.viewmodels
 
 import androidx.compose.runtime.Immutable
+import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ParticipantTag
 import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ROLE
 
 /**
@@ -70,16 +72,33 @@ data class ParticipantGrid(
  *   * Audience: every pubkey with recent presence that isn't on
  *     stage, plus participant-tagged users who haven't emitted
  *     presence yet (rendered as `absent = true`).
+ *
+ * [hostPubkey] is the kind-30312 event signer. Per the EGG-07
+ * convention (and nostrnests' production behaviour), the room
+ * author is the implicit host even when they don't self-tag.
+ * When the author isn't already in [participants], a synthetic
+ * `["p", hostPubkey, "", "host"]` tag is prepended so the
+ * presence-aware on-stage/audience rules apply uniformly —
+ * including the "host stepped off stage" case (presence with
+ * `onstage=0` → drops to audience, role stays HOST).
  */
 fun buildParticipantGrid(
-    participants: List<com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ParticipantTag>,
+    participants: List<ParticipantTag>,
     presences: Map<String, RoomPresence>,
+    hostPubkey: HexKey? = null,
 ): ParticipantGrid {
+    val effectiveParticipants =
+        if (hostPubkey != null && participants.none { it.pubKey == hostPubkey }) {
+            listOf(ParticipantTag(hostPubkey, null, ROLE.HOST.code, null)) + participants
+        } else {
+            participants
+        }
+
     val onStage = mutableListOf<RoomMember>()
     val audience = mutableListOf<RoomMember>()
 
     val seen = mutableSetOf<String>()
-    for (p in participants) {
+    for (p in effectiveParticipants) {
         seen += p.pubKey
         val pres = presences[p.pubKey]
         val role = p.effectiveRole()

commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/viewmodels/ParticipantGridTest.kt

@@ -115,4 +115,70 @@ class ParticipantGridTest {
         assertEquals(0, grid.onStage.size)
         assertEquals(0, grid.audience.size)
     }
+
+    @Test
+    fun implicitHostNotInPTagsLandsOnStage() {
+        // nostrnests publishes kind-30312 with no self-`p`-tag for
+        // the room author — the author is the implicit host. Without
+        // synthesizing them, they fell through into the pure-audience
+        // branch (role=null) AND were left out of the audio
+        // subscription set, producing "host shown in audience + no
+        // sound" — the exact regression this case exists to catch.
+        val grid =
+            buildParticipantGrid(
+                participants = listOf(pTag(speaker, ROLE.SPEAKER)),
+                presences = emptyMap(),
+                hostPubkey = host,
+            )
+        val hostRow = grid.onStage.firstOrNull { it.pubkey == host }
+        assertEquals(ROLE.HOST, hostRow?.role)
+        // No presence yet — host shows up greyed-out, matching how
+        // p-tagged speakers without presence already render.
+        assertEquals(true, hostRow?.absent)
+        assertTrue(grid.audience.none { it.pubkey == host })
+    }
+
+    @Test
+    fun implicitHostWithOnstageTrueStaysOnStage() {
+        val grid =
+            buildParticipantGrid(
+                participants = listOf(pTag(speaker, ROLE.SPEAKER)),
+                presences = mapOf(host to presence(host, 100L, onstage = true)),
+                hostPubkey = host,
+            )
+        val hostRow = grid.onStage.firstOrNull { it.pubkey == host }
+        assertEquals(ROLE.HOST, hostRow?.role)
+        assertEquals(false, hostRow?.absent)
+    }
+
+    @Test
+    fun implicitHostLeavesStageDropsToAudienceKeepingHostRole() {
+        // The host taps "Leave Stage" on nostrnests → kind-10312 with
+        // onstage=0. They should drop to audience but the host crown
+        // stays — exact same behaviour as an explicit speaker stepping
+        // off the stage.
+        val grid =
+            buildParticipantGrid(
+                participants = listOf(pTag(speaker, ROLE.SPEAKER)),
+                presences = mapOf(host to presence(host, 100L, onstage = false)),
+                hostPubkey = host,
+            )
+        assertTrue(grid.onStage.none { it.pubkey == host })
+        val hostRow = grid.audience.firstOrNull { it.pubkey == host }
+        assertEquals(ROLE.HOST, hostRow?.role)
+    }
+
+    @Test
+    fun explicitHostInPTagsIsNotDuplicated() {
+        // The author already tagged themselves with role=host. The
+        // synthesized entry must NOT shadow / duplicate them.
+        val grid =
+            buildParticipantGrid(
+                participants = listOf(pTag(host, ROLE.HOST), pTag(speaker, ROLE.SPEAKER)),
+                presences = mapOf(host to presence(host, 100L)),
+                hostPubkey = host,
+            )
+        assertEquals(2, grid.onStage.size)
+        assertEquals(1, grid.onStage.count { it.pubkey == host })
+    }
 }