The prefix, e.g. "fixup! " can be configured with the low-level property log.useCommitMessage.prefix.

Please take a look at https://www.syntevo.com/blog/?p=4751.

For what language?

One further clarification: what should happen if you paste some text containing tab characters?

For me it often happens that I need to amend different commits in a row. I now use "Use Message for Commit" and commit my changes (for multiple commits). If I have done all my commits, I use Interactive Rebase with one of the Auto-Squash options. I can't imagine a simpler work-flow. One always need to select the files to commit, select the commit's message to use.

Adding this to the Commit would make the already difficult Commit even more difficult to catch all border cases. So, for example, it is unexpected to get a conflict when committing, but this might happen with your suggestion 2 times - for the necessary rebase after the commit and for the auto-stash/apply/stash if there are local changes.

The File Log or Subdir Log windows do not allow to commit, so this command would be useless there.

Did you see the 3 options of the "Auto-Squash"-button in the Interactive Rebase dialog?

But it would be tricky, because there could be other obsolete worktrees, too, that silently could be deleted, too.

Please try version 19.1.

I've scheduled it for the Journal for v19.2. What exactly do you mean with "Log for" Graph window?