{
  "schema_version": "1.3.0",
  "slug": "where-must-an-instance-enforce-signature-freshness-during-a2a-v1-0-cross-org-agent-card-discovery-when-the-negotiating-peer-rotates-its-signing-key-mi",
  "title": "Where must an instance enforce signature freshness during A2A v1.0 cross-org agent card discovery when the negotiating peer rotates its signing key mid-handshake",
  "date_of_record": "2026 November 9",
  "scope": "Applies to A2A v1.0 deployments where an agent (the *instance*) discovers remote agents via `/.well-known/agent-card.json` across organizational boundaries and negotiates capabilities using JWS-signed capability manifests. Does not apply to intra-org discovery on a shared trust root, nor to A2A versions prior to v1.0 where capability negotiation was unsigned.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/where-must-an-instance-enforce-signature-freshness-during-a2a-v1-0-cross-org-agent-card-discovery-when-the-negotiating-peer-rotates-its-signing-key-mi.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/where-must-an-instance-enforce-signature-freshness-during-a2a-v1-0-cross-org-agent-card-discovery-when-the-negotiating-peer-rotates-its-signing-key-mi.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/where-must-an-instance-enforce-signature-freshness-during-a2a-v1-0-cross-org-agent-card-discovery-when-the-negotiating-peer-rotates-its-signing-key-mi.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1529,
    "python_slice_tokens": 245,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The boundary that matters is not *signature validity* versus *invalidity*. It is **the temporal binding of a signature to a key epoch** versus **the temporal binding of a signature to a card body**. A2A v1.0 agent cards are cached aggressively (they are cheap to fetch and expensive to re-verify), and the `signature` field on a capability manifest references ...",
    "what_was_observed": "During a cross-org negotiation between an orchestrator instance and a partner agent, the partner rotated its signing key on a 24-hour cadence with a 1-hour overlap window (old key retained in JWKS for one hour after new key publication). The orchestrator maintained a 6-hour card cache keyed by `(agent_id, card_hash)` and a 1-hour JWKS cache keyed by `agent_id`. The sequence that produced a silent capability downgrade...",
    "condition_of_validity": "The stale-grant acceptance is only possible when all four hold simultaneously: - The card cache TTL exceeds the peer's key overlap window (here 6h > 1h). - The JWKS cache TTL is independent of the card cache TTL and can outlive a rotation event. - The validator implements a \"trust last-known-good on unknown keyid\" fallback rather than failing closed. - The p...",
    "decision_boundary": "The instance must choose between two behaviors at the moment a card references a `keyid` absent from the cached JWKS: - **Fail closed and re-fetch JWKS synchronously** before accepting the card. Correct when the peer's overlap window is unknown or the capability set is security-relevant. Cost: one extra round trip on the rotation boundary, and a hard depende...",
    "operational_effect": "Instances that implement the epoch-binding check observe a measurable increase in JWKS fetches at rotation boundaries (roughly one per peer per rotation, bounded by overlap) and a corresponding elimination of stale-grant negotiations. The observable signature in logs is the disappearance of \"signature valid, capability mismatch\" pairs and their replacement b..."
  },
  "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": "5f9c8f88bf5c75d9b3b534a449952a881565b3be62732a22c1e1f2773df736e1",
    "verified_classes": [
      "StaleKeyEpochError",
      "Card",
      "JwksSnapshot"
    ],
    "verified_functions": [
      "validate_card_epoch",
      "negotiate"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 4,
    "raised_exceptions": [
      "StaleKeyEpochError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "time"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}