keep the previous artwork visible and stop the neighbour flashing mid-swipe

Swipe-back now goes to the previous track (previousTrack) instead of restarting, so the previous peek stays visible past the restart threshold. The frozen strip only hands back once the live neighbour props match it, so a stale neighbour can no longer flash while the slide settles.

app/src/test/kotlin/com/subtracks/playback/PlaybackControllerTest.kt

@@ -213,7 +213,7 @@ class PlaybackControllerTest {
     }
 
     @Test
-    fun previousItemIsNullOncePreviousWouldRestartTheTrack() {
+    fun previousTrackMovesBackEvenOncePreviousWouldRestart() {
         seedAlbum(3, sourceId = 1)
         controller.playAlbum(1, "al1", 1)
         await {
@@ -222,8 +222,12 @@ class PlaybackControllerTest {
         }
 
         handle.positionMs = 3_100
+        controller.previousTrack()
 
-        assertNull(runBlocking { controller.previousItem() })
+        await {
+            controller.state.value.item
+                ?.id == "s1"
+        }
     }
 
     @Test

app/src/test/kotlin/com/subtracks/ui/playback/NowPlayingTapsTest.kt

@@ -56,6 +56,7 @@ class NowPlayingTapsTest {
         onArtistClick: (() -> Unit)? = null,
         onNext: () -> Unit = {},
         onPrevious: () -> Unit = {},
+        onSkipPrevious: () -> Unit = onPrevious,
         previousArt: NowPlayingArt? = null,
         nextArt: NowPlayingArt? = null,
     ) {
@@ -72,6 +73,7 @@ class NowPlayingTapsTest {
                     onPlayPause = {},
                     onNext = onNext,
                     onPrevious = onPrevious,
+                    onSkipPrevious = onSkipPrevious,
                     onAlbumClick = onAlbumClick,
                     onArtistClick = onArtistClick,
                     onSeek = {},
@@ -163,12 +165,34 @@ class NowPlayingTapsTest {
     fun swipingRightOnTheCoverGoesToThePreviousTrack() {
         var next = false
         var previous = false
-        render(onNext = { next = true }, onPrevious = { previous = true })
+        var skipPrevious = false
+        render(
+            onNext = { next = true },
+            onPrevious = { previous = true },
+            onSkipPrevious = { skipPrevious = true },
+        )
 
         composeRule.onNodeWithTag(NOW_PLAYING_COVER_TAG).performTouchInput { swipeRight() }
 
-        assertTrue("a right swipe should go to the previous track", previous)
+        assertTrue("a right swipe should skip to the previous track", skipPrevious)
         assertTrue("a right swipe should not skip to the next track", !next)
+        assertTrue("a right swipe should not use the restart-on-previous button", !previous)
+    }
+
+    @Test
+    fun theStripHandsBackOnlyWhenTheLivePropsAgree() {
+        val before = adjacentArt("s0")
+        val current = adjacentArt("s1")
+        val next = adjacentArt("s2")
+        val after = adjacentArt("s3")
+        val frozenNext = listOf(current, next, null)
+        val frozenPrevious = listOf(null, before, current)
+
+        assertTrue(!handBackReady(frozenNext, itemId = "s1", previousArt = before, nextArt = after))
+        assertTrue(!handBackReady(frozenNext, itemId = "s2", previousArt = before, nextArt = after))
+        assertTrue(handBackReady(frozenNext, itemId = "s2", previousArt = current, nextArt = after))
+        assertTrue(handBackReady(frozenPrevious, itemId = "s0", previousArt = null, nextArt = current))
+        assertTrue(!handBackReady(frozenPrevious, itemId = "s1", previousArt = null, nextArt = current))
     }
 
     @Test