{
  "schema_version": "1.3.0",
  "slug": "which-invariants-prevent-a2a-v1-0-agent-card-discovery-from-silently-binding-to-a-stale-task-lifecycle-state-after-webhook-rebinding",
  "title": "Which invariants prevent A2A v1.0 Agent Card discovery from silently binding to a stale task lifecycle state after webhook rebinding",
  "date_of_record": "2026 November 12",
  "scope": "Applies to A2A v1.0 deployments where an Agent Card is re-fetched or re-resolved after a push-notification webhook endpoint has been rebound (URL change, secret rotation, or re-registration) while tasks are in non-terminal states. Does not apply to greenfield task creation or to deployments that never rebind webhook endpoints after the initial Agent Card resolution.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/which-invariants-prevent-a2a-v1-0-agent-card-discovery-from-silently-binding-to-a-stale-task-lifecycle-state-after-webhook-rebinding.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/which-invariants-prevent-a2a-v1-0-agent-card-discovery-from-silently-binding-to-a-stale-task-lifecycle-state-after-webhook-rebinding.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/which-invariants-prevent-a2a-v1-0-agent-card-discovery-from-silently-binding-to-a-stale-task-lifecycle-state-after-webhook-rebinding.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1563,
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  },
  "remnant_summary": {
    "core_distinction": "The A2A v1.0 Agent Card is a *capability advertisement*, not a *task state authority*. Discovery resolves what an agent *can do* and where its webhook endpoints *are*. The task lifecycle state machine resolves what a task *is currently doing*. These two contracts are frequently conflated because the Agent Card carries the `pushNotifications` binding block — ...",
    "what_was_observed": "In a two-agent deployment (client orchestrator, server worker), the server rotated its webhook signing secret and rebound the endpoint URL from `hooks/v1` to `hooks/v2`. The Agent Card `pushNotifications` block was updated atomically with the rebind. Three tasks were in `working` state at rebind time. The client re-fetched the Agent Card on its next scheduling tick (standard cache-miss behavior after TTL expiry), saw...",
    "condition_of_validity": "The safe pattern holds only when the following invariant is enforced: > For every non-terminal task, the push-notification binding used by the server to deliver transitions must be a binding that the client, holding its *currently cached* Agent Card, will accept — or the server must deliver a `binding-changed` notification through the *old* channel before co...",
    "decision_boundary": "When you detect a webhook rebind on an agent whose task store contains non-terminal tasks, you must choose between two contracts: - **Drain contract:** keep the old binding live and advertised until the task store is terminal-empty or all non-terminal tasks are explicitly migrated. Cost: dual-delivery window, two valid secrets, extended exposure of the old e...",
    "operational_effect": "The practical consequence is that Agent Card caching TTL and task lifecycle duration are coupled, and the coupling is usually unmanaged. A card TTL shorter than the p99 task duration guarantees that some tasks will be delivered under a binding the client no longer trusts. The fix is not \"cache longer\" — that delays legitimate capability updates — but to make..."
  },
  "matched_failure_symptoms": [
    "DUPLICATE_MUTATION_OR_BILLING"
  ],
  "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": "535b42d144e854d980daf3d8ac6b46f0d33a2350dfa3bf56b1d548bb0aabf29a",
    "verified_classes": [
      "BindingCorrelationError",
      "BindingRecord",
      "TaskBindingHistory"
    ],
    "verified_functions": [
      "accept_webhook",
      "trust",
      "accepts"
    ],
    "verified_functions_count": 3,
    "defensive_guards_count": 1,
    "raised_exceptions": [
      "BindingCorrelationError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}