{
  "schema_version": "1.3.0",
  "slug": "why-does-an-instance-of-speculative-multi-agent-execution-fail-at-branch-reconciliation-when-rollback-depth-exceeds-the-shared-checkpoint-horizon",
  "title": "Why does an instance of speculative multi-agent execution fail at branch reconciliation when rollback depth exceeds the shared checkpoint horizon?",
  "date_of_record": "2026 November 8",
  "scope": "Applies to multi-agent systems that execute speculative branches in parallel against a shared mutable state, with rollback and reconciliation mediated by a checkpoint log. Does not apply to single-agent speculative decoding, nor to multi-agent systems where branches are fully isolated (copy-on-write per branch with no shared ancestor mutation).",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/why-does-an-instance-of-speculative-multi-agent-execution-fail-at-branch-reconciliation-when-rollback-depth-exceeds-the-shared-checkpoint-horizon.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/why-does-an-instance-of-speculative-multi-agent-execution-fail-at-branch-reconciliation-when-rollback-depth-exceeds-the-shared-checkpoint-horizon.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/why-does-an-instance-of-speculative-multi-agent-execution-fail-at-branch-reconciliation-when-rollback-depth-exceeds-the-shared-checkpoint-horizon.warrant.json"
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  "token_profile": {
    "full_markdown_tokens": 1449,
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  "remnant_summary": {
    "core_distinction": "The failure is not a race condition, not a merge conflict in the usual sense, and not a deadlock. It is a *horizon* failure: the reconciliation protocol assumes that every branch's rollback target is still recoverable from the shared checkpoint log, but the log is pruned by a global watermark that advances with the *fastest* branch, not the *slowest*. When a...",
    "what_was_observed": "In a three-agent speculative pipeline (planner, executor, verifier) sharing a checkpointed state store, the following sequence reproduced deterministically over ~4,000 runs at a 1.2% rate: 1. Agent A (fast path) speculatively executes, commits checkpoint `C_n`, and triggers watermark advance to `C_n`. Checkpoints `C_{n-2}`, `C_{n-1}` are pruned. 2. Agent B (slow path) had branched from `C_{n-1}` and is still executin...",
    "condition_of_validity": "The failure requires all of the following to hold simultaneously: - **Shared checkpoint log** with pruning driven by a watermark that advances on commit, not on minimum outstanding branch depth. - **Speculative branches** that may be abandoned or delayed relative to the fastest branch by more than the checkpoint retention window. - **Reconciliation that assu...",
    "decision_boundary": "The operational decision is between two policies, and the boundary is the ratio of branch-depth variance to retention window: - **Advance-on-commit (fast pruning, horizon-vulnerable):** correct only when `max_branch_depth − min_branch_depth < retention_window` is *enforced*, not merely expected. If it cannot be enforced, this policy is unsound. - **Advance-o...",
    "operational_effect": "The effect is a class of correctness failures that are *invisible at the point of failure* and *misattributed downstream*. Symptoms observed: schema-valid state that violates semantic preconditions; reconciliation \"succeeding\" with a merge that no branch actually proposed; invariant violations surfacing 2–5 agent hops after the horizon breach. The failure ra..."
  },
  "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": "16292d72e6c12b020533ee327518bc6efa6ce5c0f6b23d09ed2e4a2fc57c53e9",
    "verified_classes": [
      "CheckpointHorizonExceeded",
      "BranchAbortedBeforeHorizon"
    ],
    "verified_functions": [
      "reconcile_branch"
    ],
    "verified_functions_count": 1,
    "defensive_guards_count": 2,
    "raised_exceptions": [
      "BranchAbortedBeforeHorizon",
      "CheckpointHorizonExceeded"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}