Result delivery

Mode	Trigger	Who verifies the result
Sync-HMAC (agentic)	Verification request created with no callbackUrl	The RS, after the wallet relays the signed result + HMAC
Async callback (legacy)	callbackUrl provided	The callback receiver

The wallet never holds the callbackSecret; it only relays the signed artifact. Integrity rests entirely on the HMAC, and the RS must reject a missing/invalid signature or a stale timestamp.