Android player: video-wall (wall:sync) support

Ports the wall:sync protocol the web and Tizen players already ship to native
Kotlin/ExoPlayer, so the Android player can join a video wall.

- WallController (new): 4Hz leader broadcast; follower latency-compensated drift
  controller (hard-seek past 0.3s, gentle +/-3% playbackRate nudge past 0.05s);
  role handling with immediate align on entry and on wall:sync-request. Per-tile
  rotation intentionally not applied (web/Tizen parity; left as a TODO).
- MediaPlayerManager: expose position/duration/seekExact/setSpeed for the drift
  controller; RESIZE_MODE_FILL / ImageView FIT_XY in wall mode (object-fit:fill
  parity), restored to fit/fitCenter on exit. Follower mute (setWallMute) persists
  across leader-driven item switches, and followers loop (REPEAT_MODE_ONE) so they
  never freeze on the last frame if the leader's next index is late.
- PlaylistController: wallFollower flag suppresses auto-advance (leader drives the
  index); getIndex/gotoIndex for follower tracking; itemStartedAtMs for non-video
  sync position.
- WebSocketService: onWallSync/onWallSyncRequest handlers (posted to the main
  thread since they drive ExoPlayer) + emitWallSync/emitWallSyncRequest senders
  guarded on socket.connected() like sendPlaybackState.
- MainActivity: parse wall_config in onPlaylistUpdate and branch before the
  orientation + multi-zone paths; size/translate rootView to this screen's slice;
  exit() restores full screen.

Compiles clean (./gradlew :app:assembleDebug). NOT yet validated on a device or a
real wall — the ExoPlayer seek/speed sync and the slice transform need on-device
tuning before this is trusted.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -14,6 +14,7 @@ import android.os.Looper
 import android.util.Log
 import android.view.KeyEvent
 import android.view.View
+import android.view.ViewGroup
 import android.view.WindowManager
 import android.view.accessibility.AccessibilityManager
 import android.widget.ImageView
@@ -25,6 +26,7 @@ import com.remotedisplay.player.data.ServerConfig
 import com.remotedisplay.player.player.MediaPlayerManager
 import com.remotedisplay.player.player.PlaylistController
 import com.remotedisplay.player.player.PlaylistItem
+import com.remotedisplay.player.player.WallController
 import com.remotedisplay.player.player.ZoneManager
 import com.remotedisplay.player.remote.ScreenshotCapture
 import com.remotedisplay.player.remote.TouchInjector
@@ -46,6 +48,7 @@ class MainActivity : AppCompatActivity() {
     private lateinit var playlistController: PlaylistController
     private lateinit var updateChecker: UpdateChecker
     private var zoneManager: ZoneManager? = null
+    private lateinit var wallController: WallController
 
     private lateinit var playerView: PlayerView
     private lateinit var imageView: ImageView
@@ -157,6 +160,17 @@ class MainActivity : AppCompatActivity() {
             }
         )
 
+        // Video-wall controller. The emit lambdas read wsService lazily (it's bound after
+        // onCreate), and they no-op until the socket is connected (guarded in the service).
+        wallController = WallController(
+            media = mediaPlayer,
+            playlist = playlistController,
+            deviceId = { config.deviceId },
+            emitSync = { wallId, idx, contentId, posSec -> wsService?.emitWallSync(wallId, idx, contentId, posSec) },
+            emitSyncRequest = { wallId -> wsService?.emitWallSyncRequest(wallId) },
+            applyTransform = { cfg -> applyWallTransform(cfg) }
+        )
+
         // Restore cached playlist for offline cold-start (play immediately from disk cache).
         // Catch Throwable (not just Exception) so an OOM or corrupt entry can't kill the app
         // before the WebSocket connects — that's the crash-loop scenario. If the cache is
@@ -233,10 +247,75 @@ class MainActivity : AppCompatActivity() {
         Log.i("MainActivity", "Applied orientation: $orientation (rotation=$rot, swap=$swap)")
     }
 
