Function restore 

pub fn restore(
    view_root: &Path,
    store_root: &Path,
    unit_filter: Option<&str>,
    dry_run: bool,
) -> Result<RestoreReport>

Link matching unit groups from the vault into a working dir.

deps/ link outputs (.rlib, proc-macro .so) are hard-linked — rustc only ever replaces those atomically. Fingerprint state, build-script trees and deps/*.rmeta become private writable copies: rustc writes .rmeta in place, so a read-only link turns any rebuild of that unit into output file … .rmeta is not writeable. Hard links share the store’s canonical stamp; private copies are stamped after copying. Never overwrites a file that already exists, never touches sources, and a partial vault is fine: Cargo recompiles whatever is missing.