Function install_all 

pub fn install_all(
    git: &dyn GitRunner,
    fetcher: &dyn Fetcher,
    builder: &dyn ComponentBuilder,
    specs: &[RequiredSpec],
    cache_root: &Path,
    user_root: &Path,
    policy: RefreshPolicy,
) -> Vec<Install>

Run every required spec, in declaration order.

One spec’s failure never stops the next: a user with five plugins and one broken source should lose that one, not the four that work.