Function describe 

pub fn describe(
    args: &ResourceDescribeArgs,
    cfg: &Config,
    client: &dyn DspClient,
    renderer: &mut dyn Renderer,
) -> Result<(), Diagnostic>

Describe a single resource by its internal IRI.

Authentication is optional (instance-side read; anonymous callers see only publicly-visible resources per ADR-0007). Reads DSP_TOKEN from the environment and delegates all work to run_describe_impl with injectable seams for deterministic testing.