The freshen tests built a fixture and never ran freshen. They now run
gen and freshen through the command entry point on a temp dir: an
unchanged tree leaves the manifest's entries as they were, and a
modified file (also one edited without changing its size), a new or a
deleted file gives a manifest that lists exactly the tree, with sizes,
hashes and mtimes from disk, on which check passes.
New fetch tests run the command against an httptest server: a nested
tree lands complete, a hash mismatch exits non-zero and leaves no file,
and a partly filled destination gets every listed file downloaded again
and replaced, while a file the manifest does not list is left alone.
Model: opus-5-5
sneak