Function plan 

pub fn plan(
    program: PathBuf,
    layout: &Layout,
    create: &[String],
    extra: &[String],
) -> Result<Invocation, String>

Builds the daemon invocation for a layout.

extra is passed through verbatim after the derived flags, so any daemon flag this does not know about is still reachable without this function having to grow a copy of the daemon’s argument parser — which would be a second parser to keep in step, and the kind that fails by silently dropping a flag rather than by refusing it.

Errors

Refuses when the credential or the trusted-key file is missing, naming the command that writes them. Starting without them would produce a node that either accepts everyone or answers 503 to every read, and both look like a broken install rather than an unfinished one.