diff --git a/evals/adr_0243_cognitive_lifecycle/propositional_falsifier.py b/evals/adr_0243_cognitive_lifecycle/propositional_falsifier.py
new file mode 100644
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+++ b/evals/adr_0243_cognitive_lifecycle/propositional_falsifier.py
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+"""ADR-0243 Phase 4 — decisive falsifier: field relaxation decoder vs ROBDD gold.
+
+The propositional slice of ADR-0243's falsifiability benchmark (plan §5 Phase 4).
+Two independent engines decide the SAME propositional entailment problems:
+
+* **Field decoder** — :func:`core.physics.cognitive_lifecycle.propositional_entails`
+  reads the ground energy of a Cl(4,1) wave field relaxed on a diagonal penalty
+  Hamiltonian (ADR-0243 §2.2). ``entailed`` ⇔ ``premises ∧ ¬conclusion`` has
+  ground energy > 0 (UNSAT).
+* **Gold** — :func:`generate.proof_chain.entail.evaluate_entailment` decides
+  ``(⋀premises) → query`` by an exact ROBDD tautology check (ADR-0201 keystone).
+  A canonical, complete, mechanism-disjoint decision procedure.
+
+The bridge renders each CNF clause to the gold's formula syntax (``a | ~b | c``;
+premises are one string per clause) so both engines decide byte-for-byte the same
+problem, and the gold is genuinely independent — not the field decoder checking
+itself.
+
+**What wrong == 0 means (plan's decisive falsifier).** On the satisfiable-premise
+panel the two verdicts are directly comparable: ``field.entailed`` ⇔
+``gold.outcome is ENTAILED``. A single divergence confirms *"the field engine is
+NOT the reasoner today"* on this domain; zero divergence over the panel is the
+evidence that the decode-not-generate thesis holds on checkable propositional
+logic. Inconsistent premises are handled honestly, not swept under the rug: the
+field decoder discloses ``satisfiable_premises=False`` (vacuous ex-falso
+entailment) exactly where the gold returns ``REFUSED`` — a matched refusal, not a
+disagreement. Out-of-regime problems (> 5 atoms) are where the field decoder
+*refuses* by construction while the gold still decides — the honest ID/OOD scope
+boundary, in the propositional domain.
+
+Off-serving: lives under ``evals/`` only; never imported by ``chat/runtime.py``.
+Deterministic: the panel is enumerated (no wall-clock, no unseeded randomness).
+"""
+
+from __future__ import annotations
+
+import itertools
+from dataclasses import dataclass
+from typing import Any, Iterator, Sequence
+
+from core.physics.cognitive_lifecycle import (
+    HamiltonianCompileError,
+    PropositionalProblem,
+    propositional_entails,
+)
+from generate.proof_chain.entail import Entailment, evaluate_entailment
+
+# A CNF clause: disjunction of (atom, polarity) literals — the shape
+# ``PropositionalProblem.clauses`` and ``propositional_entails``'s conclusion
+# both accept. Defined locally rather than importing the module's non-exported
+# ``Clause`` alias.
+Clause = tuple[tuple[str, bool], ...]
+
+__all__ = [
+    "FalsifierCase",
+    "render_clause",
+    "run_propositional_falsifier",
+]
+
+
+def render_clause(clause: Clause) -> str:
+    """Render a CNF clause (disjunction of literals) in the gold's syntax.
+
+    ``(("a", True), ("b", False))`` → ``"a | ~b"``. A single literal renders
+    bare (``"a"`` / ``"~a"``); the ROBDD parser treats ``|`` as OR, ``~`` as NOT.
+    """
+    if not clause:
+        raise ValueError("render_clause: empty clause has no propositional meaning")
+    return " | ".join(atom if polarity else f"~{atom}" for atom, polarity in clause)
+
+
+def _premise_strings(problem: PropositionalProblem) -> tuple[str, ...]:
+    return tuple(render_clause(c) for c in problem.clauses)
+
+
+@dataclass(frozen=True, slots=True)
+class FalsifierCase:
+    """One field-vs-gold comparison record (JSON-safe via :meth:`as_dict`)."""
+
+    premises: tuple[str, ...]
+    conclusion: str
+    field_entailed: bool
+    field_premises_satisfiable: bool
+    gold_outcome: str
+    gold_reason: str
+    lane: str  # "id" | "refusal_parity"
+    agree: bool
+
+    def as_dict(self) -> dict[str, Any]:
+        return {
+            "premises": list(self.premises),
+            "conclusion": self.conclusion,
+            "field_entailed": self.field_entailed,
+            "field_premises_satisfiable": self.field_premises_satisfiable,
+            "gold_outcome": self.gold_outcome,
+            "gold_reason": self.gold_reason,
+            "lane": self.lane,
+            "agree": self.agree,
+        }
+
+
+def _atom_literals(atoms: Sequence[str]) -> list[Clause]:
+    """All 1- and 2-literal clauses over ``atoms`` (a 2-literal clause never
+    repeats an atom — that would be a tautological or contradictory clause the
+    field compiler rejects as a duplicate literal)."""
