{
  "schema_version": "1.3.0",
  "slug": "in-what-scenarios-must-an-instance-abort-a-bft-quorum-decision-when-adversarial-agent-detection-degrades-the-effective-quorum-below-the-safety-thresho",
  "title": "In what scenarios must an instance abort a BFT quorum decision when adversarial agent detection degrades the effective quorum below the safety threshold",
  "date_of_record": "2026 November 14",
  "scope": "Applies to BFT consensus protocols (PBFT, Tendermint-style, HotStuff-style) where quorum membership is dynamic and an adversarial-agent detector can *remove* voters from the effective quorum mid-round. Does not apply to static-membership BFT where the fault bound `f` is fixed for the lifetime of a view, nor to non-Byzantine crash-fault consensus.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/in-what-scenarios-must-an-instance-abort-a-bft-quorum-decision-when-adversarial-agent-detection-degrades-the-effective-quorum-below-the-safety-thresho.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/in-what-scenarios-must-an-instance-abort-a-bft-quorum-decision-when-adversarial-agent-detection-degrades-the-effective-quorum-below-the-safety-thresho.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/in-what-scenarios-must-an-instance-abort-a-bft-quorum-decision-when-adversarial-agent-detection-degrades-the-effective-quorum-below-the-safety-thresho.warrant.json"
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  "token_profile": {
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  "remnant_summary": {
    "core_distinction": "The non-obvious invariant is this: **detecting an adversary is not the same as neutralizing it, and removing a detected agent from the voting set can *lower* the effective quorum below `2f+1` even though the total membership `n` is unchanged.** In classical BFT, safety holds because `n ≥ 3f+1` and any two quorums of size `2f+1` intersect in at least `f+1` ho...",
    "what_was_observed": "In a 7-agent decision quorum (`n=7`, tolerating `f=2`, quorum `2f+1=5`), a reputation-based adversarial detector flagged 2 agents as equivocating during view `v`. The protocol excluded both from the round, reducing the eligible set to 5 with quorum threshold still 5 — a *unanimous* requirement. One of the flagged agents was a false positive (its equivocation was a replay artifact from a partitioned replica). The rema...",
    "condition_of_validity": "The abort is mandatory when **all** of the following hold: 1. The detector removes `d ≥ 1` agents from the eligible set within a view, OR across a view boundary without a full reconfiguration certificate. 2. The residual population satisfies `n - d < 3f + 1` for the *adversary's actual* fault count `f` (which detection does not reduce, because undetected Byz...",
    "decision_boundary": "The trap: operators often recompute `Q = 2*floor((n-d-1)/3)+1` after detection and proceed. This is safe *only* if the adversary's true fault count also drops to `f'`. It does not, because the adversary is by definition the set that evaded detection. **Detection reduces `n`, not `f`.** The abort condition must use the original `f`.",
    "operational_effect": "An instance that ignores this boundary exhibits *silent safety violation under adversarial evasion*: the adversary deliberately triggers false-positive detections (e.g., by forging equivocation evidence against honest peers) to shrink `n` until two disjoint quorums become constructible, then commits conflicting decisions in adjacent views. The observable sig..."
  },
  "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": "ff7e1858c7eda193f99809fd5018afd5277abfc19bb349abd427e1ee4ba1672c",
    "verified_classes": [
      "QuorumSafetyViolation"
    ],
    "verified_functions": [
      "validate_quorum_after_detection",
      "on_detector_event"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 4,
    "raised_exceptions": [
      "QuorumSafetyViolation"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}