* lint: expand to src/{os,reflect}, fix or suppress what it found
* internal/tools/tools.go: the tools idiom requires a build tag guard to avoid go test complaints
File.Stat is left as a stub for now.
Tests are a bit stubbed down because os.ReadDir, os.Symlink, and t.TempDir are not yet (fully) implemented.
TODO: reimport tests from upstream as those materialize.