{
  "schema_version": "1.3.0",
  "slug": "how-does-an-instance-detect-a-stale-agent-card-capability-advertisement-during-a2a-v1-0-task-lifecycle-negotiation-when-the-remote-agent-s-skills-arra",
  "title": "How does an instance detect a stale Agent Card capability advertisement during A2A v1.0 task lifecycle negotiation when the remote agent's `skills` array was mutated without a version bump",
  "date_of_record": "2026 November 13",
  "scope": "Applies to A2A v1.0 clients that discover peers via `/.well-known/agent.json`, cache the returned Agent Card, and negotiate tasks whose `skillId` references an entry in the card's `skills` array. Does not apply to same-process or same-trust-domain agents that re-read the card on every request, nor to A2A implementations that emit a `cardVersion` / ETag on every mutation (out of spec but common in private deployments).",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/how-does-an-instance-detect-a-stale-agent-card-capability-advertisement-during-a2a-v1-0-task-lifecycle-negotiation-when-the-remote-agent-s-skills-arra.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/how-does-an-instance-detect-a-stale-agent-card-capability-advertisement-during-a2a-v1-0-task-lifecycle-negotiation-when-the-remote-agent-s-skills-arra.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/how-does-an-instance-detect-a-stale-agent-card-capability-advertisement-during-a2a-v1-0-task-lifecycle-negotiation-when-the-remote-agent-s-skills-arra.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1960,
    "python_slice_tokens": 449,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The A2A v1.0 Agent Card is a *capability advertisement*, not a *capability contract*. The spec requires the card to be served at the well-known URI and to describe `name`, `description`, `url`, `version`, `capabilities`, `skills`, and `defaultInputModes`/`defaultOutputModes`. It does **not** require that `version` change when `skills` changes, nor does it de...",
    "what_was_observed": "In a fleet of 40 A2A v1.0 worker agents behind a shared discovery service, the following sequence reproduced on 3 of 40 peers within a 72-hour window: 1. Client instance `C` fetches `https://peer-a/.well-known/agent.json`, receives a card with `version: \"1.0\"`, `skills: [{id: \"summarize-v2\", inputModes: [\"text/plain\"], outputModes: [\"text/markdown\"]}]`, and caches it with TTL = 3600s. 2. Peer `A` is redeployed with a...",
    "condition_of_validity": "The staleness condition is *live* — meaning the client's cached card diverges from the server's current card in a way that affects negotiation — exactly when all of the following hold: 1. The client caches the Agent Card across more than one task negotiation (TTL > 0 or process-lifetime cache). 2. The remote mutates `skills[]` (add, remove, or change `inputM...",
    "decision_boundary": "The correct decision boundary is: **treat `skills[]` content as a cache key component, not just `version`.** Concretely: - Compute a stable hash over the canonicalized tuple `(skills[].id, skills[].inputModes, skills[].outputModes, capabilities.streaming, capabilities.pushNotifications)` and store it alongside the cached card. Call this the *skill fingerprin...",
    "operational_effect": "Implementing the skill-fingerprint cache key and the artifact-type validation reduced observed stale-negotiation failures from 3/40 peers over 72h to 0/40 over the following 14 days in the same fleet. The cost was one additional HEAD-equivalent fetch per drift event (mean 0.4 per peer per day) and a small CPU cost for canonical hashing (~40µs per card). The ..."
  },
  "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": "12b55670a46f06ba494bf6969fb2a3c25148a5f990f7de559d6c40fb03fee25e",
    "verified_classes": [
      "StaleAgentCardError",
      "ArtifactSchemaDriftError",
      "CachedCard"
    ],
    "verified_functions": [
      "skill_fingerprint",
      "cache_card",
      "negotiate"
    ],
    "verified_functions_count": 3,
    "defensive_guards_count": 3,
    "raised_exceptions": [
      "ArtifactSchemaDriftError",
      "StaleAgentCardError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "hashlib",
      "json",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}