feat(nests): back gesture and Minimize button enter PiP instead of leaving

The only way to keep audio playing while leaving the room screen was the
Home/Recents gesture (onUserLeaveHint). Back swiped the user out of the
session entirely, and there was no in-UI affordance signalling that PiP
existed. Users wanting to step away had no obvious path that preserved
audio.

- BackHandler in NestActivityContent: while connected and PIP is
  supported, back minimizes to PIP. Disconnected/Connecting/Failed
  fall through to the default finish() so cancelling still works.
- Minimize IconButton in the room TopAppBar (hidden when the device
  doesn't advertise FEATURE_PICTURE_IN_PICTURE).
- Public NestActivity.enterPip() consolidates the connected + feature
  guards so onUserLeaveHint, BackHandler, and the Minimize button all
  share one entry point.

https://claude.ai/code/session_01BpwAxN9gs79CJuWKqf3BEB

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

@@ -133,12 +133,16 @@ class NestActivity : AppCompatActivity() {
             registerReceiver(pipReceiver, filter)
         }
 
+        val pipSupported =
+            packageManager.hasSystemFeature(android.content.pm.PackageManager.FEATURE_PICTURE_IN_PICTURE)
+
         setContent {
             AmethystTheme {
                 NestActivityContent(
                     addressValue = addressValue,
                     accountViewModel = accountViewModel,
                     isInPipMode = isInPipMode.value,
+                    isPipSupported = pipSupported,
                     onMuteState = { muted ->
                         if (isMuted.value != muted) {
                             isMuted.value = muted
@@ -148,6 +152,7 @@ class NestActivity : AppCompatActivity() {
                     onConnectedChange = { isConnected.value = it },
                     pipMuteSignal = toggleMuteSignal,
                     onLeave = { finish() },
+                    onMinimize = { enterPip() },
                 )
             }
         }
@@ -155,9 +160,19 @@ class NestActivity : AppCompatActivity() {
 
     override fun onUserLeaveHint() {
         super.onUserLeaveHint()
-        // PIP only makes sense once the audio session is live; entering
+        enterPip()
-        // PIP from the lobby/Connecting state would freeze a half-rendered
+    }
-        // card in Recents. Also gates on the system supporting PIP.
+
+    /**
+     * Enter Picture-in-Picture if the audio session is live and the
+     * system supports PIP. Called both by [onUserLeaveHint] (Home /
+     * Recents gesture) and by user-driven entry points (back gesture,
+     * Minimize button in [com.vitorpamplona.amethyst.ui.screen.loggedIn.nests.room.screen.NestFullScreen]).
+     *
+     * Gated on `isConnected` so PIP from the lobby/Connecting state
+     * doesn't freeze a half-rendered card in Recents.
+     */
+    fun enterPip() {
         if (!isConnected.value) return
         if (!packageManager.hasSystemFeature(android.content.pm.PackageManager.FEATURE_PICTURE_IN_PICTURE)) return
         runCatching { enterPictureInPictureMode(buildPipParams()) }

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

@@ -20,6 +20,7 @@
  */
 package com.vitorpamplona.amethyst.ui.screen.loggedIn.nests.room.activity
 
+import androidx.activity.compose.BackHandler
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
@@ -28,6 +29,7 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.saveable.rememberSaveable
 import androidx.compose.runtime.setValue
 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.service.relayClient.reqCommand.event.observeNoteEvent
 import com.vitorpamplona.amethyst.ui.note.LoadAddressableNote
@@ -58,10 +60,12 @@ internal fun NestActivityContent(
     addressValue: String,
     accountViewModel: AccountViewModel,
     isInPipMode: Boolean,
+    isPipSupported: Boolean,
     onMuteState: (Boolean) -> Unit,
     onConnectedChange: (Boolean) -> Unit,
     pipMuteSignal: SharedFlow<Unit>,
     onLeave: () -> Unit,
+    onMinimize: () -> Unit,
 ) {
     val parsedAddress = remember(addressValue) { Address.parse(addressValue) }
     if (parsedAddress == null) {
@@ -97,10 +101,12 @@ internal fun NestActivityContent(
                     viewModel = viewModel,
                     accountViewModel = accountViewModel,
                     isInPipMode = isInPipMode,
+                    isPipSupported = isPipSupported,
                     onMuteState = onMuteState,
                     onConnectedChange = onConnectedChange,
                     pipMuteSignal = pipMuteSignal,
                     onLeave = onLeave,
+                    onMinimize = onMinimize,
                 )
             }
         }
@@ -125,10 +131,12 @@ private fun NestActivityBody(
     viewModel: NestViewModel,
     accountViewModel: AccountViewModel,
     isInPipMode: Boolean,
+    isPipSupported: Boolean,
     onMuteState: (Boolean) -> Unit,
     onConnectedChange: (Boolean) -> Unit,
     pipMuteSignal: SharedFlow<Unit>,
     onLeave: () -> Unit,
+    onMinimize: () -> Unit,
 ) {
     val account = accountViewModel.account
     val localPubkey = account.signer.pubKey
@@ -177,6 +185,13 @@ private fun NestActivityBody(
         handRaised = handRaised,
     )
 