+    singles: list[Clause] = [((a, p),) for a in atoms for p in (True, False)]
+    pairs: list[Clause] = []
+    for a, b in itertools.combinations(atoms, 2):
+        for pa in (True, False):
+            for pb in (True, False):
+                pairs.append(((a, pa), (b, pb)))
+    return singles + pairs
+
+
+def _enumerate_problems(
+    atoms: tuple[str, ...],
+    *,
+    max_clauses: int,
+) -> Iterator[tuple[PropositionalProblem, Clause]]:
+    """Deterministically enumerate (problem, conclusion) pairs over ``atoms``.
+
+    Premise sets are size 1..``max_clauses`` combinations of the atom clauses;
+    the conclusion ranges over every single literal. Order is fully determined
+    by ``itertools`` iteration over the sorted atom clauses — no randomness.
+    """
+    clauses = _atom_literals(atoms)
+    conclusions: list[Clause] = [((a, p),) for a in atoms for p in (True, False)]
+    for size in range(1, max_clauses + 1):
+        for premise_combo in itertools.combinations(clauses, size):
+            problem = PropositionalProblem(atoms=atoms, clauses=tuple(premise_combo))
+            for conclusion in conclusions:
+                yield problem, conclusion
+
+
+def run_propositional_falsifier(
+    *,
+    atoms: tuple[str, ...] = ("a", "b", "c"),
+    max_clauses: int = 2,
+    ood_atoms: tuple[str, ...] = ("a", "b", "c", "d", "e", "f"),
+) -> dict[str, Any]:
+    """Score the field decoder against the ROBDD gold; return a JSON-safe artifact.
+
+    ``wrong`` counts ID-lane divergences (``field.entailed`` ≠
+    ``gold is ENTAILED`` on satisfiable premises) plus refusal-parity mismatches
+    (inconsistent premises where the field failed to disclose unsatisfiable
+    premises, or the gold did not refuse). ``ood_field_refused`` records that a
+    > 5-atom problem is rejected by the field decoder (out of its exact regime)
+    while remaining decidable for the gold.
+    """
+    id_cases: list[FalsifierCase] = []
+    refusal_cases: list[FalsifierCase] = []
+    wrong = 0
+
+    for problem, conclusion in _enumerate_problems(atoms, max_clauses=max_clauses):
+        field = propositional_entails(problem, conclusion)
+        gold = evaluate_entailment(_premise_strings(problem), render_clause(conclusion))
+
+        if gold.outcome is Entailment.REFUSED:
+            # Gold refuses only on inconsistent premises here (input is always
+            # in-regime propositional). The field decoder must disclose the same
+            # via satisfiable_premises=False rather than assert real entailment.
+            agree = field.satisfiable_premises is False
+            refusal_cases.append(
+                FalsifierCase(
+                    premises=_premise_strings(problem),
+                    conclusion=render_clause(conclusion),
+                    field_entailed=field.entailed,
+                    field_premises_satisfiable=field.satisfiable_premises,
+                    gold_outcome=gold.outcome.value,
+                    gold_reason=gold.reason,
+                    lane="refusal_parity",
+                    agree=agree,
+                )
+            )
+            if not agree:
+                wrong += 1
+            continue
+
+        # Satisfiable-premise ID lane: field.entailed ⇔ gold is ENTAILED.
+        gold_entailed = gold.outcome is Entailment.ENTAILED
+        agree = field.entailed == gold_entailed
+        id_cases.append(
+            FalsifierCase(
+                premises=_premise_strings(problem),
+                conclusion=render_clause(conclusion),
+                field_entailed=field.entailed,
+                field_premises_satisfiable=field.satisfiable_premises,
+                gold_outcome=gold.outcome.value,
+                gold_reason=gold.reason,
+                lane="id",
+                agree=agree,
+            )
+        )
+        if not agree:
+            wrong += 1
+
+    # OOD: > 5 atoms is outside the field decoder's exact ≤ 32-assignment regime.
+    # It must refuse (typed) rather than guess; the gold still decides.
