Function execute 

pub async fn execute(
    call: &CapabilityCall,
    runtime: &PlanRuntime,
    self_provider_id: &str,
    atlas: &mut AtlasClient,
    plan_id: &str,
) -> CapabilityCallResult

One in-process builtin (no network, runs in executor’s own process). call.contract_id’s last segment names the operation — e.g. robonix/system/executor/builtin/read_file → read_file.