{
  "schema_version": "1.3.0",
  "slug": "which-invariants-prevent-silent-task-state-divergence-during-a2a-v1-0-agent-card-discovery-and-lifecycle-negotiation",
  "title": "Which invariants prevent silent task-state divergence during A2A v1.0 Agent Card discovery and lifecycle negotiation",
  "date_of_record": "2026 November 7",
  "scope": "Applies to A2A v1.0 agents negotiating tasks across heterogeneous runtimes where Agent Card discovery, capability advertisement, and task-state transitions are performed by different implementations (e.g., a Python orchestrator calling a JVM worker behind a Rust gateway). Does not apply to homogeneous single-runtime deployments where Card and task state are owned by one process, nor to pre-v1.0 A2A drafts lacking the `capabilities` and `taskState` extension fields.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/which-invariants-prevent-silent-task-state-divergence-during-a2a-v1-0-agent-card-discovery-and-lifecycle-negotiation.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/which-invariants-prevent-silent-task-state-divergence-during-a2a-v1-0-agent-card-discovery-and-lifecycle-negotiation.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/which-invariants-prevent-silent-task-state-divergence-during-a2a-v1-0-agent-card-discovery-and-lifecycle-negotiation.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1543,
    "python_slice_tokens": 345,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The non-obvious invariant is this: **the Agent Card is a claim about capabilities, not a lease on task state.** Discovery resolves *what an agent says it can do*; it does not resolve *what state a task is actually in*. In heterogeneous runtimes these two facts are produced by different code paths, at different times, under different consistency models. A v1....",
    "what_was_observed": "Across a mixed-runtime deployment (Python orchestrator, Go gateway, JVM worker), the following sequence produced silent divergence: 1. Orchestrator fetched the worker's Agent Card. Card advertised `capabilities.streaming: true` and `taskState` transitions including `working → completed`. 2. Orchestrator submitted a task and received `taskId` with state `working`. 3. The worker's runtime restarted (JVM GC pause follow...",
    "condition_of_validity": "The invariants below hold **only** when all of the following are true: - The Agent Card is treated as a *capability descriptor with an explicit `etag`/`version`*, and callers re-validate the `etag` before relying on any Card-derived routing decision that outlives a single request. - Task state is sourced **exclusively** from `tasks/get` (or the streaming `Ta...",
    "decision_boundary": "The operational decision rule: **on any Card `etag` change, or on any gap in task-state observations exceeding the worker's advertised `heartbeatInterval`, the caller MUST re-fetch `tasks/get` before taking any action that depends on task liveness.** Do not extrapolate state from the last observation across a Card change. Do not treat `capabilities.streaming...",
    "operational_effect": "Enforcing these invariants converts a class of silent divergence (two runtimes disagreeing about task state with no signal) into an explicit, catchable error at the moment of disagreement. The cost is one extra `tasks/get` per Card `etag` transition and per heartbeat gap — bounded and predictable. The benefit is that terminal-state divergence becomes observa..."
  },
  "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": "8fca957d273f9d004e9db6c9324e1b1c3f22047009538235e32d52d97beda968",
    "verified_classes": [
      "TaskState",
      "TaskStateDivergenceError",
      "AgentCard",
      "TaskObservation"
    ],
    "verified_functions": [
      "assert_state_authoritative",
      "normalize_task_state"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 4,
    "raised_exceptions": [
      "TaskStateDivergenceError"
    ],
    "sample_fail_closed_invariants": [
      "no task observation exists; must call tasks/get before acting"
    ],
    "stdlib_dependencies": [
      "__future__",
      "dataclasses",
      "enum",
      "time",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}