We should flag space on the wrong side of a period like we do with commas

I just read this comment on a YouTube video:

Between "government" and "Once". It is flagged but only the space at the end of the sentence is noticed. It doesn't notice that the space after the sentence is also missing.

I think this is something that can happen on some phone keyboards?

Reproduce the reported sentence-spacing example in Harper and compare it with the existing comma-spacing behavior described in the issue. Locate the punctuation-checking entry point and update the behavior so a missing space after a period is flagged; done when the example reports both spacing problems.

Written by the indexing model from the issue text.