thirdshift update #34

Parent

#30

What to build

thirdshift update replaces the installed binary with the latest stable GitHub Release, using dist's axoupdater library with the install receipt written by the shell installer.

• When it updates, or is already on the latest version, it says so on stderr and exits 0.
• On failure (no network, GitHub unavailable) it explains on stderr and exits 1.
• With no install receipt (built from source, installed from crates.io, or copied by hand) it refuses, says why, names the command that updates that kind of install, and exits 1.
• stdout always stays empty.
• Replacing the binary must be safe while a Run is using the old binary.
• A Run never checks for updates or updates itself.

HTTPS must go through rustls, never OpenSSL, so the musl binary stays statically linked. The release pipeline's build and Rocky/WSL smoke jobs must still pass on this PR.

Acceptance criteria

• thirdshift update updates to, or confirms, the latest stable release. Messages go to stderr, stdout stays empty, and it exits 0.
• With HOME and the XDG config location pointing at an empty temporary directory, it exits 1 with a reinstall hint on stderr and empty stdout. This is covered by an offline integration test on the binary-subprocess seam.
• Network or GitHub failures exit 1 with an explanation on stderr.
• No OpenSSL in the dependency tree, and the musl build and smoke jobs still pass.
• Runs never invoke the updater.
• The README's Updating section says thirdshift update.

Blocked by

• Command surface: help, version and argument errors #31 (command dispatch)
• Release pipeline: binaries, installer and platform smoke tests #33 (installer receipt and install path)