Constant RECEIPT_DOMAIN_TAG_V2 

pub const RECEIPT_DOMAIN_TAG_V2: &[u8] = b"agentvisor-receipt-v2\0";

Domain-separation tag prepended to every version-2 receipt signing message. The trailing NUL makes the tag self-delimiting so no JCS body could extend it into a different tag.

Wire format: every v2 receipt ever issued is signed over these bytes. They predate the ProofVisor name and must never be renamed.