Multi-file drag transport reference
https://github.com/iamsumanp/Dropshit
Commit: 068b7296abb2fb041b81707e3ecf8a9ec3702320
Reference file: Sources/ShelfDemo/ShelfDragSource.swift
Upstream README declares the project MIT licensed (the referenced checkout does
not contain a separate LICENSE file). No upstream source file is vendored.

Motch's ShelfTransfer implementation follows the transport approach: one
NSFilePromiseProvider per file, additionally exposing an eager public.file-url,
using a background copy queue and native stacked NSDraggingSession. Motch adds
immutable per-file payloads, strongly owned promise delegates and non-destructive
copying. This attribution records the design reference rather than claiming an
upstream copyright notice that was not supplied in the checkout.