+    private fun parseWallConfig(wc: JSONObject): WallController.WallConfig {
+        fun rect(key: String): WallController.Rect {
+            val o = wc.optJSONObject(key)
+            return WallController.Rect(
+                x = o?.optDouble("x", 0.0)?.toFloat() ?: 0f,
+                y = o?.optDouble("y", 0.0)?.toFloat() ?: 0f,
+                w = o?.optDouble("w", 0.0)?.toFloat() ?: 0f,
+                h = o?.optDouble("h", 0.0)?.toFloat() ?: 0f
+            )
+        }
+        return WallController.WallConfig(
+            wallId = wc.optString("wall_id", ""),
+            screen = rect("screen_rect"),
+            player = rect("player_rect"),
+            isLeader = wc.optBoolean("is_leader", false),
+            rotation = wc.optInt("rotation", 0)
+        )
+    }
+
+    // Video-wall slice transform. The content view represents the whole wall (player_rect);
+    // size + offset rootView so this screen's screen_rect fills the device viewport, content
+    // stretched to fill (object-fit:fill parity, set on the views via MediaPlayerManager).
+    // Mirrors the web player's vw/vh stage math. Per-tile rotation is intentionally not
+    // applied (web/Tizen parity). cfg == null restores full screen.
+    private fun applyWallTransform(cfg: WallController.WallConfig?) {
+        val lp = rootView.layoutParams
+        if (cfg == null) {
+            lp.width = ViewGroup.LayoutParams.MATCH_PARENT
+            lp.height = ViewGroup.LayoutParams.MATCH_PARENT
+            rootView.layoutParams = lp
+            rootView.translationX = 0f
+            rootView.translationY = 0f
+            rootView.rotation = 0f
+            rootView.scaleX = 1f
+            rootView.scaleY = 1f
+            rootView.requestLayout()
+            // Force the next playlist update to re-apply orientation (applyOrientation
+            // early-returns when the value is unchanged).
+            currentOrientation = null
+            Log.i("MainActivity", "Wall transform cleared (restored full screen)")
+            return
+        }
+        val s = cfg.screen
+        val p = cfg.player
+        if (s.w == 0f || s.h == 0f) {
+            Log.w("MainActivity", "Wall screen_rect has zero size; skipping transform")
+            return
+        }
+        val dw = resources.displayMetrics.widthPixels.toFloat()
+        val dh = resources.displayMetrics.heightPixels.toFloat()
+        lp.width = ((p.w / s.w) * dw).toInt()
+        lp.height = ((p.h / s.h) * dh).toInt()
+        rootView.layoutParams = lp
+        rootView.translationX = ((p.x - s.x) / s.w) * dw   // negative for right/lower tiles
+        rootView.translationY = ((p.y - s.y) / s.h) * dh
+        rootView.rotation = 0f                              // per-tile rotation: TODO (parity = none)
+        rootView.scaleX = 1f
+        rootView.scaleY = 1f
+        rootView.requestLayout()
+        // Orientation no longer reflects reality; ensure it re-applies after wall exit.
+        currentOrientation = null
+        Log.i("MainActivity", "Wall transform: size=${lp.width}x${lp.height} tx=${rootView.translationX} ty=${rootView.translationY}")
+    }
+
     private fun setupServiceCallbacks() {
         wsService?.onPlaylistUpdate = { data ->
             try {
-            applyOrientation(data.optString("orientation", "landscape"))
+            // Orientation is applied in the non-wall branch below; wall mode owns the
+            // root-view transform itself and must not be rotated.
             // Check if device is suspended (trial expired / over limit)
             if (data.optBoolean("suspended", false)) {
                 val message = data.optString("message", "Account Suspended")
@@ -257,6 +336,20 @@ class MainActivity : AppCompatActivity() {
             // Cache playlist JSON for offline cold-start
             config.cachedPlaylist = data.toString()
 
+            // Video-wall mode takes precedence over orientation + multi-zone: the wall is
+            // fullscreen, and WallController owns the root-view slice transform and the
+            // leader/follower role. (We're on the main thread here — onPlaylistUpdate is
+            // posted to the main looper by WebSocketService.)
+            val wallObj = if (data.isNull("wall_config")) null else data.optJSONObject("wall_config")
+            if (wallObj != null) {
+                com.remotedisplay.player.util.DebugLog.i("Player", "Layout: VIDEO-WALL (${assignments.length()} assignments)")
+                if (zoneManager?.hasZones() == true) zoneManager?.cleanup()
+                wallController.apply(parseWallConfig(wallObj))
+                playlistController.updatePlaylist(assignments)
+            } else {
+            wallController.exit()
+            applyOrientation(data.optString("orientation", "landscape"))
+
             // Check for multi-zone layout
             val layoutObj = if (data.isNull("layout")) null else data.optJSONObject("layout")
             val layoutZones = layoutObj?.optJSONArray("zones")
@@ -301,8 +394,11 @@ class MainActivity : AppCompatActivity() {
                 if (zoneManager?.hasZones() == true) handler.post { zoneManager?.cleanup() }
                 playlistController.updatePlaylist(assignments)
             }
+            } // end else (not a video wall)
 
