fix: off-by-one errors in playback

Author: schollz

internal/input/playback.go

@@ -154,17 +154,19 @@ func AdvancePlayback(m *model.Model) {
 			activeTrackCount++
 			log.Printf("DEBUG_SONG: Processing active track %d, ticksLeft=%d", track, m.SongPlaybackTicksLeft[track])
 
-			// Decrement ticks for this track
+			// Decrement ticks for this track if > 0
 			if m.SongPlaybackTicksLeft[track] > 0 {
 				m.SongPlaybackTicksLeft[track]--
 				log.Printf("Song track %d: %d ticks remaining", track, m.SongPlaybackTicksLeft[track])
 			}
 
-			// Only advance this track when its ticks reach 0
+			// Only advance when ticks reach 0
 			if m.SongPlaybackTicksLeft[track] > 0 {
 				continue
 			}
 
+			log.Printf("Song track %d: ticks exhausted, advancing", track)
+
 			// Now advance to next playable row for this track
 			if !advanceToNextPlayableRowForTrack(m, track) {
 				// Track finished, deactivate

internal/model/model.go

@@ -2179,8 +2179,9 @@ func (m *Model) LoadTicksLeftForTrack(track int) {
 	if dtValue <= 0 {
 		m.SongPlaybackTicksLeft[track] = 0
 	} else {
-		// Set to dtValue - 1 because row was already emitted during initialization/advancement
-		m.SongPlaybackTicksLeft[track] = dtValue - 1
+		// Set to dtValue so the row plays for exactly DT ticks
+		// The playback logic will decrement on the LAST tick and then advance
+		m.SongPlaybackTicksLeft[track] = dtValue
 	}
 }