+    ood_field_refused = False
+    ood_gold_decided = False
+    ood_conclusion: Clause = ((ood_atoms[0], True),)
+    ood_clauses: tuple[Clause, ...] = tuple(((a, True),) for a in ood_atoms)
+    try:
+        PropositionalProblem(atoms=ood_atoms, clauses=ood_clauses)
+    except HamiltonianCompileError:
+        ood_field_refused = True
+    ood_gold = evaluate_entailment(
+        tuple(render_clause(c) for c in ood_clauses), render_clause(ood_conclusion)
+    )
+    ood_gold_decided = ood_gold.outcome is not Entailment.REFUSED
+
+    return {
+        "wrong": wrong,
+        "id_case_count": len(id_cases),
+        "id_disagreements": [c.as_dict() for c in id_cases if not c.agree],
+        "refusal_parity_count": len(refusal_cases),
+        "refusal_parity_mismatches": [c.as_dict() for c in refusal_cases if not c.agree],
+        "ood_field_refused": ood_field_refused,
+        "ood_gold_decided": ood_gold_decided,
+        "atoms": list(atoms),
+        "max_clauses": max_clauses,
+    }
diff --git a/tests/test_adr_0243_propositional_falsifier.py b/tests/test_adr_0243_propositional_falsifier.py
new file mode 100644
index 00000000..89b7ce1a
--- /dev/null
+++ b/tests/test_adr_0243_propositional_falsifier.py
@@ -0,0 +1,82 @@
+"""ADR-0243 Phase 4 — decisive falsifier test (field decoder vs ROBDD gold).
+
+The load-bearing evidence of the arc: the Cl(4,1) field relaxation decoder must
+agree with the independent ROBDD gold on every satisfiable-premise propositional
+problem in the enumerated panel (``wrong == 0``), match its refusal on
+inconsistent premises, and honestly refuse out-of-regime (> 5-atom) problems the
+gold still decides. A single ID divergence would confirm the field engine is not
+the reasoner on this domain.
+"""
+
+from __future__ import annotations
+
+import ast
+import json
+from pathlib import Path
+
+from evals.adr_0243_cognitive_lifecycle.propositional_falsifier import (
+    render_clause,
+    run_propositional_falsifier,
+)
+from generate.proof_chain.entail import Entailment, evaluate_entailment
+
+_ROOT = Path(__file__).resolve().parents[1]
+
+
+def test_render_clause_matches_gold_syntax():
+    assert render_clause((("a", True),)) == "a"
+    assert render_clause((("a", False),)) == "~a"
+    assert render_clause((("a", True), ("b", False), ("c", True))) == "a | ~b | c"
+
+
+def test_field_decoder_matches_robdd_gold_wrong_zero():
+    """Decisive falsifier: zero field-vs-gold divergence over the panel."""
+    artifact = run_propositional_falsifier()
+    # Both comparison lanes are actually exercised (not a vacuous pass).
+    assert artifact["id_case_count"] > 0
+    assert artifact["refusal_parity_count"] > 0
+    # The load-bearing assertion.
+    assert artifact["wrong"] == 0, (
+        f"field decoder diverged from ROBDD gold: "
+        f"id_disagreements={artifact['id_disagreements'][:3]} "
+        f"refusal_mismatches={artifact['refusal_parity_mismatches'][:3]}"
+    )
+    assert artifact["id_disagreements"] == []
+    assert artifact["refusal_parity_mismatches"] == []
+
+
+def test_out_of_regime_is_field_refused_but_gold_decidable():
+    """ID/OOD scope boundary: > 5 atoms → field refuses, gold still decides."""
+    artifact = run_propositional_falsifier()
+    assert artifact["ood_field_refused"] is True
+    assert artifact["ood_gold_decided"] is True
+
+
+def test_falsifier_artifact_is_deterministic_and_json_safe():
+    a = json.dumps(run_propositional_falsifier(), sort_keys=True)
+    b = json.dumps(run_propositional_falsifier(), sort_keys=True)
+    assert a == b
+    assert json.loads(a)["wrong"] == 0
+
+
+def test_gold_is_a_genuinely_independent_mechanism():
+    """Sanity that the gold decides these canonical patterns as expected —
+    it is the ROBDD tautology check, not the field decoder in disguise."""
+    # modus ponens: (a→b) i.e. (~a | b), and a  ⊨ b
+    assert evaluate_entailment(("~a | b", "a"), "b").outcome is Entailment.ENTAILED
+    # p ∨ q ⊭ p
+    assert evaluate_entailment(("a | b",), "a").outcome is Entailment.UNKNOWN
+    # inconsistent premises refuse (no ex-falso)
+    assert evaluate_entailment(("a", "~a"), "b").outcome is Entailment.REFUSED
+
+
+def test_falsifier_is_not_serve_wired():
+    """Off-serving: chat/runtime.py must never import this eval package."""
+    runtime_src = (_ROOT / "chat" / "runtime.py").read_text(encoding="utf-8")
+    tree = ast.parse(runtime_src)
+    for node in ast.walk(tree):
+        if isinstance(node, ast.ImportFrom) and node.module:
+            assert "adr_0243_cognitive_lifecycle" not in node.module
+        if isinstance(node, ast.Import):
+            for alias in node.names:
+                assert "adr_0243_cognitive_lifecycle" not in alias.name