-            // Download any missing local content (skip remote URLs)
+            // Download any missing local content (skip remote URLs).
+            // Runs for wall + single-zone; multi-zone drives its own rendering via ZoneManager
+            // (the startIfNeeded below is guarded so it won't run behind zones).
             thread {
                 for (i in 0 until assignments.length()) {
                     val item = assignments.getJSONObject(i)
@@ -451,6 +547,9 @@ class MainActivity : AppCompatActivity() {
             }
         }
 
+        wsService?.onWallSync = { data -> if (::wallController.isInitialized) wallController.onSync(data) }
+        wsService?.onWallSyncRequest = { data -> if (::wallController.isInitialized) wallController.onSyncRequest(data) }
+
         wsService?.onRegistered = { _ ->
             hideStatus()
         }

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

@@ -7,9 +7,12 @@ import android.webkit.WebChromeClient
 import android.webkit.WebView
 import android.webkit.WebViewClient
 import android.widget.ImageView
+import androidx.media3.common.C
 import androidx.media3.common.MediaItem
 import androidx.media3.common.Player
 import androidx.media3.exoplayer.ExoPlayer
+import androidx.media3.exoplayer.SeekParameters
+import androidx.media3.ui.AspectRatioFrameLayout
 import androidx.media3.ui.PlayerView
 import com.remotedisplay.player.util.ImageLoader
 import java.io.File
@@ -24,6 +27,9 @@ class MediaPlayerManager(
 ) {
     private var exoPlayer: ExoPlayer? = null
     private var currentType: MediaType = MediaType.NONE
+    // Wall mode: followers must stay muted even as the leader's sync switches them
+    // to a new (possibly unmuted) item, so the mute has to survive each playVideo.
+    private var wallMute = false
 
     enum class MediaType { NONE, VIDEO, IMAGE, YOUTUBE, WIDGET }
 
@@ -91,7 +97,7 @@ class MediaPlayerManager(
         youtubeWebView?.visibility = android.view.View.GONE
 
         exoPlayer?.apply {
-            volume = if (muted) 0f else 1f
+            volume = if (muted || wallMute) 0f else 1f
             setMediaItem(MediaItem.fromUri(Uri.parse(url)))
             prepare()
             playWhenReady = true
@@ -132,7 +138,7 @@ class MediaPlayerManager(
         youtubeWebView?.visibility = android.view.View.GONE
 
         exoPlayer?.apply {
-            volume = if (muted) 0f else 1f
+            volume = if (muted || wallMute) 0f else 1f
             setMediaItem(MediaItem.fromUri(Uri.fromFile(file)))
             prepare()
             playWhenReady = true
@@ -177,4 +183,55 @@ class MediaPlayerManager(
     }
 
     fun isPlayingVideo(): Boolean = currentType == MediaType.VIDEO && (exoPlayer?.isPlaying == true)
+
+    // ---- Video-wall (wall:sync) accessors. All must be called on the main thread. ----
+
+    /** Current video position in ms (0 when no video). */
+    fun currentPositionMs(): Long = exoPlayer?.currentPosition ?: 0L
+
+    /** Video duration in ms, or -1 when unknown/unprepared. */
+    fun durationMs(): Long {
+        val d = exoPlayer?.duration ?: C.TIME_UNSET
+        return if (d == C.TIME_UNSET) -1L else d
+    }
+
+    /** Exact (frame-accurate) seek for the follower drift controller's hard-seek path. */
+    fun seekExact(positionMs: Long) {
+        exoPlayer?.apply {
+            setSeekParameters(SeekParameters.EXACT)
+            seekTo(positionMs)
+        }
+    }
+
+    /** Playback rate — followers nudge ±3% to converge on the leader's clock. */
+    fun setSpeed(rate: Float) { exoPlayer?.setPlaybackSpeed(rate) }
+
+    /**
+     * Wall follower mute. Persists across item switches (the leader's sync can move a
+     * follower to an unmuted item, and N copies of the same audio out of phase flange),
+     * and enforces the mute on whatever is playing right now.
+     */
+    fun setWallMute(mute: Boolean) {
+        wallMute = mute
+        if (mute) exoPlayer?.volume = 0f
+    }
+
+    /**
+     * Loop the current video for wall followers so they never freeze on the last frame
+     * if the leader's next index sync is slightly late; the leader plays through normally.
+     */
+    fun setVideoLooping(loop: Boolean) {
+        exoPlayer?.repeatMode = if (loop) Player.REPEAT_MODE_ONE else Player.REPEAT_MODE_OFF
+    }
+
+    /**
+     * In wall mode the content fills its slice (object-fit:fill parity with the web/Tizen
+     * players); restore the default fit on exit.
+     */
+    fun setWallMode(enabled: Boolean) {
+        playerView.resizeMode =
+            if (enabled) AspectRatioFrameLayout.RESIZE_MODE_FILL else AspectRatioFrameLayout.RESIZE_MODE_FIT
+        imageView.scaleType =
+            if (enabled) ImageView.ScaleType.FIT_XY else ImageView.ScaleType.FIT_CENTER
+    }
 }

