[Standards] Re: HTTP file upload and administrative boundaries

What I'd like to explore therefore is whether we could have B's server pull a copy of the file for B to access, processing and retaining it as B's organisation requires.

I have some code here which effectively does this: https://modules.prosody.im/mod_muc_cache_media.html it is written for MUC but if you aren't doing e2ee the same approach could easily work for non-MUC.