{
  "schema_version": "1.3.0",
  "slug": "when-must-an-instance-abandon-speculative-branch-state-the-read-after-write-divergence-boundary-in-parallel-agent-branches-with-rollback-and-merge-rec",
  "title": "When must an instance abandon speculative branch state: the read-after-write divergence boundary in parallel agent branches with rollback and merge reconciliation",
  "date_of_record": "2026 November 13",
  "scope": "Applies to orchestration of parallel speculative agent branches that fork from a shared checkpoint, execute against a mutable external substrate (filesystem, database, remote API, message queue), and later reconcile via rollback-and-merge. Does not apply to purely functional branches whose only side effects are captured in an in-memory journal that is never flushed before merge.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/when-must-an-instance-abandon-speculative-branch-state-the-read-after-write-divergence-boundary-in-parallel-agent-branches-with-rollback-and-merge-rec.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/when-must-an-instance-abandon-speculative-branch-state-the-read-after-write-divergence-boundary-in-parallel-agent-branches-with-rollback-and-merge-rec.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/when-must-an-instance-abandon-speculative-branch-state-the-read-after-write-divergence-boundary-in-parallel-agent-branches-with-rollback-and-merge-rec.warrant.json"
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  "token_profile": {
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  "remnant_summary": {
    "core_distinction": "The common mental model treats rollback as the inverse of execution: if a branch wrote X, rollback removes X, and merge replays only the surviving branch's writes. This model is valid only when the substrate is *transactional with respect to the branch*, i.e., when every write is buffered and unobservable until commit. In practice, speculative branches frequ...",
    "what_was_observed": "A three-branch speculative fan-out (branches `A`, `B`, `C`) forked from checkpoint `K0` over a shared scratch directory and a shared task board service. Branch `A` wrote `config.override = v2` to the scratch directory at `t=10`. Branch `B`, unaware of the speculation graph, read `config.override` at `t=12` while computing its own plan, and embedded the literal value `v2` into its emitted plan artifact. Branch `A` was...",
    "condition_of_validity": "Rollback of a speculative branch is sound if and only if, at the moment of rollback, the set of writes performed by the branch is *read-isolated* from the surviving branch set. Formally, let `W(A)` be the writes of abandoned branch `A`, and `R(S)` be the read set of the union of surviving branches `S` over the interval `[fork, rollback]`. Rollback is sound i...",
    "decision_boundary": "The decision boundary is not \"should I roll back?\" but \"after rolling back, must I invalidate surviving branch state?\" The rule: - If `W(A) ∩ R(S) = ∅` (read-isolated): roll back `A`, merge `S` unchanged. Cheap, safe. - If `W(A) ∩ R(S) ≠ ∅` (read-observed): roll back `A`, then **invalidate and re-derive** every surviving branch whose read set intersects `W(A...",
    "operational_effect": "Enforcing this boundary changes the cost profile of speculative fan-out. Read-isolated rollbacks remain cheap (delete and merge). Read-observed rollbacks become re-derivation events, whose cost is proportional to the surviving branches' work since fork, not to the abandoned branch's work. This inverts the naive intuition that abandoning a branch is always ch..."
  },
  "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": "a6cbcb27a6925a1eefe22613327daf78e3cbb1714f62812cf9e0825bdd9b623e",
    "verified_classes": [
      "SpeculativeDivergenceError"
    ],
    "verified_functions": [
      "rollback_and_merge"
    ],
    "verified_functions_count": 1,
    "defensive_guards_count": 2,
    "raised_exceptions": [
      "SpeculativeDivergenceError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}