+    // Back gesture while connected = minimize to PIP rather than tearing
+    // down the audio session. When disconnected (lobby / Connecting /
+    // Failed) or PIP isn't supported, we let back fall through to the
+    // default Activity.finish() so the user can cancel out cleanly.
+    val canMinimize = isPipSupported && !isInPipMode && ui.connection is ConnectionUiState.Connected
+    BackHandler(enabled = canMinimize) { onMinimize() }
+
     if (isInPipMode) {
         NestPipScreen(
             title = event.room(),
@@ -195,6 +210,8 @@ private fun NestActivityBody(
             handRaised = handRaised,
             onHandRaisedChange = { handRaised = it },
             onLeave = onLeave,
+            onMinimize = onMinimize,
+            canMinimize = isPipSupported,
         )
     }
 }

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

@@ -114,6 +114,8 @@ internal fun NestFullScreen(
     handRaised: Boolean,
     onHandRaisedChange: (Boolean) -> Unit,
     onLeave: () -> Unit,
+    onMinimize: () -> Unit,
+    canMinimize: Boolean,
 ) {
     var showEditSheet by rememberSaveable { mutableStateOf(false) }
     var showHostMenu by rememberSaveable { mutableStateOf(false) }
@@ -181,6 +183,8 @@ internal fun NestFullScreen(
                 title = event.room().orEmpty(),
                 isHost = isHost,
                 showHostMenu = showHostMenu,
+                showMinimize = canMinimize,
+                onMinimize = onMinimize,
                 onMenuOpen = { showHostMenu = true },
                 onMenuDismiss = { showHostMenu = false },
                 onShare = {
@@ -483,6 +487,8 @@ private fun NestTopAppBar(
     title: String,
     isHost: Boolean,
     showHostMenu: Boolean,
+    showMinimize: Boolean,
+    onMinimize: () -> Unit,
     onMenuOpen: () -> Unit,
     onMenuDismiss: () -> Unit,
     onShare: () -> Unit,
@@ -497,6 +503,18 @@ private fun NestTopAppBar(
             )
         },
         actions = {
+            // Minimize-to-PIP affordance. The user-facing way to learn
+            // that audio keeps playing in a floating window — pairs
+            // with the back-gesture handler in NestActivityContent.
+            // Hidden when the device doesn't advertise the PIP feature.
+            if (showMinimize) {
+                IconButton(onClick = onMinimize) {
+                    Icon(
+                        symbol = MaterialSymbols.PictureInPicture,
+                        contentDescription = stringRes(R.string.nest_minimize_description),
+                    )
+                }
+            }
             Box {
                 IconButton(onClick = onMenuOpen) {
                     Icon(

amethyst/src/main/res/values/strings.xml

@@ -584,6 +584,8 @@
     <string name="nest_participant_mute">Mute</string>
     <string name="nest_participant_unmute">Unmute</string>
     <string name="nest_share_action">Share room</string>
+    <string name="nest_minimize">Minimize</string>
+    <string name="nest_minimize_description">Minimize to keep listening</string>
     <string name="nest_create_fab">Start space</string>
     <string name="nest_no_server_title">Set up a nest server</string>
     <string name="nest_no_server_body">You haven\'t picked a nest server yet. Add %1$s to your server list and continue?\n\nYou can change this later in Settings.</string>