postMessage() should throw if any duplicate transferable is found in transferList: - https://html.spec.whatwg.org/multipage/structured-data.html#structuredserializewithtransfer (Step 2.3)
Created attachment 434575 [details] Patch
Created attachment 434587 [details] Patch
Committed r280476 (240111@main): <https://commits.webkit.org/240111@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 434587 [details].
<rdar://problem/81327518>