This feels like it's headed in the wrong direction -- I imagine we'll be better off in the long run normalizing paths at the last possible second.

Fixing this properly is probably entangled with a lot of other stuff, but I'll accept a change to isRelevantMessage() instead which accounts for this normalization and treats \x\y as matching /x/y or whatever, if that's reasonable? That is, just make \x\y a "relevant message" if /x/y was changed.

In the long run, when running on Windows I think we should try to keep paths in Windows format and, e.g., show the user Windows paths, since this is likely what they expect and are most familiar with. Things maybe become more ambiguous in some contexts (e.g., there may be some value in normalizing paths headed to the server, so that changes look identical whether they came from a Windows machine or not).

Is doing this correction in isRelevantMessage() instead reasonable?

That seems reasonable. I'll push an updated diff later today, which tries both forms of slashes in isRelemvantMessage() if running on Windows.