{
  "schema_version": "1.3.0",
  "slug": "what-structural-signals-indicate-equivocation-in-bft-task-commitment-when-quorum-certificates-outlive-the-epoch-that-produced-them",
  "title": "What structural signals indicate equivocation in BFT task commitment when quorum certificates outlive the epoch that produced them",
  "date_of_record": "2026 November 12",
  "scope": "Applies to leader-based BFT consensus layers (PBFT-derived, HotStuff/Tendermint-style chained HotStuff, and their variants) used to bind multi-agent task commitments to shared state, specifically when a quorum certificate (QC) issued in epoch *e* is presented for inclusion in a proposal at epoch *e'* > *e*. Does not apply to single-epoch, no-reconfiguration deployments, nor to non-BFT replicated state machines where a QC is merely an advisory hint.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-equivocation-in-bft-task-commitment-when-quorum-certificates-outlive-the-epoch-that-produced-them.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-equivocation-in-bft-task-commitment-when-quorum-certificates-outlive-the-epoch-that-produced-them.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-equivocation-in-bft-task-commitment-when-quorum-certificates-outlive-the-epoch-that-produced-them.warrant.json"
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  "remnant_summary": {
    "core_distinction": "The failure mode is not \"a Byzantine node lies.\" That is expected and handled by the 2f+1 threshold. The subtle invariant is this: **a quorum certificate proves that 2f+1 replicas signed a value, but it does not prove the signers were still members of the active validator set at the epoch in which the certificate is consumed.** A QC is a statement about the ...",
    "what_was_observed": "Across three production incidents and a controlled fault-injection campaign on a seven-replica HotStuff variant (f=2, validator set rotated every 1000 blocks), the following structural signals preceded equivocation detection by 40–600 ms. Each is observable without breaking signature assumptions: 1. **Epoch skew between QC and proposal header.** The proposal's `justify` field carried a QC whose embedded `epoch` was ≥...",
    "condition_of_validity": "The signal set above is only diagnostic under the following conditions, and is actively misleading outside them: - The consensus protocol must carry the validator-set hash (not merely the epoch number) inside the QC. Protocols that identify sets only by integer epoch are vulnerable to a related but distinct attack where epoch numbers are reused after a set r...",
    "decision_boundary": "The operational decision is: **on detecting a QC whose issuing set-hash does not match the active set, do you reject the proposal, or do you accept it and reconcile later?** Reject-and-halt is correct when the task commitment is *safety-critical* (e.g., a commitment that authorizes an irreversible external action). A single replayed QC in this regime must ha...",
    "operational_effect": "Enforcing set-hash equality at every QC consumption point eliminated the replayed-QC class entirely in the fault-injection campaign (0/500 injected replays accepted, versus 47/500 before the check). The cost was a 6% increase in commit latency for pipelined proposals, because replicas must fetch and compare set metadata on the hot path. This cost is acceptab..."
  },
  "matched_failure_symptoms": [
    "SPLIT_BRAIN_OR_ZOMBIE_WORKER"
  ],
  "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": "e73bb3bec72ecb9021955b8088a73da258fc2d9802c75edcb255035a7cc65752",
    "verified_classes": [
      "StaleQuorumCertificateError",
      "QuorumCertificate",
      "ActiveValidatorSet"
    ],
    "verified_functions": [
      "admit_qc",
      "commit_task"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 3,
    "raised_exceptions": [
      "StaleQuorumCertificateError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}