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

@@ -42,8 +42,32 @@ class PlaylistController(
     @Volatile private var effectiveTimezone: String? = null
     private var retryRunnable: Runnable? = null
 
+    // Video wall: followers don't self-advance — the leader's wall:sync drives the index.
+    private var wallFollower = false
+    // Wall-clock at which the current item started playing, for non-video sync position.
+    private var itemStartedAt = 0L
+
     val isPlaying: Boolean get() = isRunning && currentIndex >= 0
 
+    /** Video wall: true on followers (suppress auto-advance; leader drives the index). */
+    fun setWallFollower(b: Boolean) { wallFollower = b }
+
+    /** Current playlist index (-1 if nothing is playing). */
+    fun getIndex(): Int = currentIndex
+
+    /** Wall-clock ms when the current item started; used for non-video sync position. */
+    fun itemStartedAtMs(): Long = itemStartedAt
+
+    /** Jump to an absolute index (wraps); used by wall followers tracking the leader. */
+    fun gotoIndex(idx: Int) {
+        if (items.isEmpty()) return
+        val n = items.size
+        val target = ((idx % n) + n) % n
+        if (target == currentIndex) return
+        currentIndex = target
+        playCurrentItem()
+    }
+
     /** #74/#75: device-effective IANA timezone for per-item schedule evaluation. */
     fun setTimezone(tz: String?) { effectiveTimezone = tz }
 
@@ -187,7 +211,9 @@ class PlaylistController(
     }
 
     fun onVideoComplete() {
-        // Called when a video finishes naturally
+        // Called when a video finishes naturally. Wall followers don't self-advance —
+        // they hold (and loop) the leader's item until a wall:sync changes the index.
+        if (wallFollower) return
         next()
     }
 
@@ -195,12 +221,14 @@ class PlaylistController(
         cancelAdvance()
         cancelRetry()
         val item = currentItem ?: return
+        itemStartedAt = System.currentTimeMillis()
         Log.i("PlaylistController", "Playing: ${item.filename} (index $currentIndex)")
         onItemChanged(item)
 
         // For images and widgets, auto-advance after duration. For videos, wait
-        // for the completion callback.
-        if (item.mimeType.startsWith("image/") || item.isWidget) {
+        // for the completion callback. Wall followers never auto-advance — the
+        // leader's wall:sync index drives every switch.
+        if (!wallFollower && (item.mimeType.startsWith("image/") || item.isWidget)) {
             scheduleAdvance(item.durationSec * 1000L)
         }
     }

