[drk-ram]

What

Hardens cryptographic key parsing, RFC 8785 canonicalization, JSON file loading, and revocation snapshot freshness enforcement across ca2a_verify and ca2a_runtime:

1. Rejects RFC 7517 / RFC 7518 / RFC 8037 private or symmetric JWK members (d, p, q, dp, dq, qi, oth, k) and enforces canonical unpadded 32-byte base64url public keys in src/ca2a_verify/dag.py and src/ca2a_runtime/agent_manifest.py.
2. Rejects lone UTF-16 surrogates (U+D800..U+DFFF) in src/ca2a_runtime/canonical.py string values and object keys with a deterministic ValueError instead of leaking UnicodeEncodeError.
3. Rejects duplicate JSON object keys via object_pairs_hook in src/ca2a_verify/verify.py when loading delegation chain and revocation files.
4. Raises RevocationStatusUnknown in src/ca2a_runtime/delegation/credential.py when max_revocation_staleness is set and RevocationSnapshot.as_of > now.

Why

Closes #267.

Security impact

Touches src/ca2a_verify/ and src/ca2a_runtime/delegation/:

• Prevents private or symmetric JWK key material from being accepted in public verification JWKs or Agent Manifest trust anchors, and blocks non-canonical base64url key representations (padding, standard base64 alphabet characters, non-zero trailing bits, or non-32-byte Ed25519 keys).
• Enforces RFC 8785 I-JSON lone-surrogate rejection with a deterministic ValueError during canonical signing/verification.
• Prevents JSON key-shadowing ambiguities in offline chain and revocation verification files.
• Prevents a future-dated RevocationSnapshot.as_of from producing a negative now - revocations.as_of delta that bypasses max_revocation_staleness indefinitely.

Test plan

• pytest passes (pytest tests/ -q — 875 passed, 16 skipped)
• ruff check passes (ruff check src/ tests/ — All checks passed!)
• mypy passes (mypy src/ca2a_runtime/ src/ca2a_verify/ — Success: no issues found in 47 source files)
• Manual test performed (describe steps below if applicable)

Verified counterfactual failures for all four fixes when each guard is disabled, and ran bandit -r src/ -c pyproject.toml with zero issues.

DCO sign-off

• I certify that I wrote or have the right to submit this contribution, and I agree to the
  Developer Certificate of Origin (https://developercertificate.org).

[github-actions]

Thanks for this, @drk-ram. Closing it for now, and it is not about the change itself.

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[github-actions]

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