v0.4.0

Security

• A delegate with no enclave could be recorded as caller_attestation="hardware"
  by relaying an honest hardware peer's attestation: it asked that peer's public
  /.well-known/ca2a/channel endpoint to attest under the target's challenge and
  presented the result as its caller_offer. Caller offers are now minted in a
  separate role, signed under their own binding prefixes (ca2a-*-caller-v2|),
  and the handshake endpoint only mints callee-role offers. The caller must also
  send caller_possession, a MAC over the request transcript keyed from X25519
  between its attested channel key and the callee's, which the callee verifies
  before recording any outcome.

Changed

• Breaking for callers that send caller_offer (ca2a-caller-offer-v2). A
  pre-v2 caller offer has no role and no caller_possession and is refused with
  ATTESTATION_FAILED. Callers that send no offer, and the handshake response,
  are unchanged on the wire. BaseProvider.attest and the binding helpers
  (tpm_qualifying_data, snp_report_data, tdx_report_data) take a keyword
  role, defaulting to the callee role; a custom Verifier must derive the
  binding under report.role.