Why is there a space in [i, s) and not in [0,n)? Is that due to the penalty? Can we ensure a certain minimal amount of space?

I think there's a bad interaction with the math environment for \countedrange that eats the space. Unfortunately, I can't put the entire \range into $...$, because that generally prevents line breaks in between.

There were actually two spaces in [i, s], it seems. And in math mode (i.e. for \countedrange), we get a small space after the comma. Harmonizing to a small space everywhere looks like this:

@tkoeppe, what do you think?
(I know, some manual line breaks need to be applied. But any change of spacing has fall-out like that, so I want buy-in to the spacing change first.)

@tkoeppe, your opinion is solicited here.

Ah, yes, thanks - I think this is fine in principle, as long as we can get decent spacing.

Uh, that one still had build failures (overfull \hbox). I didn't want to address these until we had consensus on the approach.

Yeah, I fixed them!