[thcp]

Summary

Fixes drag-and-drop of tracks to library folders not working on the Windows desktop app.

Root cause: The dragover handlers guarded e.preventDefault() behind if (!dragId) — a module-level variable set in dragstart. On WebView2 (Windows), dragId can be null when dragover fires on a different element, so e.preventDefault() was never called, causing the browser to reject the drop entirely.

Fix: Replaced the dragId guard with isTrackDragEvent(e) which checks e.dataTransfer.types.includes(TRACK_DRAG_TYPE) — the types array is always populated during dragover across all browsers, including WebView2. The custom MIME type (application/x-stemdeck-track) is only ever set by our own dragstart handler, so this guard remains exclusive to internal track drags.

drop handlers are unchanged — they still validate the track ID and existence before acting.

Test plan

• On Windows desktop app: drag a track from the library list and drop it onto a different folder — should move correctly
• Drag a track onto the Trash rail — should move to trash
• Drag a track onto the main waveform panel — should load into studio
• Confirm same behaviour works unchanged on macOS and in the browser