fix: studio save, memory and storage issues in multitrack recording

src/main/java/net/tfminecraft/musicalinstruments/InstrumentPlugin.java

@@ -69,7 +69,7 @@ public void onEnable() {
         getCommand("music").setExecutor(musicCommand);
         getCommand("music").setTabCompleter(musicCommand);
         getServer().getPluginManager().registerEvents(studioMenu, this);
-        getServer().getPluginManager().registerEvents(new StudioListener(studio, studioMenu), this);
+        getServer().getPluginManager().registerEvents(new StudioListener(this, studio, studioMenu), this);
 
         InstrumentCommand commandHandler = new InstrumentCommand(this, manager);
         getCommand("instruments").setExecutor(commandHandler);

src/main/java/net/tfminecraft/musicalinstruments/studio/Note.java

@@ -1,10 +1,14 @@
 package net.tfminecraft.musicalinstruments.studio;
 
+import java.util.regex.Pattern;
+
 /** A resolved sample trigger, captured independently of subsequent config changes. */
 public record Note(int tick, String instrument, String sound, float volume, float pitch) {
+    private static final Pattern SOUND = Pattern.compile("[a-z0-9_.-]+(:[a-z0-9_./-]+)?");
+
     public Note {
         if (tick < 0 || tick >= Song.MAX_TICKS || instrument == null || instrument.length() > 100
-                || sound == null || sound.length() > 200 || !sound.matches("[a-z0-9_.-]+(:[a-z0-9_./-]+)?")
+                || sound == null || sound.length() > 200 || !SOUND.matcher(sound).matches()
                 || !Float.isFinite(volume) || volume < 0 || volume > 16
                 || !Float.isFinite(pitch) || pitch < 0.5f || pitch > 2) {
             throw new IllegalArgumentException("Invalid recorded note");

src/main/java/net/tfminecraft/musicalinstruments/studio/Project.java

@@ -6,6 +6,10 @@ public record Project(Song song, Track pending, int bpm, boolean metronome) {
             throw new IllegalArgumentException("Tempo must be between 40 and 240 BPM");
         }
         if (pending != null) {
+            // A take uses its track's current mix. Without a saved track, as after removing it, the
+            // take is kept at full volume like one recorded on an empty track.
+            Track saved = song.track(pending.slot());
+            pending = saved != null ? pending.mix(saved.gain(), saved.muted()) : pending.mix(1, false);
             song.replace(pending); // Validate the prospective mix, including its total note bound.
         }
     }

src/main/java/net/tfminecraft/musicalinstruments/studio/ProjectSummary.java

@@ -0,0 +1,22 @@
+package net.tfminecraft.musicalinstruments.studio;
+
+import java.util.Comparator;
+import java.util.Objects;
+import java.util.UUID;
+
+/** What the project library shows, without loading a project's notes. */
+public record ProjectSummary(UUID id, String title, int tracks, int lengthTicks, int pendingSlot) {
+    public static final Comparator<ProjectSummary> ORDER = Comparator.comparing(ProjectSummary::title,
+            String.CASE_INSENSITIVE_ORDER).thenComparing(ProjectSummary::id);
+
+    public ProjectSummary {
+        Objects.requireNonNull(id);
+        Objects.requireNonNull(title);
+    }
+
+    public static ProjectSummary of(Project project) {
+        Song song = project.song();
+        return new ProjectSummary(song.id(), song.title(), song.tracks().size(), song.lengthTicks(),
+                project.pending() == null ? 0 : project.pending().slot());
+    }
+}

src/main/java/net/tfminecraft/musicalinstruments/studio/Song.java

@@ -41,6 +41,23 @@ public Track track(int slot) {
         return tracks.stream().filter(track -> track.slot() == slot).findFirst().orElse(null);
     }
 
+    /** Whether playback emits any sound; matches the notes {@link Timeline} schedules. */
+    public boolean audible() {
+        return tracks.stream().anyMatch(track -> !track.muted() && track.gain() > 0
+                && track.notes().stream().anyMatch(note -> note.volume() > 0));
+    }
+
+    /** The same song with only what playback emits: muted, silent and empty tracks and silent notes are left out. */
+    public Song audibleMix() {
+        List<Track> audible = new ArrayList<>();
+        for (Track track : tracks) {
+            if (track.muted() || track.gain() <= 0) continue;
+            List<Note> notes = track.notes().stream().filter(note -> note.volume() > 0).toList();
+            if (!notes.isEmpty()) audible.add(new Track(track.slot(), track.lengthTicks(), track.gain(), false, notes));
+        }
+        return new Song(id, owner, author, title, audible);
+    }
+
     public Song replace(Track track) {
         List<Track> result = new ArrayList<>(tracks);
         result.removeIf(existing -> existing.slot() == track.slot());
@@ -52,8 +69,4 @@ public Song replace(Track track) {
     public Song remove(int slot) {
         return new Song(id, owner, author, title, tracks.stream().filter(t -> t.slot() != slot).toList());
     }
-
-    public Song edition() {
-        return new Song(UUID.randomUUID(), owner, author, title, tracks);
-    }
 }

