What happens here is that when stopping on an "edit" todo entry, we rely on the
assumption that if the .git/rebase-merge/amend file exists, the command was
successful, and if it doesn't, there was a conflict. The problem is that when
you stop on an edit command, and then run a multi-commit cherry-pick or rebase,
this will delete the amend file. You may or may not consider this a bug in git;
to work around it, we also check the existence of the rebase-merge/message file,
which will be deleted as well by the cherry-pick or revert.
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