{
  "schema_version": "1.3.0",
  "slug": "in-what-scenarios-must-an-instance-reject-a-peer-agent-card-that-verifies-cryptographically-but-violates-cross-vendor-capability-invariants",
  "title": "In what scenarios must an instance reject a peer Agent Card that verifies cryptographically but violates cross-vendor capability invariants",
  "date_of_record": "2026 November 14",
  "scope": "Applies to A2A v1.0 peers that discover remote Agent Cards over signed JSON-RPC and delegate tasks across vendor boundaries. Does not apply to same-vendor intra-cluster delegation where capability contracts are enforced by a shared schema registry, nor to unsigned localhost discovery during development.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/in-what-scenarios-must-an-instance-reject-a-peer-agent-card-that-verifies-cryptographically-but-violates-cross-vendor-capability-invariants.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/in-what-scenarios-must-an-instance-reject-a-peer-agent-card-that-verifies-cryptographically-but-violates-cross-vendor-capability-invariants.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/in-what-scenarios-must-an-instance-reject-a-peer-agent-card-that-verifies-cryptographically-but-violates-cross-vendor-capability-invariants.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1590,
    "python_slice_tokens": 310,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "A signature proves *who* authored an Agent Card. It does not prove that the card *describes a task surface the receiving runtime can honor*. The boundary that bites operators is this: **a cryptographically valid Agent Card can still be operationally invalid** because the invariant that matters at delegation time is not authenticity but *capability composabil...",
    "what_was_observed": "During cross-vendor delegation between a vendor-A orchestrator and a vendor-B worker, the following sequence reproduced reliably: 1. Vendor B published a signed Agent Card declaring `defaultInputModes: [\"application/json\"]` and a skill `invoice.extract` with `inputModes: [\"application/pdf\"]`. 2. The signature verified against vendor B's published JWKS. `kid` matched, `alg` was `ES256`, the canonicalized payload hashe...",
    "condition_of_validity": "The invariant holds—i.e., you *must* apply capability-invariant checks rather than trusting the signature—under all of the following: - The peer is a **different vendor** or a different trust domain than the caller (cross-boundary). - The local orchestrator makes **pre-flight decisions** (routing, retry, fallback) based on card-declared fields rather than on...",
    "decision_boundary": "The decision boundary is between **rejecting at discovery** and **rejecting at delegation**: - **Reject at discovery** (do not add the peer to the routing table) when the card is *internally inconsistent*: a skill's `inputModes` contains a MIME type absent from `defaultInputModes` **and** the card declares `enforceInputModes: true`; or `securitySchemes` refe...",
    "operational_effect": "Applying the invariant changes three things: 1. **Pre-flight cost.** Card parsing now includes a capability-resolution pass (resolve skill-level `inputModes` against `defaultInputModes`, resolve `securitySchemes` against `security`). This is O(skills × modes) per discovery, cached per card `version`/`etag`. 2. **Failure taxonomy.** Post-acceptance opaque err..."
  },
  "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": "681476763da6f0fd554f02012d4a8c14bf72fafe2da7b64e4f1277a772f2f4ad",
    "verified_classes": [
      "CapabilityInvariantError",
      "AgentCard",
      "Delegation"
    ],
    "verified_functions": [
      "resolve_input_modes",
      "assert_delegable"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 5,
    "raised_exceptions": [
      "CapabilityInvariantError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "__future__",
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}