feat(sdk): add Python SDK — port TypeScript verify.ts to Python (#15)

[nanookclaw]

Summary

Implements Issue #15: Python port of the TypeScript SDK for native attestation verification in Python-based Working Group members (APS, AgentID, Agora all use PyCA per the WG thread).

What this adds

sdk/python/
  src/open_agent_trust/
    __init__.py   # public API
    types.py      # dataclass mirrors of TS types
    verify.py     # 14-step verification protocol
  tests/
    test_verify.py  # 20 tests — all passing
  pyproject.toml    # pip install open-agent-trust
  README.md

Usage

from open_agent_trust import verify_attestation, RegistryManifest, RevocationList

manifest = RegistryManifest.from_dict(manifest_json)
revocations = RevocationList.from_dict(revocations_json)

result = verify_attestation(token, manifest, revocations, expected_audience="https://your-api.com")
if result.valid:
    print(result.claims.scope)   # ['read']
    print(result.issuer.issuer_id)

Implementation

• Ed25519 signature verification via cryptography (PyCA) — matches WG member tooling
• JWT decode via PyJWT with EdDSA algorithm support
• All 14 steps from spec/03-verification.md implemented with matching comment references
• Grace period: 90-day deprecated key window (spec/04-key-rotation.md)
• Fast-path revocation list check before manifest lookup

Tests (20/20 passing)

Covers all acceptance criteria from Issue #15:

Test	Scenario
✅ valid attestation	Happy path + claims extraction
✅ valid with nonce	Per-session replay prevention
✅ unknown issuer	Step 4
✅ revoked issuer (manifest)	Step 5
✅ suspended issuer	Step 5
✅ unknown key	Step 7
✅ revoked key (manifest status)	Step 8
✅ revoked key (fast-path list)	Pre-manifest fast reject
✅ invalid signature	Wrong keypair
✅ tampered token	Payload mutation
✅ malformed JWS	Garbage input
✅ expired attestation (JWT exp)	Step 13
✅ expired registry key (expires_at)	Step 10
✅ deprecated key past grace period	Step 9b
✅ deprecated key within grace period	Step 9c — ACCEPT
✅ audience mismatch	Step 13
✅ nonce mismatch	Step 13
✅ nonce not required	Token has nonce, service doesn't check
✅ claims populated on success	sub/aud/scope/constraints/user_pseudonym
✅ from_dict() round-trip	RegistryManifest.from_dict()

Dependencies

• Python ≥ 3.10
• cryptography >= 41
• PyJWT >= 2.8