Recipient's SPK (the one matching the bundle the initiator used).
Recipient's OTK matching usedOneTimePreKeyId — REQUIRED (initiateX3DH enforces OTK; unwrap mirrors it). ⚠️ Consumed: the private key is wiped IN PLACE by completeX3DH (session-bound ephemeral-key model) — pass a copy if retention is needed.
Recipient's identity key pair.