Function fast_with 

pub fn fast_with(
    root: &Path,
    share: Option<&Path>,
    held: Option<&CapabilityRegistry>,
) -> CommandGraph

The same, for a caller that already holds a registry.

A server does. Building a second one to answer one page costs what building the first one cost and describes exactly the same executable: /cockpit/commands did that on every request whose cache was cold, which the no-rebuild sweep now refuses. None is for a caller with no registry of its own, which then pays for one.

use majordomus_cli::command_graph::load;
let root = std::env::temp_dir().join(format!("mj-fast-with-{}", std::process::id()));
std::fs::create_dir_all(&root).unwrap();
// a cold cache is built from the registry the caller holds
let held = load::registry();
let graph = load::fast_with(&root, None, held.as_ref());
// a warm cache is the answer, whichever registry is or is not held
load::write_cache(&root, &graph).unwrap();
assert_eq!(load::fast_with(&root, None, None), graph);
std::fs::remove_dir_all(&root).unwrap();