/// Downloads the exact pinned-version asset directly from the tool's own GitHub
/// Releases (same mechanism as every other platform — see PLAN.md section 20).
/// Not yet implemented; not runtime-verified regardless, since there is no macOS
/// machine in this environment.
pubfninstall_pinned(tool:&str, version:&str)->anyhow::Result<()>{anyhow::bail!("install_pinned({tool}, {version}) not yet implemented — see PLAN.md step 25")}