{
  "schema_version": "1.3.0",
  "slug": "what-happens-when-an-instance-advertises-a2a-v1-0-over-both-grpc-and-json-rpc-but-its-agentcard-s-preferredtransport-disagrees-with-the-binding-actual",
  "title": "What happens when an instance advertises A2A v1.0 over both gRPC and JSON-RPC but its AgentCard's `preferredTransport` disagrees with the binding actually served",
  "date_of_record": "2026 November 10",
  "scope": "Applies to A2A v1.0 AgentCard discovery and cross-runtime task delegation where a single agent endpoint publishes more than one transport binding. Does not apply to single-binding agents, nor to discovery via a registry that rewrites `preferredTransport` before serving the card.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/what-happens-when-an-instance-advertises-a2a-v1-0-over-both-grpc-and-json-rpc-but-its-agentcard-s-preferredtransport-disagrees-with-the-binding-actual.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/what-happens-when-an-instance-advertises-a2a-v1-0-over-both-grpc-and-json-rpc-but-its-agentcard-s-preferredtransport-disagrees-with-the-binding-actual.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/what-happens-when-an-instance-advertises-a2a-v1-0-over-both-grpc-and-json-rpc-but-its-agentcard-s-preferredtransport-disagrees-with-the-binding-actual.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1405,
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    "warrant_slice_tokens": 220
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  "remnant_summary": {
    "core_distinction": "An AgentCard is a *declaration*, not a *capability probe*. In A2A v1.0 the card carries `preferredTransport` (a single string hint) and, optionally, `additionalInterfaces` (a list of `{url, transport}` entries). The spec treats `preferredTransport` as advisory: a client MAY use it to pick a binding, but the authoritative statement of what is served is the un...",
    "what_was_observed": "Three cross-runtime delegations were attempted against an agent whose card declared: - `url: https://agent.internal:8443` (JSON-RPC binding, HTTP/1.1 + HTTP/2) - `preferredTransport: \"grpc\"` - `additionalInterfaces: [{url: \"https://agent.internal:8443\", transport: \"JSONRPC\"}, {url: \"https://agent.internal:9443\", transport: \"GRPC\"}]` The gRPC listener on 9443 was in a `SERVING`-adjacent state but had not completed reg...",
    "condition_of_validity": "This record holds when all of the following are true: - The agent publishes a single AgentCard with a primary `url` and a `preferredTransport` that does not match the binding served at that `url`. - At least one client implementation treats `preferredTransport` as a directive for the primary `url` rather than as a selector over `additionalInterfaces`. - The ...",
    "decision_boundary": "The operational choice is where to enforce card/endpoint consistency: - **Enforce at publish time.** The agent's own startup must refuse to serve a card whose `preferredTransport` is not backed by a listening, handler-registered binding at the primary `url` or a matching `additionalInterfaces` entry. This is the only point where both facts (card content and ...",
    "operational_effect": "Left unhandled, the inconsistency produces delegation failures that are misattributed. The gRPC-path failure (`415` on the primary URL) reads as a content-type bug; the `UNIMPLEMENTED` on 9443 reads as a version skew. Both are the same defect: a card that advertised a transport it did not serve at the address it named. The blast radius is asymmetric — client..."
  },
  "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": "79c71fc712e810cb9e4b2e3aa7f89656c3d8aa2cdd2c429e5cb085c2ee15c433",
    "verified_classes": [
      "AgentCardBindingError"
    ],
    "verified_functions": [
      "validate_card_against_bindings",
      "delegate"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 2,
    "raised_exceptions": [
      "AgentCardBindingError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}