feat(verified): P1-C — split bound_slots_digest into a separate VERIFIED obligation

Proof-object hardening before any serving wiring (review of #663): the "from the
stated quantities" obligation is now THREE separable digests, not folded into
derivation_digest — for replay, audit, and failure localization.

core/epistemic_disclosure/verified_contract.py:
- VerificationProof gains bound_slots_digest (the answer binds to a STATED slot — the
  asked unknown — not a phantom), between derivation_digest and back_substitution_digest.
- VerificationObligation gains requires_bound_slots (VERIFICATION_OBLIGATION strict);
  evaluate_verification adds the REASON_NO_BOUND_SLOTS check.

evals/constraint_oracle/verified_producer.py: populates bound_slots_digest from
unknowns_signature + query_signature + the bound solution, ONLY when the asked unknown
is in the solution (empty for a phantom answer).

A complete derivation does NOT imply the answer bound to a declared slot, so the two are
distinct obligations: test_derivation_digest_alone_is_insufficient_without_bound_slots
proves it (relaxing requires_bound_slots is what admits the gap — load-bearing).

All 7 real r2_gold 'solved' problems still VERIFY (bound_slots populated); wrong=0.
Contract+producer suites 106/0; smoke 90/0. Still off-serving.

core/epistemic_disclosure/verified_contract.py

@@ -64,6 +64,7 @@ class VerificationObligation:
 
     requires_independent_read: bool  # two DISTINCT reader lineages — not the same read twice
     rejects_wrong_read_even_if_solved: bool  # the two reads must CONVERGE — catches a wrong read
+    requires_bound_slots: bool  # the answer binds to the STATED slots (query/unknowns), not phantom ones
     requires_back_substitution: bool  # the answer back-substitutes into the canonical structure
     requires_boundary_clear: bool  # no organ boundary fired in the chain
 
@@ -72,6 +73,7 @@ class VerificationObligation:
 VERIFICATION_OBLIGATION: VerificationObligation = VerificationObligation(
     requires_independent_read=True,
     rejects_wrong_read_even_if_solved=True,
+    requires_bound_slots=True,
     requires_back_substitution=True,
     requires_boundary_clear=True,
 )
@@ -86,6 +88,14 @@ class VerificationProof:
     ``independent_reader_lineage`` must DIFFER (independence), and ``primary_read_digest``
     / ``independent_read_digest`` must MATCH (convergence on one canonical structure).
     Independence + convergence together are what reject a faithful solve of a wrong read.
+
+    The "from the stated quantities" obligation is split into THREE separable digests
+    (P1-C hardening — for replay, audit, and failure localization):
+    ``derivation_digest`` (a solve happened from the structure), ``bound_slots_digest``
+    (the answer binds to a STATED slot — the asked unknown — not a phantom), and
+    ``back_substitution_digest`` (the answer satisfies the constraints). A complete
+    derivation does NOT imply the answer bound to a declared slot, so the two are
+    distinct obligations (``test_derivation_digest_alone_is_insufficient_without_bound_slots``).
     """
 
     source_problem_digest: str  # provenance: hash of the problem text
@@ -93,7 +103,8 @@ class VerificationProof:
     independent_reader_lineage: str  # identity of the independent cross-check reader
     primary_read_digest: str  # canonical structure the primary read produced
     independent_read_digest: str  # canonical structure the independent read produced
-    derivation_digest: str  # the derivation from the STATED quantities
+    derivation_digest: str  # the derivation (solve) from the STATED quantities
+    bound_slots_digest: str  # the answer binds to the STATED slots (asked unknown), not a phantom
     back_substitution_digest: str  # back-substitution into the canonical structure
     boundary_clear: bool  # no organ boundary fired
     contradiction_clear: bool  # no contradiction family fired
@@ -102,6 +113,7 @@ class VerificationProof:
 # Reason codes for a failed obligation — each names exactly one violated rule.
 REASON_READS_NOT_INDEPENDENT = "reads_not_independent"  # same reader lineage twice
 REASON_READS_DISAGREE = "reads_disagree"  # the wrong-read catcher
+REASON_NO_BOUND_SLOTS = "no_bound_slots"  # answer did not bind to a stated slot
 REASON_NO_BACK_SUBSTITUTION = "no_back_substitution"
 REASON_BOUNDARY_FIRED = "boundary_fired"
 REASON_CONTRADICTION_PRESENT = "contradiction_present"
@@ -143,6 +155,9 @@ def evaluate_verification(
     ):
         failed.append(REASON_READS_DISAGREE)
 
+    if obligation.requires_bound_slots and not proof.bound_slots_digest:
+        failed.append(REASON_NO_BOUND_SLOTS)
+
     if obligation.requires_back_substitution and not proof.back_substitution_digest:
         failed.append(REASON_NO_BACK_SUBSTITUTION)
 

evals/constraint_oracle/verified_producer.py

@@ -52,6 +52,8 @@ from core.epistemic_state import EpistemicState
 from evals.constraint_oracle.signature import (
     constraint_setup_signature,
     constraints_signature,
+    query_signature,
+    unknowns_signature,
 )
 from generate.constraint_comprehension.model import ConstraintProblem
 from generate.constraint_comprehension.reader import read_constraint_problem
@@ -139,6 +141,7 @@ def verify_r2(text: str, gold_setup: ConstraintProblem) -> R2VerificationOutcome
     if isinstance(solution, Refusal):
         boundary_clear = False
         derivation_digest = ""
+        bound_slots_digest = ""
         back_substitution_digest = ""
     else:
         boundary_clear = True
@@ -146,6 +149,23 @@ def verify_r2(text: str, gold_setup: ConstraintProblem) -> R2VerificationOutcome
         derivation_digest = _sha(
             repr(("derivation", constraints_signature(primary.constraints), bound))
         )
+        # bound_slots: the answer binds to a STATED slot — the asked unknown — among the
+        # declared unknowns. Empty if the asked unknown was not solved (a phantom answer);
+        # a complete derivation does NOT by itself prove this (P1-C: separable obligation).
+        bound_slots_digest = (
+            _sha(
+                repr(
+                    (
+                        "bound_slots",
+                        unknowns_signature(primary.unknowns),
+                        query_signature(primary.query),
+                        bound,
+                    )
+                )
+            )
+            if primary.query.symbol in solution
+            else ""
+        )
         back_substitution_digest = (
             _sha(repr(("back_substitution", bound)))
             if _back_substitutes(primary, solution)
@@ -159,6 +179,7 @@ def verify_r2(text: str, gold_setup: ConstraintProblem) -> R2VerificationOutcome
         primary_read_digest=_sha(repr(constraint_setup_signature(primary))),
         independent_read_digest=_sha(repr(constraint_setup_signature(gold_setup))),
         derivation_digest=derivation_digest,
+        bound_slots_digest=bound_slots_digest,
         back_substitution_digest=back_substitution_digest,
         boundary_clear=boundary_clear,
         # Setup-only verification has no answer-key path, so no contradiction can arise

tests/test_verified_contract.py

@@ -23,6 +23,7 @@ from core.epistemic_disclosure.verified_contract import (
     REASON_CONTRADICTION_PRESENT,
     REASON_INCOMPLETE_PROOF,
     REASON_NO_BACK_SUBSTITUTION,
+    REASON_NO_BOUND_SLOTS,
     REASON_READS_DISAGREE,
     REASON_READS_NOT_INDEPENDENT,
     REASON_UNRESOLVED_LIMITATION,
@@ -46,6 +47,7 @@ def _valid_proof(**overrides) -> VerificationProof:
         primary_read_digest="canonical_structure_C",
         independent_read_digest="canonical_structure_C",
         derivation_digest="deriv#1",
+        bound_slots_digest="bound#1",
         back_substitution_digest="backsub#1",
         boundary_clear=True,
         contradiction_clear=True,
@@ -96,6 +98,27 @@ def test_verified_requires_back_substitution():
     assert REASON_NO_BACK_SUBSTITUTION in result.failed_checks
 
 
+def test_verified_requires_bound_slots():
+    result = evaluate_verification(_valid_proof(bound_slots_digest=""), limitation=None)
+    assert result.verdict is VerificationVerdict.NOT_VERIFIED
+    assert REASON_NO_BOUND_SLOTS in result.failed_checks
+
+
+def test_derivation_digest_alone_is_insufficient_without_bound_slots():
+    """P1-C hardening: a complete derivation does NOT imply the answer bound to a STATED
+    slot — they are SEPARATE obligations. A proof with a derivation but no bound-slots must
+    not verify; and relaxing exactly the bound-slots obligation stops that check firing
+    (so the obligation is load-bearing, not decoration)."""
+    proof = _valid_proof(derivation_digest="deriv#1", bound_slots_digest="")
+    canonical = evaluate_verification(proof, limitation=None)
+    assert canonical.verdict is VerificationVerdict.NOT_VERIFIED
+    assert REASON_NO_BOUND_SLOTS in canonical.failed_checks
+
+    relaxed = replace(VERIFICATION_OBLIGATION, requires_bound_slots=False)
+    relaxed_result = evaluate_verification(proof, limitation=None, obligation=relaxed)
+    assert REASON_NO_BOUND_SLOTS not in relaxed_result.failed_checks
+
+
 def test_verified_requires_boundary_clear():
     result = evaluate_verification(_valid_proof(boundary_clear=False), limitation=None)
     assert result.verdict is VerificationVerdict.NOT_VERIFIED
@@ -133,6 +156,7 @@ def test_verified_rejects_any_limitation_assessment():
 def test_canonical_obligation_is_fully_strict():
     assert VERIFICATION_OBLIGATION.requires_independent_read
     assert VERIFICATION_OBLIGATION.rejects_wrong_read_even_if_solved
+    assert VERIFICATION_OBLIGATION.requires_bound_slots
     assert VERIFICATION_OBLIGATION.requires_back_substitution
     assert VERIFICATION_OBLIGATION.requires_boundary_clear
 

tests/test_verified_r2_producer.py

@@ -173,6 +173,7 @@ def test_all_proof_digests_populated_on_verified():
         p.primary_read_digest,
         p.independent_read_digest,
         p.derivation_digest,
+        p.bound_slots_digest,
         p.back_substitution_digest,
     ):
         assert digest, "every replay-critical digest must be populated on a VERIFIED proof"