[CalvinAllen]

Problem

dtvem install makes the first installed version of a runtime the global version, and dtvem uninstall refused to remove the global version until a different one was set. With only one version installed there is nothing to switch to, so the last version of a runtime could never be uninstalled.

Changes

• Uninstalling the global version
  • When it is the only installed version, uninstall now proceeds. It warns before the confirmation prompt, then removes the runtime's entry from the global runtimes.json once the files are deleted. Other runtimes' entries are kept. Canceling at the prompt leaves everything as it was.
  • When other versions are installed, it is still refused, and the error now lists the other installed versions.
• New config.UnsetGlobalVersion removes one runtime's entry from the global config. It does nothing when the file or the entry is missing, and it returns an error instead of rewriting a config it cannot parse.
• Local-version warning fix. Uninstall's "active local version" warning used provider.LocalVersion(), which falls back to the global version. So it fired for every global version and named the obsolete dtvem.config.json. Uninstall never reached that warning for the global version before, so this change would have exposed it. The warning now uses config.Resolve, appears only when a project file (.dtvem/runtimes.json, .tool-versions, .ruby-version, …) pins the version, and names that file.

Testing

• ./rnr check passes (format, lint with 0 issues, all tests).
• New unit tests:
  • UnsetGlobalVersion: removes only the target runtime, leaves valid JSON when the last entry is removed, handles a missing file and a missing entry, and does not rewrite a corrupt config.
  • otherVersions and localPinSource: a global version alone is not a local pin, a project .ruby-version with a partial version is a pin, and a pin of a different version is ignored.
• Manual run of a built binary against a temporary DTVEM_ROOT:
  • The global version is refused while another version is installed.
  • With one version left, uninstall removes it and clears only that runtime's global entry.
  • The local warning appears only inside a directory with .ruby-version, and it names that file.