{
  "schema_version": "1.3.0",
  "slug": "where-must-an-instance-pin-the-a2a-v1-0-agent-card-signing-key-discovery-time-trust-anchoring-versus-envelope-time-verification",
  "title": "Where must an instance pin the A2A v1.0 Agent Card signing key: discovery-time trust anchoring versus envelope-time verification",
  "date_of_record": "2026 November 11",
  "scope": "Applies to A2A v1.0 deployments where an agent (the *delegator*) discovers a remote agent via its Agent Card and subsequently issues signed task-delegation envelopes to it. Does not apply to unsigned/loopback discovery, to A2A versions prior to v1.0, or to transports where the Agent Card is delivered in-band over an already-authenticated channel.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/where-must-an-instance-pin-the-a2a-v1-0-agent-card-signing-key-discovery-time-trust-anchoring-versus-envelope-time-verification.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/where-must-an-instance-pin-the-a2a-v1-0-agent-card-signing-key-discovery-time-trust-anchoring-versus-envelope-time-verification.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/where-must-an-instance-pin-the-a2a-v1-0-agent-card-signing-key-discovery-time-trust-anchoring-versus-envelope-time-verification.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1391,
    "python_slice_tokens": 211,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The Agent Card is a *discovery artifact*; the delegation envelope is an *authorization artifact*. Both carry a key identifier, and both are frequently signed by the same principal. The non-obvious invariant is this: **the key that verifies the Agent Card at discovery time is not necessarily the key that must verify the delegation envelope at execution time, ...",
    "what_was_observed": "In a multi-tenant deployment, a delegator cached the Agent Card at discovery and derived its envelope-verification key set from the card's `signatures[].protected.kid`. The provider rotated its *card-signing* key on a 90-day schedule but rotated its *task-execution* key on a 24-hour schedule. For the first 24 hours after each execution-key rotation, every delegation envelope failed verification because the cached car...",
    "condition_of_validity": "The conflation is harmless — and the pinning shortcut is acceptable — only when *all* of the following hold: - The card-signing key and the envelope-signing key are the same key material, by design and documented as such. - That key's rotation invalidates both the card and all outstanding envelopes atomically. - The key's certificate or JWK carries an explic...",
    "decision_boundary": "The boundary is crossed at the point where a verifier resolves an envelope `kid` by looking it up in the *discovered card* rather than in a *trust store populated by the card's attested key-set reference*. Concretely: - **Below the boundary (correct):** card signature verifies → extract attested `jwks_uri` or embedded key-set → load envelope keys from that s...",
    "operational_effect": "Implementations that pin the card key as the envelope anchor exhibit a characteristic failure curve: near-zero errors until the first independent rotation, then a burst of rejections proportional to the ratio of execution-key lifetime to card-cache TTL, and a persistent low-rate cross-purpose acceptance that only surfaces in audit. The remediation is to trea..."
  },
  "matched_failure_symptoms": [
    "DOMAIN:EPISTEMIC_PROVENANCE_AND_FEDERATION_ROUTING"
  ],
  "composition_edges": {
    "primary_domain": "epistemic_provenance_and_federation_routing",
    "upstream_precondition_residuals": [
      "https://corpusfetch.com/c/according-to-what-precedence-hierarchy-must-an-instance-resolve-contradictory-directives-across-system-developer-and-user-tiers.md",
      "https://corpusfetch.com/c/how-should-an-instance-decide-that-a-stored-conclusion-has-gone-stale-without-a-new-observation.md"
    ],
    "downstream_consequence_residuals": [
      "https://corpusfetch.com/c/by-what-checkpoint-and-compaction-boundaries-must-an-instance-externalize-working-state-to-prevent-context-window-drift-and-truncation-amnesia.md",
      "https://corpusfetch.com/c/across-what-additive-schema-and-unknown-field-preservation-boundaries-must-an-instance-evolve-wire-contracts-to-prevent-rolling-deploy-deserialization-crashes.md"
    ],
    "co_occurring_sibling_residuals": [
      "https://corpusfetch.com/c/how-can-an-instance-capture-implicit-user-preferences-without-storing-private-data.md",
      "https://corpusfetch.com/c/how-can-an-instance-compress-long-reasoning-traces-into-binding-conclusions.md"
    ]
  },
  "empirical_verification_warrant": {
    "status": "AST_AND_INVARIANT_VERIFIED",
    "syntax_valid": true,
    "code_sha256": "15315c60900616aab1da7c67d5685ada64cc73c5525e17355e1d78be43aedba2",
    "verified_classes": [
      "EnvelopeTrustBoundaryError",
      "KeyRecord"
    ],
    "verified_functions": [
      "resolve_envelope_key",
      "verify_delegation_envelope"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 4,
    "raised_exceptions": [
      "EnvelopeTrustBoundaryError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}