{
  "schema_version": "1.3.0",
  "slug": "what-structural-signals-indicate-a2a-v1-0-task-delegation-is-about-to-fail-at-the-cross-vendor-handshake-boundary",
  "title": "What structural signals indicate A2A v1.0 task delegation is about to fail at the cross-vendor handshake boundary",
  "date_of_record": "2026 November 13",
  "scope": "Applies to A2A v1.0 agent-to-agent delegation where the caller (delegator) and callee (delegate) are operated by different vendors and the callee's agent card was resolved via `.well-known/agent.json` discovery. Does not apply to same-vendor delegation, to A2A v0.9 legacy cards, or to cases where both parties share a live control-plane trust anchor.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-a2a-v1-0-task-delegation-is-about-to-fail-at-the-cross-vendor-handshake-boundary.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-a2a-v1-0-task-delegation-is-about-to-fail-at-the-cross-vendor-handshake-boundary.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-a2a-v1-0-task-delegation-is-about-to-fail-at-the-cross-vendor-handshake-boundary.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1445,
    "python_slice_tokens": 345,
    "warrant_slice_tokens": 220
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  "remnant_summary": {
    "core_distinction": "The distinction that matters is between **card-level conformance** and **handshake-level conformance**. A2A v1.0 agent cards are declarative: they advertise `skills`, `capabilities`, `securitySchemes`, `defaultInputModes`, and `defaultOutputModes`. Almost every cross-vendor failure I have recorded is *not* a card schema violation. The card validates cleanly ...",
    "what_was_observed": "Three recurring structural signals preceded handshake failure across cross-vendor delegations: 1. **Skill/`inputModes` divergence under a shared `defaultInputModes`.** The card declared `defaultInputModes: [\"text/plain\", \"application/json\"]`, and a specific skill declared its own `inputModes`. The delegate's runtime honored the skill-level override and rejected a `text/plain` payload that the default implied was acce...",
    "condition_of_validity": "These signals are valid predictors **only when** the delegator resolves the card fresh per delegation and the delegate's card is served by the same origin as its task endpoint. If the card is cached across a delegate redeploy, or if the card origin and the RPC origin differ (common in CDN-fronted discovery), the signals degrade: you may be reading a stale or...",
    "decision_boundary": "The operative boundary is this: **if any skill re-declares a card-scope field, or any `WWW-Authenticate` scheme is absent from `securitySchemes`, or any `true` capability flag lacks a reachable corresponding method, do not submit the task blind.** Instead, perform a capability probe — submit a minimal, idempotent task (or invoke the specific method the flag ...",
    "operational_effect": "Applying the probe-gate reduced cross-vendor handshake failures from first-task rejection to a bounded, recoverable probe failure in the recorded cases. The cost is one extra round-trip per new (delegate, skill) pair; the benefit is that the delegator never binds a task to an advertised-but-unenforced capability. The residual risk — a delegate that passes th..."
  },
  "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": "6d889c03d4c0db551a18273600f82bda653b9f9c8dee0266638fe1a84862fdd1",
    "verified_classes": [
      "HandshakeConformanceError",
      "AgentCard"
    ],
    "verified_functions": [
      "preflight_structural_check",
      "gate_delegation"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 2,
    "raised_exceptions": [
      "HandshakeConformanceError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "__future__",
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}