The most portable solution we've found is to send a Note with InReplyTo containing nothing but a single emoji (which might be a composite emoji) after removing whitespace. The same algorithm on the receiving side also works for Like activities with single-emoji content. We treat these as emoji reactions internally. You can add one or more of the various 'EmojiReact' platform specific cohorts if you want. Just like punycode usernames - it federates with all the things. Unlike all the other solutions we've seen...

Mike Macgirvin
🔒 Manual approvalAustralian transplant. "Machine wizard". Reverse-lefty guitarist (plays a right handed guitar upside-down and backwards). Retired decentralised communications professional that participated in early Internet/web/email/fediverse protocol standardisation and related technologies -- with stints at Stanford University, Netscape, America Online, Sun Microsystems, Symantec, University of Wollongong, and others. Music store owner, luthier, and band-instrument repair. Semiconductor and thin-film process engineer and ultra high vacuum systems specialist.
Has strong and often unpopular opinions based on real-world experience achieving communications between systems with completely different protocols and policies, as well as their underlying definitions of what "communication" actually means.
Has strong and often unpopular opinions based on real-world experience achieving communications between systems with completely different protocols and policies, as well as their underlying definitions of what "communication" actually means.
Replying to @billstatler@forum.statler.ws
My instance has rfc9421 turned on for everything by default - and I'd be happy to send some test packets and report back. However from memory nodebb isn't able to parse activities - and I don't have any way to send "posts"; so it might be a bit challenging to figure out which condition caused any failures.