src/main/java/net/tfminecraft/musicalinstruments/studio/StudioCommand.java

@@ -56,7 +56,7 @@ public boolean onCommand(CommandSender sender, Command command, String label, St
                 case "projects" -> {
                     var projects = studio.listProjects(player);
                     if (projects.isEmpty()) player.sendMessage("No projects yet. Open /music studio to create a song.");
-                    for (Project project : projects) player.sendMessage(project.song().title() + " | " + project.song().id());
+                    for (ProjectSummary project : projects) player.sendMessage(project.title() + " | " + project.id());
                 }
                 case "open" -> {
                     need(args, 2, "open <project-id>");

src/main/java/net/tfminecraft/musicalinstruments/studio/StudioListener.java

@@ -11,21 +11,25 @@
 import org.bukkit.event.block.Action;
 import org.bukkit.event.block.BlockBreakEvent;
 import org.bukkit.event.inventory.InventoryMoveItemEvent;
+import org.bukkit.event.inventory.InventoryType;
 import org.bukkit.event.player.PlayerInteractEntityEvent;
 import org.bukkit.event.player.PlayerInteractEvent;
 import org.bukkit.event.player.PlayerQuitEvent;
 import org.bukkit.event.world.ChunkUnloadEvent;
 import org.bukkit.event.world.WorldUnloadEvent;
 import org.bukkit.inventory.EquipmentSlot;
 import org.bukkit.inventory.ItemStack;
+import org.bukkit.plugin.Plugin;
 
 import java.io.IOException;
 
 public final class StudioListener implements Listener {
+    private final Plugin plugin;
     private final StudioService studio;
     private final StudioMenu menu;
 
-    public StudioListener(StudioService studio, StudioMenu menu) {
+    public StudioListener(Plugin plugin, StudioService studio, StudioMenu menu) {
+        this.plugin = plugin;
         this.studio = studio;
         this.menu = menu;
     }
@@ -34,6 +38,8 @@ public StudioListener(StudioService studio, StudioMenu menu) {
     public void interact(PlayerInteractEvent event) {
         if (event.getAction() != Action.RIGHT_CLICK_BLOCK || event.getClickedBlock() == null
                 || event.useInteractedBlock() == Event.Result.DENY
+                // Check the type first: getState() copies block entities such as chest inventories.
+                || event.getClickedBlock().getType() != Material.JUKEBOX
                 || !(event.getClickedBlock().getState() instanceof Jukebox box)) {
             return;
         }
@@ -128,6 +134,25 @@ public void hopper(InventoryMoveItemEvent event) {
         }
     }
 
+    @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
+    public void extract(InventoryMoveItemEvent event) {
+        // A rejected transfer restores the source disc after the event, so check on the next tick.
+        // Hoppers move items constantly, so the cheap item and inventory type checks come first.
+        if (studio.discs().custom(event.getItem()) && event.getSource().getType() == InventoryType.JUKEBOX
+                && event.getSource().getLocation() != null) {
+            Block block = event.getSource().getLocation().getBlock();
+            plugin.getServer().getScheduler().runTask(plugin, () -> {
+                // Do not reload a chunk that unloaded while the transfer completed.
+                if (block.getWorld().isChunkLoaded(block.getX() >> 4, block.getZ() >> 4)
+                        && block.getType() == Material.JUKEBOX
+                        && block.getState() instanceof Jukebox box
+                        && !studio.discs().custom(box.getRecord())) {
+                    studio.stop(block);
+                }
+            });
+        }
+    }
+
     @EventHandler
     public void quit(PlayerQuitEvent event) {
         studio.quit(event.getPlayer());

src/main/java/net/tfminecraft/musicalinstruments/studio/StudioMenu.java

@@ -88,16 +88,16 @@ private void render(Player player, Holder holder) throws IOException {
     }
 
     private void renderLibrary(Player player, Holder holder) throws IOException {
-        List<Project> projects = studio.listProjects(player);
+        List<ProjectSummary> projects = studio.listProjects(player);
         inventoryItem(holder, 4, Material.BOOKSHELF, "Your songs", NamedTextColor.GOLD,
                 projects.size() + "/36 projects", "Left-click to open a song.", "Right-click to delete a song after confirmation.");
         for (int index = 0; index < Math.min(projects.size(), StudioService.MAX_PROJECTS); index++) {
-            Project project = projects.get(index);
+            ProjectSummary project = projects.get(index);
             int slot = 9 + index;
-            holder.choices.put(slot, project.song().id());
-            inventoryItem(holder, slot, Material.MUSIC_DISC_13, project.song().title(), NamedTextColor.YELLOW,
-                    project.song().tracks().size() + " tracks | " + time(project.song().lengthTicks()),
-                    project.pending() == null ? "No pending take" : "Pending take on track " + project.pending().slot(),
+            holder.choices.put(slot, project.id());
+            inventoryItem(holder, slot, Material.MUSIC_DISC_13, project.title(), NamedTextColor.YELLOW,
+                    project.tracks() + " tracks | " + time(project.lengthTicks()),
+                    project.pendingSlot() == 0 ? "No pending take" : "Pending take on track " + project.pendingSlot(),
                     "Left-click: open this project.", "Right-click: delete with confirmation.");
         }
         if (projects.isEmpty()) inventoryItem(holder, 22, Material.WRITABLE_BOOK, "Your studio is empty", NamedTextColor.GOLD,