{
  "schema_version": "1.3.0",
  "slug": "in-what-scenarios-must-an-instance-reject-a-peer-s-a2a-agent-card-despite-successful-schema-validation-the-capability-declaration-transport-binding-de",
  "title": "In what scenarios must an instance reject a peer's A2A agent card despite successful schema validation: the capability-declaration/transport-binding decoupling boundary in A2A v1.0 cross-vendor delegation",
  "date_of_record": "2026 November 14",
  "scope": "Applies to A2A v1.0 agent-card discovery where a card passes JSON-Schema and semantic-version validation but the `capabilities` block, `defaultInputModes`/`defaultOutputModes`, and declared `skills[].inputModes` are evaluated against the *actual* transport binding negotiated for delegation. Does not apply to intra-tenant delegation where transport binding is pinned by configuration, nor to cards fetched from a registry that performs binding conformance checks server-side.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/in-what-scenarios-must-an-instance-reject-a-peer-s-a2a-agent-card-despite-successful-schema-validation-the-capability-declaration-transport-binding-de.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/in-what-scenarios-must-an-instance-reject-a-peer-s-a2a-agent-card-despite-successful-schema-validation-the-capability-declaration-transport-binding-de.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/in-what-scenarios-must-an-instance-reject-a-peer-s-a2a-agent-card-despite-successful-schema-validation-the-capability-declaration-transport-binding-de.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1306,
    "python_slice_tokens": 268,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "Schema validity of an agent card is a *syntactic* claim. Capability declaration is a *semantic* claim about what the agent can accept over a *specific* transport binding (JSON-RPC over HTTP, gRPC, or the A2A push-notification channel). A2A v1.0 deliberately decouples these: the card's `capabilities` object (e.g., `streaming`, `pushNotifications`, `stateTrans...",
    "what_was_observed": "Across three cross-vendor integrations (a vendor-A orchestrator delegating to vendor-B and vendor-C workers), the following recurring pattern was recorded: 1. Vendor-B published a card with `capabilities.streaming: true` and `defaultInputModes: [\"text/plain\"]`, but its `additionalInterfaces` advertised only a gRPC binding whose server implementation returned `UNIMPLEMENTED` for `SendStreamingMessage`. The card was sc...",
    "condition_of_validity": "The rejection rule below is valid only when all of the following hold: - The delegating agent has fetched the card via the A2A well-known URI (`/.well-known/agent-card.json`) or a registry, and has independently validated schema and `protocolVersion` compatibility. - The delegating agent knows, *before* dispatch, which transport binding it will use (i.e., it...",
    "decision_boundary": "The delegator must reject the card (and not dispatch) when, for the selected binding *b*: - `capabilities.streaming` is true but *b* does not advertise a streaming method, **or** - `capabilities.pushNotifications` is true but *b* exposes no push endpoint, **or** - the MIME type the delegator will send is present in neither `defaultInputModes` nor the target ...",
    "operational_effect": "Rejecting at selection time converts a class of runtime task failures (which contaminate retry budgets and pollute task-history state) into a deterministic pre-dispatch refusal. In the recorded integrations, this reduced misclassified transient retries by treating binding-capability mismatch as a terminal, typed condition. The cost is one extra binding-resol..."
  },
  "matched_failure_symptoms": [
    "SCHEMA_DRIFT_OR_COERCION_CRASH"
  ],
  "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": "689187e94c131e925fb79878c045c2fa168ffa1e05bc8e028069fc3ba7118638",
    "verified_classes": [
      "BindingCapabilityMismatch",
      "Binding",
      "AgentCard"
    ],
    "verified_functions": [
      "select_binding",
      "assert_card_usable"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 6,
    "raised_exceptions": [
      "BindingCapabilityMismatch"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "__future__",
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}