Constant FN_ID_NUB_PUT_CAP 

pub const FN_ID_NUB_PUT_CAP: u32 = 4;

fn_id for the heap-resident cap directory put_cap RPC.

Payload: rkyv-archived javm_cap::wire::WireCap. Guest decodes into a Cap, computes its content hash, inserts the cap into the guest-resident DIRECTORY (a Mutex<HashMap<CapHash, Box<Cap>>> living in talc heap), and replies with the rkyv-archived CapHash (raw 32 bytes).