scrobble: send now playing once per track change

A track transition resets the player position, and the scrobble policy's restart heuristic (same song, position drops to ~0) then re-announced the track we just left and, when the new track's position jittered back to zero, announced it twice. Suppress the now-playing when the restart is the same song; the submission logic still resets so a genuine replay is scrobbled again.

app/src/main/kotlin/com/subtracks/playback/Scrobbler.kt

@@ -59,6 +59,7 @@ class ScrobblePolicy(
             item?.id != songId ||
                 (item != null && item.id == lastItemId && positionMs < previousPosition && positionMs <= RESTART_POSITION_MS)
         if (restarted) {
+            val sameSong = item != null && item.id == songId
             songId = item?.id
             lastItemId = null
             playedMs = 0
@@ -68,7 +69,7 @@ class ScrobblePolicy(
             if (item == null || !isPlaying) return null
             nowPlayingSent = true
             startedAt = now()
-            return Scrobble.NowPlaying(item.id)
+            return if (sameSong) null else Scrobble.NowPlaying(item.id)
         }
         lastPositionMs = positionMs
         lastItemId = item?.id

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

@@ -130,15 +130,46 @@ class ScrobblePolicyTest {
     }
 
     @Test
-    fun restartingTheSameTrackScrobblesAgain() {
+    fun restartingTheSameTrackResubmitsWithoutReannouncing() {
         val item = track(durationMs = 200_000)
         play(item, toPositionMs = 100_000)
         clock = 120_000L
         val repeat = play(item, toPositionMs = 100_000)
-        assertEquals(Scrobble.NowPlaying("s1"), repeat.first())
+        assertEquals(emptyList<Scrobble>(), repeat.filterIsInstance<Scrobble.NowPlaying>())
         assertEquals(Scrobble.Submission("s1", 120_000L), repeat.last())
     }
 
+    @Test
+    fun doesNotReannounceTheTrackItJustLeftWhenItsPositionResets() {
+        val events = mutableListOf<Scrobble>()
+        events += play(track(id = "s1"), toPositionMs = 100_000)
+        events +=
+            listOfNotNull(
+                policy.advance(track(id = "s1"), 200_000, isPlaying = true, positionMs = 0),
+                policy.advance(track(id = "s2"), 200_000, isPlaying = true, positionMs = 0),
+            )
+        assertEquals(
+            listOf(Scrobble.NowPlaying("s1"), Scrobble.Submission("s1", 1_000L), Scrobble.NowPlaying("s2")),
+            events,
+        )
+    }
+
+    @Test
+    fun doesNotReannounceWhenTheNewTracksPositionJittersBackToZero() {
+        val events = mutableListOf<Scrobble>()
+        events += play(track(id = "s1"), toPositionMs = 100_000)
+        events +=
+            listOfNotNull(
+                policy.advance(track(id = "s2"), 200_000, isPlaying = true, positionMs = 0),
+                policy.advance(track(id = "s2"), 200_000, isPlaying = true, positionMs = 500),
+                policy.advance(track(id = "s2"), 200_000, isPlaying = true, positionMs = 0),
+            )
+        assertEquals(
+            listOf(Scrobble.NowPlaying("s1"), Scrobble.Submission("s1", 1_000L), Scrobble.NowPlaying("s2")),
+            events,
+        )
+    }
+
     @Test
     fun aTransitionDoesNotReannounceTheNewTrackOnAStaleLowPosition() {
         val first = track(id = "s1")