When platform_editor_media_drop_position experiment's isEnabled parameter is true, Dropzone accepts optional onDragOver(event) and onDropWithContext(event, traceContext) callbacks. The latter runs before upload preparation. Return false to reject the drop, or a cleanup function to release preparation state after all upload batches have been prepared.
Use onUploadsStart and its matching traceContext.traceId to associate media file IDs with the original drop. Preview callbacks can arrive later and in a different order. The existing no-argument onDrop callback and default upload behavior remain unchanged for consumers that do not opt in.