Mark cross-wiki uploads with a change tag, but properly. Right now it's a hack in WikimediaEvents, where it really doesn't belong.
I've thought about this a bit more.
We're actually using the 'cross-wiki-upload' tag to mean two things:
- Upload completed using the upload dialog
- Upload that was actually cross-wiki
We can mostly get away with it in Wikimedia environment, since there's no way to use upload dialog to upload to local wiki now (except for using it at Commons), and there's no way of cross-wiki uploading other than the upload dialog. But both of these may change in the future. Non-Wikimedia users are more likely to use the upload dialog without cross-wiki uploading, though.
So I think we should continue having the implementation of 'cross-wiki-upload' tag, which is fairly Wikimedia-specific, in the WikimediaEvents[rEWMV] extension (or we could move it to operations/mediawiki-config[rOMWC] if we fancy). But we could clean it up a bit after some recent fixes to upload tagging (T122089).
And we could tag upload dialog uploads separately if we want to, but I don't think we need it now.