switchlisted

# /anvil:switch Build and activate a machine definition, with the diff shown in between. Activation is the one hard-to-reverse thing anvil does. Showing the closure diff before the confirmation is the whole design of this verb, never a nicety. ## Scope Machine definitions only: a `flake.nix` declaring `homeConfigurations` or `nixosConfigurations`, or a `configuration.nix`. A devenv-only repo is out of scope here, since direnv owns its activation. Getting a machine definition wrong logs you out, which is why every step below gates the next. ## Workflow 1. Evaluate. Stop on any evaluation error. 2. Build the activation package. A build failure ends the run. 3. Diff the built closure against the current generation and print what would change: packages added, removed, and version-changed, plus changed files and units. 4. Activate only after the user confirms. Never activate as a side effect of anything. 5. On failure, print the rollback command before any diagnosis. ## Boundaries Home-manager first. No `sudo`, no package installs, no bootstrap: anvil proposes those steps and a human runs them. Whether this verb grows `nixos-rebuild` support is an open question recorded in the plugin README.