Silence a backgrounded player, and rebuild zones when a layout is edited in place

Two more from #234, both Android-only.

1. "I closed the app and I can still hear the sound." Nothing in the Android lifecycle pauses a
   WebView, and MainActivity had no onStop at all, so a YouTube embed kept playing with the app in
   the background and the panel kept making noise with the app apparently closed. onStop rather
   than onPause: onPause also fires for a transient dialog or a permission prompt, and pausing
   playback for those would be a visible stutter on a wall. Pauses via the IFrame-API bridge that
   already exists for live mute, so returning to the foreground resumes in place instead of
   restarting the clip.

2. "I added 4 zones and they dont appear on the screen. I had 3 zones before and they appeared."
   The zone rebuild fired only when the layout ID changed. Editing a layout in place keeps its id,
   so setupZones never ran: the geometry stayed at three zones and only the assignments
   re-rendered into the old ones, which is why it took a force-stop to appear. The rebuild now also
   triggers on a signature of the zones themselves (id, position, size, z-index, type, fit).

Compiles clean; NOT yet verified on hardware — both need a device to prove, unlike the audio-on-
item-switch fix which was measured before and after on an emulator.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Uaeo9MvzKoyXuN6ZsbhtkL

android/app/src/main/java/com/remotedisplay/player/MainActivity.kt

@@ -575,8 +575,21 @@ class MainActivity : AppCompatActivity() {
                 }.sorted().joinToString("|")
                 val changed = assignmentSig != zoneManager?.lastAssignmentSig
 
+                // The ZONES themselves can change without the layout id changing — editing a layout
+                // in place (adding a 4th zone to a 3-zone layout) keeps the same id. Rebuilding only
+                // on an id change meant the new zone never appeared: the geometry stayed as it was
+                // and only the assignments re-rendered into the OLD zones, so the change looked like
+                // it had been ignored until the app was force-stopped. Reported on #234.
+                val zoneSig = (0 until layoutZones.length()).map { i ->
+                    val z = layoutZones.getJSONObject(i)
+                    "${z.optString("id")}:${z.optDouble("x_percent", -1.0)}:${z.optDouble("y_percent", -1.0)}:" +
+                        "${z.optDouble("width_percent", -1.0)}:${z.optDouble("height_percent", -1.0)}:" +
+                        "${z.optInt("z_index", 0)}:${z.optString("zone_type")}:${z.optString("fit_mode")}"
+                }.sorted().joinToString("|")
+                val zonesChanged = zoneSig != zoneManager?.lastZoneSig
+
                 com.remotedisplay.player.util.DebugLog.i("Player", "Layout: MULTI-ZONE (${layoutZones.length()} zones, layout=$layoutId), ${assignments.length()} assignments")
-                if (zoneManager?.hasZones() != true || layoutId != currentLayoutId) {
+                if (zoneManager?.hasZones() != true || layoutId != currentLayoutId || zonesChanged) {
                     Log.i("MainActivity", "Multi-zone layout with ${layoutZones.length()} zones (layout=$layoutId, was=$currentLayoutId)")
                     handler.post {
                         hideStatus()
@@ -587,6 +600,7 @@ class MainActivity : AppCompatActivity() {
                         zoneManager?.setupZones(layoutZones, layoutId)
                         zoneManager?.renderAssignments(assignments, config.serverUrl, contentCache, config.deviceId)
                         zoneManager?.lastAssignmentSig = assignmentSig
+                        zoneManager?.lastZoneSig = zoneSig
                     }
                 } else if (changed) {
                     Log.i("MainActivity", "Multi-zone assignments changed, re-rendering")
@@ -1287,6 +1301,22 @@ class MainActivity : AppCompatActivity() {
         )
     }
 
+    /**
+     * Nothing in the Android lifecycle pauses a WebView, so a YouTube embed kept playing with the
+     * app in the background and the panel kept making noise with the app "closed". Reported on
+     * #234. onStop (not onPause) is the right hook: onPause also fires for a transient dialog or a
+     * permission prompt, and pausing playback for those would be a visible stutter on a wall.
+     */
+    override fun onStop() {
+        super.onStop()
+        if (::mediaPlayer.isInitialized) mediaPlayer.onAppBackgrounded()
+    }
+
+    override fun onStart() {
+        super.onStart()
+        if (::mediaPlayer.isInitialized) mediaPlayer.onAppForegrounded()
+    }
+
     override fun onDestroy() {
         remoteStreaming = false
         // Kill the wall/group leader tick BEFORE releasing media. The Handler is on the main looper

android/app/src/main/java/com/remotedisplay/player/player/MediaPlayerManager.kt

@@ -209,13 +209,42 @@ class MediaPlayerManager(
     // would restart the video and flicker. Main thread only (WebView access).
     private fun setYoutubeMuted(muted: Boolean) {
         youtubeMuted = muted
-        val func = if (muted) "mute" else "unMute"
+        postYoutubeCommand(if (muted) "mute" else "unMute")
+    }
+
+    /** Send one IFrame-API command to the embed. Main thread only (WebView access). */
+    private fun postYoutubeCommand(func: String) {
         val js = "(function(){try{var f=document.querySelector('iframe');" +
             "if(f&&f.contentWindow){f.contentWindow.postMessage(" +
             "JSON.stringify({event:'command',func:'$func',args:[]}),'*');}}catch(e){}})()"
         youtubeWebView?.let { wv -> wv.post { try { wv.evaluateJavascript(js, null) } catch (_: Throwable) {} } }
     }
 
+    /**
+     * The app is going to the background. Stop making noise.
+     *
+     * A WebView keeps running when its Activity stops — nothing in the lifecycle pauses it — so a
+     * YouTube embed carried on playing with the app closed and the audio kept coming out of the
+     * panel: "I closed the app and I can still hear the sound... I force stop the app and then open
+     * again." A signage player that is not on screen must be silent.
+     *
+     * Pause rather than blank, so returning to the foreground resumes in place instead of
+     * restarting the clip. pauseTimers() is process-wide, which is fine here (one WebView) and is
+     * what actually stops the embed's own scripted playback.
+     */
+    fun onAppBackgrounded() {
+        if (currentType == MediaType.YOUTUBE) postYoutubeCommand("pauseVideo")
+        youtubeWebView?.let { wv -> wv.post { try { wv.onPause(); wv.pauseTimers() } catch (_: Throwable) {} } }
+        exoPlayer?.pause()
+    }
+
+    /** Back in the foreground: undo onAppBackgrounded. */
+    fun onAppForegrounded() {
+        youtubeWebView?.let { wv -> wv.post { try { wv.resumeTimers(); wv.onResume() } catch (_: Throwable) {} } }
+        if (currentType == MediaType.YOUTUBE) postYoutubeCommand("playVideo")
+        if (currentType == MediaType.VIDEO) exoPlayer?.play()
+    }
+
     // Fullscreen widget render (single-zone / "fullscreen" layouts). Reuses the
     // full-screen WebView; ZoneManager handles widgets in multi-zone layouts.
     fun showWidget(url: String) {

android/app/src/main/java/com/remotedisplay/player/player/ZoneManager.kt

@@ -51,6 +51,9 @@ class ZoneManager(
     var currentLayoutId: String? = null
         private set
     var lastAssignmentSig: String? = null
+    // Geometry of the zones currently built. Editing a layout in place keeps its id, so the id
+    // alone cannot tell "same layout, same zones" from "same layout, zones changed".
+    var lastZoneSig: String? = null
 
     // #74/#75: device-effective IANA timezone for per-item schedule evaluation.
     @Volatile private var effectiveTimezone: String? = null