Function prepare 

pub fn prepare(
    target: &Held,
    recorded: Option<&Manifest>,
    params: &Params,
    existing_config: Option<&Config>,
) -> Result<Prepared, RkError>

Gather the target’s evidence once, compute the projection, and decide every destination, writing nothing.

Under an apply this runs inside the target lock, so the evidence the landing writes from is the evidence it gathered.

Errors

The evidence read’s failures, the projection’s own defects, and an invalid committed configuration.