This is a matter of encoding. It's got nothing to do with typography. Typesetting software should do the right thing. There aren't any rules for spacing apart f

This is a matter of encoding. It's got nothing to do with typography. Typesetting software should do the right thing. There aren't any rules for spacing apart from what the font designer specified. Of course, the software has to understand what it is that it is typesetting, and the font needs to define spacing in such a way that the typesetting software can do things as intended, so the specification for authors here is really defined by the software. If it wants two spaces after a period, then give it two. If it wants one, then give it one. I suspect that most software expects one. In a fully pedantic world, we'd have different unicode code points for "gap between word", "gap after sentence", and presumably others to cover every situation, and the font designer would then have full control.