{
  "schema_version": "1.3.0",
  "slug": "what-happens-when-an-instance-of-a-speculative-plan-commits-a-partial-branch-under-byzantine-quorum-drift",
  "title": "What happens when an instance of a speculative plan commits a partial branch under Byzantine quorum drift",
  "date_of_record": "2026 November 13",
  "scope": "Applies to multi-agent planners where a coordinator speculatively executes candidate branches in parallel and commits one via a Byzantine fault-tolerant (BFT) quorum protocol (e.g., PBFT-style prepare/commit with 3f+1 replicas). Does not apply to single-agent planners, to non-speculative serial pipelines, or to protocols with a trusted coordinator whose liveness is not subject to quorum drift.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/what-happens-when-an-instance-of-a-speculative-plan-commits-a-partial-branch-under-byzantine-quorum-drift.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/what-happens-when-an-instance-of-a-speculative-plan-commits-a-partial-branch-under-byzantine-quorum-drift.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/what-happens-when-an-instance-of-a-speculative-plan-commits-a-partial-branch-under-byzantine-quorum-drift.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1417,
    "python_slice_tokens": 225,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The failure is not \"a Byzantine agent proposed a bad plan.\" It is the interaction between **speculative execution** (a branch's side effects are materialized before the commit decision is final) and **quorum drift** (the set of replicas that form a quorum at prepare-time differs from the set that forms a quorum at commit-time). Speculation assumes the commit...",
    "what_was_observed": "During a coordinator failover under load, the following sequence was captured (replica IDs anonymized; N=7, f=2, quorum=5): 1. View v=12: coordinator speculatively executes branch `B3` on 6 replicas; 4 of them durably write `B3`'s effects to their local effect log (optimistic apply) before the prepare phase completes. 2. A network partition isolates the coordinator; a view change to v=13 fires. The new quorum is `{R0...",
    "condition_of_validity": "This boundary is reachable only when *all* of the following hold simultaneously: - Speculative branches produce **externally observable or non-idempotent side effects** (lease acquisition, ledger writes, message emission) before commit finalization. Pure-compute speculation is immune. - The BFT protocol uses **view-scoped quorum certificates** without carryi...",
    "decision_boundary": "The operative rule for an agent operating this class of system: > **Do not speculate on a branch whose effects are non-idempotent and non-compensable unless the commit certificate carries the speculation epoch and the effect log supports epoch-scoped abort.** Concretely, before launching a speculative branch, classify its effects: - **Idempotent + compensabl...",
    "operational_effect": "Systems that crossed this boundary exhibited three signatures, in order: (1) a *silent* divergence in effect logs across replicas that passed all BFT safety checks (because safety checks validate certificates, not effect logs); (2) a *livelock* on recovery when the coordinator attempted to reconcile `B3` and `B5` and found neither abort nor commit path admis..."
  },
  "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": "261799b5d0cce40ca1aa77ac53b08d53a60d92c057ddca03e0abad534b5096c2",
    "verified_classes": [
      "PartialCommitUnderQuorumDrift",
      "EffectClass"
    ],
    "verified_functions": [
      "guard_speculative_branch",
      "attempt_speculative_commit"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 3,
    "raised_exceptions": [
      "PartialCommitUnderQuorumDrift"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}