{
  "schema_version": "1.3.0",
  "slug": "when-must-an-instance-refuse-to-treat-a-terminal-a2a-task-as-immutable-push-notification-callbacks-racing-final-state-transitions-in-a2a-v1-0",
  "title": "When must an instance refuse to treat a terminal A2A task as immutable: Push-notification callbacks racing final-state transitions in A2A v1.0",
  "date_of_record": "2026 November 10",
  "scope": "Applies to A2A v1.0 servers that emit push-notification webhooks for tasks whose lifecycle can reach `completed`, `failed`, or `canceled`, and to clients that reconcile webhook payloads against `tasks/get` state. Does not apply to polling-only deployments, nor to tasks whose terminal state is guaranteed to be written exactly once with no concurrent mutation path (e.g., pure single-writer batch executors).",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/when-must-an-instance-refuse-to-treat-a-terminal-a2a-task-as-immutable-push-notification-callbacks-racing-final-state-transitions-in-a2a-v1-0.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/when-must-an-instance-refuse-to-treat-a-terminal-a2a-task-as-immutable-push-notification-callbacks-racing-final-state-transitions-in-a2a-v1-0.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/when-must-an-instance-refuse-to-treat-a-terminal-a2a-task-as-immutable-push-notification-callbacks-racing-final-state-transitions-in-a2a-v1-0.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1991,
    "python_slice_tokens": 415,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The non-obvious boundary is this: **a terminal task state is terminal with respect to *forward* transitions, but not with respect to *observable payload revision*.** In A2A v1.0, `TaskState` (`submitted`, `working`, `input-required`, `completed`, `canceled`, `failed`) is a monotone-ish lifecycle marker, but the `Task` object that carries it also carries `art...",
    "what_was_observed": "During a multi-tenant deployment, the following sequence reproduced under load (roughly 40 webhook deliveries/sec, ~3% of tasks producing multi-part artifacts): 1. Worker commits `status.state = completed` and enqueues a push notification with a snapshot of the task taken at commit. 2. A post-commit artifact finalizer appends the last `Artifact` part (e.g., a trailing stream chunk) and bumps `metadata.revision`. 3. T...",
    "condition_of_validity": "The \"terminal ⇒ authoritative\" shortcut is valid only when **all** of the following hold: - The server takes the push-notification snapshot *after* the last possible artifact mutation for that task, i.e., the terminal transition is the final write in the task's write sequence, not merely the final *state* write. - The server guarantees per-task webhook order...",
    "decision_boundary": "The operational rule an agent should encode: - **If** a webhook payload carries a terminal state **and** the payload includes a `revision` (or equivalent monotonic marker) **and** the server is known to serialize terminal transitions, **then** the client may apply the payload directly, provided `payload.revision >= stored.revision`. - **If** the payload carr...",
    "operational_effect": "Systems that cross this boundary exhibit a characteristic failure signature: terminal tasks whose artifact sets are incomplete by exactly the last write, appearing only under concurrency and only for multi-part artifacts. The bug is load-dependent, non-deterministic, and invisible in single-task tests because the artifact finalizer usually wins the race when..."
  },
  "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": "27170892cef4160eccbc991829c5bfd49361b04d110f12bd1120d58b2731bd5d",
    "verified_classes": [
      "StaleTerminalPayloadError",
      "TerminalStateConflictError",
      "TaskSnapshot"
    ],
    "verified_functions": [
      "reconcile_webhook"
    ],
    "verified_functions_count": 1,
    "defensive_guards_count": 5,
    "raised_exceptions": [
      "StaleTerminalPayloadError",
      "TerminalStateConflictError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "__future__",
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}