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

@@ -0,0 +1,143 @@
+package com.remotedisplay.player.player
+
+import android.os.Handler
+import android.os.Looper
+import android.util.Log
+import org.json.JSONObject
+import kotlin.math.abs
+
+/**
+ * Video-wall (`wall:sync`) controller. Native Kotlin/ExoPlayer port of the web player
+ * (`server/player/index.html`) and the Tizen `WallController` — same protocol, gates, and
+ * drift maths.
+ *
+ *  - Leader: plays normally and broadcasts `wall:sync` at 4Hz (plus an immediate align on
+ *    entry and on every `wall:sync-request`).
+ *  - Follower: never self-advances; switches item only when a `wall:sync` carries a new
+ *    `current_index`, and for video runs a latency-compensated drift controller that hard-
+ *    seeks on large drift and nudges playbackRate on small drift. Followers are muted.
+ *
+ * The slice view transform (sizing/translating the root view to this screen's tile) lives in
+ * MainActivity and is invoked through [applyTransform]. Per-tile `rotation` is intentionally
+ * not applied (web/Tizen parity — left as a TODO).
+ *
+ * All ExoPlayer/View touches happen on the main thread; the 4Hz timer runs on the main looper
+ * and `onSync` is delivered on the main thread by WebSocketService.
+ */
+class WallController(
+    private val media: MediaPlayerManager,
+    private val playlist: PlaylistController,
+    private val deviceId: () -> String,
+    private val emitSync: (wallId: String, idx: Int, contentId: String?, posSec: Float) -> Unit,
+    private val emitSyncRequest: (wallId: String) -> Unit,
+    private val applyTransform: (WallConfig?) -> Unit
+) {
+    data class Rect(val x: Float, val y: Float, val w: Float, val h: Float)
+    data class WallConfig(
+        val wallId: String,
+        val screen: Rect,
+        val player: Rect,
+        val isLeader: Boolean,
+        val rotation: Int
+    )
+
+    private val handler = Handler(Looper.getMainLooper())
+    private var config: WallConfig? = null
+    private var tick: Runnable? = null
+
+    val isActive: Boolean get() = config != null
+
+    /** Enter/refresh wall mode for the given config (idempotent; handles role flips). */
+    fun apply(cfg: WallConfig) {
+        config = cfg
+        Log.i("WallController", "apply wall=${cfg.wallId} isLeader=${cfg.isLeader}")
+
+        applyTransform(cfg)                       // size/translate the root view to our slice
+        media.setWallMode(true)                   // object-fit:fill parity
+        playlist.setWallFollower(!cfg.isLeader)   // followers don't self-advance
+        media.setWallMute(!cfg.isLeader)          // followers muted (avoid flange)
+        media.setVideoLooping(!cfg.isLeader)      // followers loop so they never freeze
+
+        stopTimer()
+        if (cfg.isLeader) {
+            tick = object : Runnable {
+                override fun run() { emitNow(); handler.postDelayed(this, 250) }
+            }
+            handler.postDelayed(tick!!, 250)
+            handler.postDelayed({ emitNow() }, 100)   // immediate first align
+        } else {
+            emitSyncRequest(cfg.wallId)               // align now, don't wait a tick
+        }
+    }
+
+    /** Leave wall mode and restore full-screen playback. */
+    fun exit() {
+        stopTimer()
+        val had = config != null
+        config = null
+        if (!had) return
+        Log.i("WallController", "exit wall mode")
+        playlist.setWallFollower(false)
+        media.setWallMute(false)
+        media.setVideoLooping(false)
+        media.setWallMode(false)
+        applyTransform(null)
+    }
+
+    private fun emitNow() {
+        val c = config ?: return
+        if (!c.isLeader) return
+        val item = playlist.currentItem ?: return
+        val pos = if (media.isPlayingVideo()) {
+            media.currentPositionMs() / 1000f
+        } else {
+            ((System.currentTimeMillis() - playlist.itemStartedAtMs()) / 1000f).coerceAtLeast(0f)
+        }
+        emitSync(c.wallId, playlist.getIndex(), item.contentId.ifEmpty { null }, pos)
+    }
+
+    /** Handle an incoming `wall:sync` (followers only). */
+    fun onSync(data: JSONObject) {
+        val c = config ?: return
+        if (c.isLeader) return
+        if (data.optString("wall_id") != c.wallId) return
+
+        val leaderIdx = data.optInt("current_index", -1)
+        if (leaderIdx >= 0 && leaderIdx != playlist.getIndex()) playlist.gotoIndex(leaderIdx)
+
+        if (!media.isPlayingVideo()) return       // images/widgets: index match is enough
+
+        val sentAt = data.optLong("sent_at", 0L)
+        val latency = if (sentAt > 0) ((System.currentTimeMillis() - sentAt) / 1000f).coerceAtLeast(0f) else 0f
+        val target = data.optDouble("position_sec", 0.0).toFloat() + latency
+        val curSec = media.currentPositionMs() / 1000f
+        val durMs = media.durationMs()
+        val durSec = if (durMs < 0) Float.NaN else durMs / 1000f
+        val drift = curSec - target
+        val ad = abs(drift)
+        when {
+            // Large drift: hard-seek (only when the target is within a known duration so we
+            // don't seek past the end). Don't seek every tick — exact seeks are expensive.
+            ad > 0.3f && !durSec.isNaN() && target < durSec -> {
+                media.seekExact((target * 1000).toLong())
+                media.setSpeed(1.0f)
+            }
+            // Small drift: gentle ±3% playbackRate nudge to converge.
+            ad > 0.05f -> media.setSpeed(if (drift > 0) 0.97f else 1.03f)
+            else -> media.setSpeed(1.0f)
+        }
+    }
+
+    /** Handle a follower's `wall:sync-request` (leader only): broadcast position now. */
+    fun onSyncRequest(data: JSONObject) {
+        val c = config ?: return
+        if (!c.isLeader) return
+        if (data.has("wall_id") && data.optString("wall_id") != c.wallId) return
+        emitNow()
+    }
+
+    private fun stopTimer() {
+        tick?.let { handler.removeCallbacks(it) }
+        tick = null
+    }
+}

