ESC [ 3 K: Erase Line Right Unless Pending Wrap
Found at https://terminalguide.netlify.com/seq/, urxvt supports this sequence.
As far as I recall, this is exactly what we do on
ESC [ K (740789).
We could make
ESC [ 3 K an alias for this (to encourage apps emitting this one, and eventually perhaps revert
ESC [ K to the official braindamaged behavior).