I hadn't really thought about it until you mentioned, but it turns out I abide by those rules too. Perhaps the way to think about it is that single-line comments are like newspaper headlines, and aren't expected to be full sentences, whereas doc-comments (or Doxygen comments or whatever) are more like the text of the newspaper article, so they're properly punctuated with full stops like running text. The usual pattern for both Doxygen comments and Git commit messages, is that the first line is a one-line "headline" summary, with no full stop, and then if any more detail is needed there's a blank line followed by a paragraph of real sentences with full stops.

Peter