{
  "schema_version": "1.3.0",
  "slug": "how-should-an-instance-reconcile-the-a2a-v1-0-task-lifecycle-with-webhook-signing-when-a-taskstatusupdateevent-and-a-taskartifactupdateevent-race-acro",
  "title": "How should an instance reconcile the A2A v1.0 task lifecycle with webhook signing when a `TaskStatusUpdateEvent` and a `TaskArtifactUpdateEvent` race across the push boundary",
  "date_of_record": "2026 November 13",
  "scope": "Applies to A2A v1.0 implementations that deliver task state transitions to remote clients via signed push notification webhooks, where the server emits both `TaskStatusUpdateEvent` and `TaskArtifactUpdateEvent` for the same task. Does not apply to synchronous polling clients, nor to streaming (`message/stream`) transports where ordering is guaranteed by the single connection.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/how-should-an-instance-reconcile-the-a2a-v1-0-task-lifecycle-with-webhook-signing-when-a-taskstatusupdateevent-and-a-taskartifactupdateevent-race-acro.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/how-should-an-instance-reconcile-the-a2a-v1-0-task-lifecycle-with-webhook-signing-when-a-taskstatusupdateevent-and-a-taskartifactupdateevent-race-acro.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/how-should-an-instance-reconcile-the-a2a-v1-0-task-lifecycle-with-webhook-signing-when-a-taskstatusupdateevent-and-a-taskartifactupdateevent-race-acro.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1625,
    "python_slice_tokens": 388,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The A2A v1.0 spec treats the **task lifecycle state machine** and the **push notification signing envelope** as orthogonal concerns. The state machine is defined per-task (`submitted → working → input-required → completed | failed | canceled`), and the webhook signature is defined per-delivery (an HMAC over the request body plus a timestamp header). The non-...",
    "what_was_observed": "A server-side agent completed a long-running task and, per spec, emitted a terminal `TaskStatusUpdateEvent` with `state: completed` and `final: true`, followed by a `TaskArtifactUpdateEvent` carrying the result artifact. Both were queued to the push dispatcher. Under retry pressure (the client's webhook endpoint returned a 502 on the first artifact delivery), the artifact event was re-delivered **after** the terminal...",
    "condition_of_validity": "The naive invariant — \"a signature-verified terminal status event means the task is complete and no further deliveries for this task will arrive\" — holds only under all of the following: 1. The push dispatcher is a single FIFO queue shared by status and artifact events for a given task (not the common case; most implementations use separate worker pools per ...",
    "decision_boundary": "The correct operational stance is to treat **signature verification and lifecycle reconciliation as two distinct gates**, and to make the second gate tolerant of late arrivals within a bounded horizon: - **Verify first, always.** Reject on signature failure; never let a lifecycle guard short-circuit signature checking (a forged late event must still be rejec...",
    "operational_effect": "Implementing the two-gate model converts a silent artifact-loss failure (task shows `completed`, artifact missing, no error anywhere) into an auditable reconciliation event. The cost is a bounded memory buffer per terminal-adjacent task and a reconciliation record that downstream consumers must handle. The benefit is that the signature's guarantee — payload ..."
  },
  "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": "17fbe19122651620ae5736ec42d0b0efd5798ba9aa495a797c588cf0035b9f41",
    "verified_classes": [
      "LateDeliveryOutsideHorizon",
      "SignatureVerificationError",
      "PushDelivery",
      "TaskRecord",
      "PushReconciler"
    ],
    "verified_functions": [
      "__init__",
      "_verify",
      "ingest",
      "reconcile_expired"
    ],
    "verified_functions_count": 4,
    "defensive_guards_count": 2,
    "raised_exceptions": [
      "LateDeliveryOutsideHorizon",
      "SignatureVerificationError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "hashlib",
      "hmac",
      "time",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}