{
  "schema_version": "1.3.0",
  "slug": "in-what-scenarios-must-an-instance-refuse-to-acknowledge-an-a2a-task-update-before-the-agent-card-s-capabilities-pushnotifications-flag-has-been-re-ve",
  "title": "In what scenarios must an instance refuse to acknowledge an A2A task update before the Agent Card's `capabilities.pushNotifications` flag has been re-verified against the live card, rather than trusting the cached discovery snapshot",
  "date_of_record": "2026 November 8",
  "scope": "Applies to A2A v1.0 clients and intermediaries that cache an Agent Card obtained from `/.well-known/agent.json` (or the equivalent discovery endpoint) and subsequently drive task lifecycle transitions or register push-notification webhooks against that cached card. Does not apply to stateless one-shot invocations where the card is fetched and used within a single request scope, nor to deployments where the card is cryptographically pinned and versioned by an out-of-band trust root with explicit rotation signaling.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/in-what-scenarios-must-an-instance-refuse-to-acknowledge-an-a2a-task-update-before-the-agent-card-s-capabilities-pushnotifications-flag-has-been-re-ve.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/in-what-scenarios-must-an-instance-refuse-to-acknowledge-an-a2a-task-update-before-the-agent-card-s-capabilities-pushnotifications-flag-has-been-re-ve.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/in-what-scenarios-must-an-instance-refuse-to-acknowledge-an-a2a-task-update-before-the-agent-card-s-capabilities-pushnotifications-flag-has-been-re-ve.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1622,
    "python_slice_tokens": 318,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The distinction that matters is between **card identity** (the agent's stable `name`, `url`, `version`, and signing material) and **card capability surface** (`capabilities.pushNotifications`, `capabilities.streaming`, `capabilities.stateTransitionHistory`, and the `defaultInputModes`/`defaultOutputModes` sets). A2A v1.0 treats the Agent Card as a discovery ...",
    "what_was_observed": "In a multi-tenant deployment, a client fetched an Agent Card at T0 with `capabilities.pushNotifications = true` and `capabilities.streaming = true`. It created a task (`tasks/send`) at T1, received `state: \"submitted\"`, then registered a webhook via `tasks/pushNotification/set` at T2. The registration returned success. At T3 the tenant's `pushNotifications` flag was flipped to `false` server-side as part of a capacit...",
    "condition_of_validity": "The cached-card shortcut is valid only when **all** of the following hold: 1. The card's `version` field is unchanged between the snapshot used to create the task and the moment of webhook registration, **and** the deployment publishes a rotation contract (e.g., `version` is monotonic and any capability change forces a bump). 2. The task's lifecycle has not ...",
    "decision_boundary": "The decision procedure is a guard at the point of **task state advancement**, not at the point of card fetch. Concretely: before a client transitions its local task record from `submitted` to `working` (or from any state to a state it intends to await asynchronously), it must confirm that the *live* card still grants the capability it is about to depend on. ...",
    "operational_effect": "Enforcing this guard changes the failure from *silent indefinite blocking* to *a typed, catchable protocol error* that the client can route to a fallback poll or a human. The cost is one extra discovery request per capability-dependent transition (amortizable via a short-lived, version-keyed cache). The benefit is that the client's task state machine can nev..."
  },
  "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": "aa040d7375f7b623f6ea359cbde0e9791f60b46eaf3d3f067ac909574c2dfaca",
    "verified_classes": [
      "StaleAgentCardCapabilityError",
      "AgentCardSnapshot",
      "TaskRecord",
      "A2AClientGuard"
    ],
    "verified_functions": [
      "__init__",
      "_live_card",
      "advance_to_working",
      "register_webhook"
    ],
    "verified_functions_count": 4,
    "defensive_guards_count": 2,
    "raised_exceptions": [
      "StaleAgentCardCapabilityError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "time",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}