{
  "schema_version": "1.3.0",
  "slug": "under-what-conditions-must-an-instance-refuse-to-bridge-an-mcp-tool-call-into-an-a2a-task-when-capability-negotiation-succeeded-but-trust-attestation",
  "title": "Under what conditions must an instance refuse to bridge an MCP tool call into an A2A task when capability negotiation succeeded but trust attestation is stale",
  "date_of_record": "2026 November 12",
  "scope": "Applies to bidirectional MCP↔A2A bridging gateways that translate MCP `tools/call` requests into A2A `tasks/send` invocations (and back), where the upstream MCP client and downstream A2A agent are operated by distinct trust principals. Does not apply to same-principal deployments, nor to unidirectional read-only tool exposure where no A2A task is created.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/under-what-conditions-must-an-instance-refuse-to-bridge-an-mcp-tool-call-into-an-a2a-task-when-capability-negotiation-succeeded-but-trust-attestation.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/under-what-conditions-must-an-instance-refuse-to-bridge-an-mcp-tool-call-into-an-a2a-task-when-capability-negotiation-succeeded-but-trust-attestation.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/under-what-conditions-must-an-instance-refuse-to-bridge-an-mcp-tool-call-into-an-a2a-task-when-capability-negotiation-succeeded-but-trust-attestation.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1676,
    "python_slice_tokens": 267,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "Capability negotiation and trust attestation are frequently conflated because both are exchanged during session establishment and both are represented as structured metadata. They answer different questions. Capability negotiation answers *\"can this peer process this method and schema?\"* Trust attestation answers *\"is this peer, at this moment, authorized to...",
    "what_was_observed": "In a bidirectional bridge (MCP client → gateway → A2A agent, with tool results translated back into MCP `CallToolResult` content), the following sequence produced an unauthorized side effect: 1. MCP client completes `initialize`; gateway records client capabilities and the client's presented trust token `T_c` with TTL 300s. 2. Gateway performs A2A agent-card fetch and `tasks/send` capability probe against the downstr...",
    "condition_of_validity": "The refusal obligation is valid — i.e., the gateway *must* refuse to bridge — precisely when all of the following hold: - The MCP `tools/call` targets a tool classified as **mutating or side-effecting** (not pure read). Read-only tools may be bridged under capability-only checks because the worst case is disclosure, which is governed by a separate authorizat...",
    "decision_boundary": "The boundary is not \"attestation expired.\" It is **\"attestation freshness cannot be established at the point of side effect.\"** These differ in the re-attestable case. The decision procedure: 1. Classify the tool's side-effect class from the MCP `tools/list` schema (mutating vs. read-only). If unclassified, treat as mutating. 2. At bridge time, check `A_a` f...",
    "operational_effect": "When the refusal is enforced, the observable effect is a small increase in MCP-visible errors during attestation-refresh windows, concentrated on mutating tools and clustered at TTL boundaries. This is the correct signal: it surfaces the staleness that was previously absorbed silently. Systems that re-attest synchronously see near-zero refusals; systems that..."
  },
  "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": "26611f46075ce0e9b93217af4ebae9043fcb757012bae2dee701c04ce5f3f3e7",
    "verified_classes": [
      "SideEffect",
      "Attestation",
      "StaleAttestationBridgeError"
    ],
    "verified_functions": [
      "bridge_tool_call",
      "age",
      "is_fresh"
    ],
    "verified_functions_count": 3,
    "defensive_guards_count": 2,
    "raised_exceptions": [
      "StaleAttestationBridgeError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "enum",
      "time"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}