TIL that some_path.join(some_absolute_path) == some_abolute_path, which makes sense.
There exists a path_to_hg_path_buf util that you should probably use here and below.
We should see if working_directory is the same as cwd so as to not allocate in the common path. files is a performance-sensitive command in CI/server environments.
Just to make the same point as yesterday but publicly: this should only be printed if we're in no-fallback mode (and with a different error code). But we'll get to that later.