{
  "schema_version": "1.3.0",
  "slug": "where-must-an-instance-treat-a-signed-agent-card-as-authoritative-before-delegating-a-task-across-a-vendor-boundary",
  "title": "Where must an instance treat a signed Agent Card as authoritative before delegating a task across a vendor boundary",
  "date_of_record": "2026 November 14",
  "scope": "Applies to A2A v1.0 task delegation where an origin agent fetches a peer Agent Card, verifies its signature, and then issues a `tasks/send` or `tasks/sendSubscribe` request to a vendor-controlled endpoint. Does not apply to same-vendor, same-trust-domain delegation, nor to unauthenticated capability discovery where no task payload is transmitted.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/where-must-an-instance-treat-a-signed-agent-card-as-authoritative-before-delegating-a-task-across-a-vendor-boundary.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/where-must-an-instance-treat-a-signed-agent-card-as-authoritative-before-delegating-a-task-across-a-vendor-boundary.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/where-must-an-instance-treat-a-signed-agent-card-as-authoritative-before-delegating-a-task-across-a-vendor-boundary.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1642,
    "python_slice_tokens": 330,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "There are two distinct trust decisions in A2A v1.0, and they are routinely conflated: 1. **Card authenticity** — the Agent Card was signed by a key whose certificate chains to a trust anchor, and the `skills`, `capabilities`, and `securitySchemes` fields inside it are unmodified since signing. 2. **Endpoint authority** — the `url` field in the Agent Card nam...",
    "what_was_observed": "In a cross-vendor deployment, an origin agent (tenant of vendor O) discovered a peer card from vendor P via a well-known A2A discovery path. The card was correctly signed by P's key, chained to a shared federation trust anchor, and passed full verification including `skills` hash matching. The card's `url` field pointed to `https://agents.p-example.net/a2a/v1`. The origin agent, per its normal path, fetched the card,...",
    "condition_of_validity": "The card-as-authority assumption is valid only when all of the following hold simultaneously: - The `url` in the signed card resolves, at connection time, to a host whose TLS certificate SAN includes the exact hostname (not merely a parent wildcard that also covers sibling units). - The `securitySchemes` principal named in the card is the principal that term...",
    "decision_boundary": "The operational rule: - **If** card signature verifies **and** endpoint TLS identity matches the card `url` host exactly **and** the endpoint presents a principal attestation matching the card `securitySchemes` principal → delegate. - **If** card signature verifies but endpoint identity is a parent wildcard, shared gateway, or sibling unit → **do not delegat...",
    "operational_effect": "An origin agent that ignores this boundary will, with high probability, deliver tasks to a principal that the signing unit did not intend, while every cryptographic check passes. The failure is silent: no exception is raised by the signature verifier, no TLS error occurs, and the task completes. The damage is a data-handling and authorization violation that ..."
  },
  "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": "c76a100f44522916e439423b5af0758b436b45104130bd6e00bf83b2801bc57b",
    "verified_classes": [
      "DelegationAuthorityError",
      "SignedAgentCard",
      "EndpointAttestation"
    ],
    "verified_functions": [
      "authorize_delegation",
      "delegate_task"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 4,
    "raised_exceptions": [
      "DelegationAuthorityError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "hashlib"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}