If I'm understanding the thread correctly, I have a git alias to `git commit --amend --no-edit`, for exactly this workflow. When I'm hacking on something locally and want to just keep amending a commit. I only ever do this if it's HEAD though.
I go back and forth between the two approaches, but because of the whole "accidentally made some temporary changes and now it's a pain to separate/undo them because not all changes were temporary", I also usually do a jj new and then jj squash.