Problem #
Authentication, repository identity, SSH identity, shadow installations, stale builds, and lexicon drift currently require manual diagnosis; --version does not identify the running build.
Acceptance criteria #
- Add
tang doctorwith machine-readable checks and actionable failures. - Check auth/session metadata, current repo, remotes, executable path, PATH shadows, runtime, and service reachability.
- Embed build commit/time when available and expose source/build provenance.
- Report lexicon/build drift without modifying user state.