The Chicago Manual indeed advises against spaces, but it’s written for books. AP Stylebook — that recommends spaces — is for papers. Comments are an even shorter form, so they’re closer to AP than to Chicago.

When I go to print, I use hairspace, but it’s not worth the trouble in comments.

> Comments are an even shorter form, so they’re closer to AP than to Chicago.

I’m not sure I agree with using length as the metric to decide which style guide is more appropriate for comments. I’d rather follow one consistent style in general than change it depending on the type of content I’m writing.

Still, good point on the style guides targeting specific usages.