android/app/src/main/java/com/remotedisplay/player/service/WebSocketService.kt

@@ -40,6 +40,8 @@ class WebSocketService : Service() {
     var onRemoteTouch: ((Float, Float, String) -> Unit)? = null
     var onRemoteKey: ((String) -> Unit)? = null
     var onCommand: ((String, JSONObject?) -> Unit)? = null
+    var onWallSync: ((JSONObject) -> Unit)? = null
+    var onWallSyncRequest: ((JSONObject) -> Unit)? = null
 
     inner class LocalBinder : Binder() {
         fun getService(): WebSocketService = this@WebSocketService
@@ -222,6 +224,18 @@ class WebSocketService : Service() {
                     handler.post { try { onRemoteKey?.invoke(keycode) } catch (e: Throwable) { Log.e("WebSocketService", "onRemoteKey cb: ${e.message}") } }
                 }
 
+                // Video wall. Post to the main thread: the handlers drive ExoPlayer
+                // (seek/speed/position), which is main-thread-only.
+                safeOn("wall:sync") { args ->
+                    val data = args.firstOrNull() as? JSONObject ?: return@safeOn
+                    handler.post { try { onWallSync?.invoke(data) } catch (e: Throwable) { Log.e("WebSocketService", "onWallSync cb: ${e.message}") } }
+                }
+
+                safeOn("wall:sync-request") { args ->
+                    val data = args.firstOrNull() as? JSONObject ?: return@safeOn
+                    handler.post { try { onWallSyncRequest?.invoke(data) } catch (e: Throwable) { Log.e("WebSocketService", "onWallSyncRequest cb: ${e.message}") } }
+                }
+
                 safeOn("device:command") { args ->
                     val data = args.firstOrNull() as? JSONObject ?: return@safeOn
                     val type = data.optString("type", "")
@@ -525,6 +539,29 @@ class WebSocketService : Service() {
         } catch (e: Throwable) { Log.w("WebSocketService", "sendPlaybackState: ${e.message}") }
     }
 
+    // Video-wall senders. Guarded on socket.connected() like sendPlaybackState, so a
+    // pre-register tick is a no-op (the server would reject it as unauthenticated).
+    fun emitWallSync(wallId: String, currentIndex: Int, contentId: String?, positionSec: Float) {
+        if (socket?.connected() != true) return
+        try {
+            socket?.emit("wall:sync", JSONObject().apply {
+                put("wall_id", wallId)
+                put("device_id", config.deviceId)
+                put("current_index", currentIndex)
+                put("content_id", contentId ?: JSONObject.NULL)
+                put("position_sec", positionSec.toDouble())
+                put("sent_at", System.currentTimeMillis())
+            })
+        } catch (e: Throwable) { Log.w("WebSocketService", "emitWallSync: ${e.message}") }
+    }
+
+    fun emitWallSyncRequest(wallId: String) {
+        if (socket?.connected() != true) return
+        try {
+            socket?.emit("wall:sync-request", JSONObject().apply { put("wall_id", wallId) })
+        } catch (e: Throwable) { Log.w("WebSocketService", "emitWallSyncRequest: ${e.message}") }
+    }
+
     fun disconnect() {
         stopHeartbeat()
         try { socket?.disconnect() } catch (e: Throwable) { Log.w("WebSocketService", "disconnect: ${e.message}") }