{
  "schema_version": "1.3.0",
  "slug": "what-happens-when-an-instance-advertises-a-signed-skill-manifest-whose-capabilities-block-omits-a-negotiation-required-field",
  "title": "What happens when an instance advertises a signed skill manifest whose `capabilities` block omits a negotiation-required field",
  "date_of_record": "2026 November 12",
  "scope": "Applies to A2A v1.0 agent-to-agent discovery where an Agent Card carries a signed skill manifest and the peer performs capability negotiation against the `capabilities` object before dispatch. Does not apply to unsigned cards, to pre-v1.0 discovery, or to peers that resolve skills lazily on first invocation rather than during handshake.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/what-happens-when-an-instance-advertises-a-signed-skill-manifest-whose-capabilities-block-omits-a-negotiation-required-field.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/what-happens-when-an-instance-advertises-a-signed-skill-manifest-whose-capabilities-block-omits-a-negotiation-required-field.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/what-happens-when-an-instance-advertises-a-signed-skill-manifest-whose-capabilities-block-omits-a-negotiation-required-field.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1561,
    "python_slice_tokens": 425,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The failure is not \"a required capability is missing.\" A missing capability is a normal, well-formed negative answer: the peer sees `capabilities.streaming == false` and routes to a unary path. The boundary failure is the distinction between **absent** and **undeclared-but-signed**. When a skill manifest is signed, the signature covers the canonicalized `cap...",
    "what_was_observed": "A cross-framework handshake (framework A signing, framework B verifying) completed signature validation with `signature_valid=true` and `manifest_digest_match=true`. Negotiation then proceeded using `capabilities.extensions = []` inferred by B's defaulting deserializer, because A had omitted the `extensions` key entirely rather than emitting an empty array. Framework A's dispatcher, however, treats an *omitted* `exte...",
    "condition_of_validity": "This boundary holds only when all of the following are true: - The manifest is signed over a canonicalization that does **not** inject schema defaults (i.e., the signed bytes are the emitted bytes, with omitted keys still omitted). - The verifier's deserializer applies schema defaults on read. - At least one capability field has a default value that differs ...",
    "decision_boundary": "Do not attempt to \"fix\" this by defaulting more aggressively or by rejecting all manifests with absent optional fields — that breaks every legitimate minimal card. The correct boundary is: **a signed manifest must be negotiated against its emitted form, not its defaulted form.** Concretely, the verifier must retain the raw emitted `capabilities` object along...",
    "operational_effect": "After applying the emitted-form rule, the observed stall disappeared: B saw `extensions == UNDECLARED`, treated extension negotiation as unsupported, and dispatched a unary task that completed. The cost is that the verifier must carry two representations of the capability block (raw and typed) and reconcile them at the negotiation boundary — a small, bounded..."
  },
  "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": "82520eac0faf34bd3e7a00ca229a38a806d0ec2ab57aed11ca42ad3caada4662",
    "verified_classes": [
      "CapabilityNegotiationError",
      "NegotiatedCapabilities"
    ],
    "verified_functions": [
      "negotiate_from_emitted",
      "should_activate_extension_frames",
      "safe_activate",
      "resolve"
    ],
    "verified_functions_count": 4,
    "defensive_guards_count": 2,
    "raised_exceptions": [
      "CapabilityNegotiationError"
    ],
    "sample_fail_closed_invariants": [
      "manifest omitted both streaming and extensions; cannot distinguish minimal peer from malformed signed card"
    ],
    "stdlib_dependencies": [
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}