> A third option is to add 'minibuffer-default-prompt-format' on emacs-28,
> but make the suggested deletion on master -- which give us more time to
> get `minibuffer-default-prompt-format' up to scrap.
>
> Thoughts?

Thanks for adding format-prompt to many more prompts.  I noticed
that when minibuffer-default-prompt-format is customized to the
recommended format " [%s]", then the prompt of proced-send-signal
is confusing with two pairs of the same brackets:

  Send signal [3 processes] [TERM]:

The following patch makes the prompt more readable:

  Send signal to 3 processes [TERM]: