Function load_explicit_source_inputs_v1 

pub fn load_explicit_source_inputs_v1(
    project_root: &Path,
    source_specs: &[CliExplicitSourceSpecV1],
) -> Result<Vec<CliSourceInputV1>, CliBuildCheckErrorV1>

Reads exactly the caller-authorized source paths after containment checks. No source-root traversal or membership inference is performed.