fix(android): interpolate UPnP position between polls + suppress post-seek race

android/app/src/main/java/com/fabledsword/minstrel/player/MinstrelForwardingPlayer.kt

@@ -3,6 +3,7 @@
 package com.fabledsword.minstrel.player
 
 import android.os.Handler
+import android.os.SystemClock
 import androidx.media3.common.ForwardingPlayer
 import androidx.media3.common.Player
 import com.fabledsword.minstrel.player.output.ActiveUpnp
@@ -59,6 +60,13 @@ class MinstrelForwardingPlayer(
     // bypasses the poll entirely via applyTransportPaused().
     @Volatile private var nonPlayingPollStreak = 0
 
+    // Wall-clock of the most-recent within-track seek we issued to Sonos.
+    // pollOnce uses this to suppress position overwrites for SEEK_ACK_WINDOW_MS
+    // -- Sonos can take 1-2s to apply a Seek, and a poll landing inside that
+    // window reports the *old* position. Without the lockout the scrubber
+    // visibly jumps backwards immediately after a drag, then forwards again.
+    @Volatile private var lastSeekIssuedAtMs: Long = 0L
+
     init {
         scope.launch {
             holder.active.collect { active -> onActiveChanged(active) }
@@ -122,6 +130,7 @@ class MinstrelForwardingPlayer(
         if (active == null) {
             super.seekTo(positionMs)
         } else {
+            lastSeekIssuedAtMs = SystemClock.elapsedRealtime()
             remoteState.applyPositionInfo(
                 positionMs = positionMs,
                 durationMs = remoteState.durationMs,
@@ -288,8 +297,14 @@ class MinstrelForwardingPlayer(
      */
     private suspend fun pollOnce(active: ActiveUpnp) {
         val info = active.avTransport.getPositionInfo()
+        val now = SystemClock.elapsedRealtime()
+        val inSeekAckWindow = lastSeekIssuedAtMs > 0L &&
+            (now - lastSeekIssuedAtMs) < SEEK_ACK_WINDOW_MS
+        // Inside the seek-ack window, keep the optimistic position we wrote in
+        // seekTo -- the poll's reported position is stale until Sonos finishes
+        // processing the Seek SOAP. Other fields still refresh from the poll.
         remoteState.applyPositionInfo(
-            positionMs = info.relTimeMs,
+            positionMs = if (inSeekAckWindow) remoteState.positionMs else info.relTimeMs,
             durationMs = info.trackDurationMs,
             trackUri = info.trackUri,
             trackNumber = info.track,
@@ -336,5 +351,6 @@ class MinstrelForwardingPlayer(
     private companion object {
         const val POLL_INTERVAL_MS = 1_000L
         const val NON_PLAYING_CONFIRM = 2
+        const val SEEK_ACK_WINDOW_MS = 2_000L
     }
 }

android/app/src/main/java/com/fabledsword/minstrel/player/PlayerController.kt

@@ -5,6 +5,7 @@ import android.content.Context
 import android.os.Bundle
 import android.os.Handler
 import android.os.Looper
+import android.os.SystemClock
 import androidx.media3.common.MediaItem
 import androidx.media3.common.MediaMetadata
 import androidx.media3.common.Player
@@ -491,16 +492,14 @@ class PlayerController @Inject constructor(
         scope.launch(Dispatchers.Main.immediate) {
             while (isActive) {
                 delay(POSITION_POLL_INTERVAL_MS)
-                // When UPnP is active, MediaController's cached state is stale --
-                // remoteState.applyTransportPlaying() doesn't fire a Player.Listener
-                // event, so onEvents never refreshes isPlaying / positionMs from
-                // the wrapped player. Read directly from remoteState here so the
-                // play/pause toggle and scrubber reflect Sonos's actual state.
                 val upnpActive = activeUpnpHolder.active.value != null
                 val effectiveIsPlaying =
                     if (upnpActive) remoteState.isPlaying else controller.isPlaying
-                val effectivePosition =
-                    if (upnpActive) remoteState.positionMs else controller.currentPosition
+                val effectivePosition = if (upnpActive) {
+                    interpolatedRemotePosition(effectiveIsPlaying)
+                } else {
+                    controller.currentPosition
+                }
                 val current = uiStateInternal.value
                 val newPos = effectivePosition.coerceAtLeast(0)
                 val newDur = effectiveDuration(
@@ -523,6 +522,32 @@ class PlayerController @Inject constructor(
         }
     }
 
+    // ── Remote position interpolation state ──────────────────────────────
+    // remoteState.positionMs is only refreshed by ForwardingPlayer's 1Hz
+    // SOAP poll (and only when the round-trip completes -- screen-off WiFi
+    // sleep can stall it for many seconds). To keep the scrubber moving
+    // smoothly we anchor each fresh reading + an elapsed-realtime stamp;
+    // between updates we display anchor + elapsed when Sonos is playing.
+    // A real correction lands as soon as the next poll arrives.
+    @Volatile private var lastSeenRemotePositionMs: Long = -1L
+    @Volatile private var positionAnchorMs: Long = 0L
+    @Volatile private var positionAnchorAtRealtimeMs: Long = 0L
+
+    private fun interpolatedRemotePosition(isPlaying: Boolean): Long {
+        val raw = remoteState.positionMs
+        val now = SystemClock.elapsedRealtime()
+        if (raw != lastSeenRemotePositionMs) {
+            lastSeenRemotePositionMs = raw
+            positionAnchorMs = raw
+            positionAnchorAtRealtimeMs = now
+        }
+        return if (isPlaying) {
+            positionAnchorMs + (now - positionAnchorAtRealtimeMs)
+        } else {
+            positionAnchorMs
+        }
+    }
+
     /**
      * Bridges Media3's `ListenableFuture<MediaController>.buildAsync()`
      * to a suspend function without pulling in `kotlinx-coroutines-guava`