diff --git a/proof/SPEC.md b/proof/SPEC.md
index 24925c2ea..d95bcfda0 100644
--- a/proof/SPEC.md
+++ b/proof/SPEC.md
@@ -158,7 +158,9 @@ verdict was earned.
   whether the **closing** solver was a stand-in. A cache hit that dropped the
   marker would launder an unearned proof into an unmarked one.
 - A relying party that will act on a proof **MUST** check it. Verifying the
-  envelope establishes the signature, not that anything was proved.
+  envelope establishes the signature, not that anything was proved. The marker
+  therefore rides in the signed receipt as `closed_by_stub` (§6.1), so a party
+  holding only the artifact can make that check without trusting the prover.
 - A stand-in **MUST NOT** be presented as a decision procedure in any published
   figure or claim derived from a run.
 
@@ -187,6 +189,8 @@ baseline_uj       = uint                 ; frontier-only cost of this goal
 energy_provenance = "HwShunt" | "ModelBased" | "Estimator"
 spec_grounding    = "Ungrounded" | "HumanReviewed" | "CrossChecked"
 from_cache        = 0 | 1
+closed_by_stub    = 1                    ; omitted when the closer was real (§5.2)
+ceiling_uj        = uint                 ; omitted when the run was unbounded
 steward           = the signer's id (the COSE kid)
 ```
 
@@ -196,6 +200,30 @@ says, in the signed artifact itself, that the statement was not validated
 against intent. Proof receipts are byte-compatible with the family's JCR-1
 verifiers.
 
+### 6.1 `closed_by_stub` — the verdict's own qualifier
+
+An implementation MUST emit `closed_by_stub = 1` when the rung that closed the
+goal was a reference stand-in (§5.2), and MUST omit the field otherwise.
+
+§5.2 already requires a relying party to check this before acting on a proof.
+Until it entered the signed core the marker lived only on the in-process result,
+so a party holding **only the receipt** — which is the entire purpose of sealing
+one — could not perform the check the specification asks of them. A verifier
+that must consult the prover to learn whether a proof is real is not a verifier.
+
+`closed_by` does not answer this. It names a **tier**, and the same tag covers a
+real decision procedure on one ladder and a stand-in on another; `T0` is a
+propositional decider in a real ladder and a `GoalKind` gate in the reference
+one. Nor do the other qualifiers: `energy_provenance` qualifies the *energy* and
+`spec_grounding` the *intent*. This is the only field that says whether the
+**verdict** was earned.
+
+Omit-when-false is normative, not an optimization. It makes the field free for
+honest proofs: a receipt closed by a real solver canonicalizes to exactly the
+bytes it did before this field existed, so every such receipt sealed under an
+earlier revision still verifies. The byte cost falls only on receipts that were
+making an unearned claim.
+
 ## 7. The cache (RECOMMENDED)
 
 A verified proof SHOULD be memoized by goal id. An identical goal then closes for
diff --git a/proof/conformance/v1/receipts.jsonl b/proof/conformance/v1/receipts.jsonl
index 9c4cebeb6..ef1d34d9a 100644
--- a/proof/conformance/v1/receipts.jsonl
+++ b/proof/conformance/v1/receipts.jsonl
@@ -1,4 +1,4 @@
-{"closed_by":"T0","envelope_hex":"d2845821a2012704581b6469643a6578616d706c653a70726f6f662d7265666572656e6365a0590156ac67676f616c5f69647840653161316333326461653066323564323565316134316266323432343535613139303837343130646437636339643138646230303266386336643839393735386773746577617264781b6469643a6578616d706c653a70726f6f662d7265666572656e636567766572646963746670726f76656468617274696661637478403761313530353464313962343730363932663866303366666561653839653863343431353235363263303464323937336435373334343666353937323435613968746f74616c5f756a183269636c6f7365645f6279625430697761737465645f756a006a66726f6d5f6361636865006b626173656c696e655f756a1a02faf0806d70726f6f665f726563656970746770726f6f662f316e737065635f67726f756e64696e676a556e67726f756e64656471656e657267795f70726f76656e616e636569457374696d61746f725840fbaa829eb27e79033ed6d80c5397972e09f4656f954565de7a6853773e0bbd28959e1a7b221e447ef56e60e6124161500ff03027f00403763bc689434ced930d","goal":"x = x","signed_core_hex":"ac67676f616c5f69647840653161316333326461653066323564323565316134316266323432343535613139303837343130646437636339643138646230303266386336643839393735386773746577617264781b6469643a6578616d706c653a70726f6f662d7265666572656e636567766572646963746670726f76656468617274696661637478403761313530353464313962343730363932663866303366666561653839653863343431353235363263303464323937336435373334343666353937323435613968746f74616c5f756a183269636c6f7365645f6279625430697761737465645f756a006a66726f6d5f6361636865006b626173656c696e655f756a1a02faf0806d70726f6f665f726563656970746770726f6f662f316e737065635f67726f756e64696e676a556e67726f756e64656471656e657267795f70726f76656e616e636569457374696d61746f72","total_uj":50,"wire":{"artifact":"7a15054d19b470692f8f03ffeae89e8c44152562c04d2973d573446f597245a9","baseline_uj":50000000,"closed_by":"T0","energy_provenance":"Estimator","from_cache":0,"goal_id":"e1a1c32dae0f25d25e1a41bf242455a19087410dd7cc9d18db002f8c6d899758","proof_receipt":"proof/1","spec_grounding":"Ungrounded","steward":"did:example:proof-reference","total_uj":50,"verdict":"proved","wasted_uj":0}}
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diff --git a/proof/proof-rs/crates/proof-receipt/src/lib.rs b/proof/proof-rs/crates/proof-receipt/src/lib.rs
index 788d99f95..b104bab71 100644
--- a/proof/proof-rs/crates/proof-receipt/src/lib.rs
+++ b/proof/proof-rs/crates/proof-receipt/src/lib.rs
@@ -61,6 +61,23 @@ pub fn to_jcr1_wire(r: &CascadeResult, steward: &str) -> Value {
     if let Some(c) = r.ceiling_uj {
         obj.insert("ceiling_uj".into(), json!(c));
     }
+    // Whether the rung that CLOSED the goal discharges nothing (SPEC §5.2).
+    //
+    // §5.2 requires a relying party to check this before acting on a proof, but
+    // until now it lived only on the in-process result — so anyone holding just
+    // the receipt, which is the whole point of sealing one, could not perform
+    // the check the spec asks of them. A stand-in-closed receipt is honestly
+    // signed and substantively empty; without this field nothing in the bytes
+    // says so, and `closed_by` does not: it names a TIER, and the same tag
+    // covers a real decision procedure on one ladder and a stand-in on another.
+    //
+    // Emitted only when true, so a receipt closed by a real solver
+    // canonicalizes to exactly the bytes it always did and every such receipt
+    // sealed before this field existed still verifies unchanged. The cost falls
+    // entirely on receipts that were making an unearned claim.
+    if r.closed_by_stub {
+        obj.insert("closed_by_stub".into(), json!(1));
+    }
     obj.insert("steward".into(), json!(steward));
     Value::Object(obj)
 }
@@ -131,6 +148,55 @@ mod tests {
         assert!(o.contains_key("baseline_uj") && o.contains_key("wasted_uj"));
     }
 
+    /// A stand-in-closed receipt says so in the bytes a third party receives.
+    ///
+    /// SPEC §5.2 requires a relying party to check whether the closing rung
+    /// discharged anything; §6.1 puts the marker in the signed core so they can
+    /// do it holding only the artifact. Without this the pack ships a receipt
+    /// asserting an open conjecture is proved, with nothing to qualify it.
+    #[test]
+    fn a_stand_in_closed_receipt_declares_itself_on_the_wire() {
+        let r = prove_one("open conjecture", GoalKind::Hard);
+        assert!(r.proved && r.closed_by_stub, "fixture must be stub-closed");
+        let wire = to_jcr1_wire(&r, "did:example:p");
+        assert_eq!(
+            wire.as_object().unwrap().get("closed_by_stub"),
+            Some(&json!(1)),
+            "a receipt closed by a rung that discharges nothing must say so"
+        );
+    }
+
+    /// ...and the field is free for an honest proof.
+    ///
+    /// Omit-when-false is what makes this revision non-breaking: a receipt
+    /// closed by a real decision procedure canonicalizes to exactly the bytes it
+    /// did before the field existed, so every one sealed earlier still verifies.
+    /// The byte cost falls only on receipts making an unearned claim.
+    #[test]
+    fn a_real_closed_receipt_is_byte_identical_to_before_the_field() {
+        use proof_solvers::real_ladder;
+        let router = Router::new(real_ladder());
+        let mut cache = ProofCache::new();
+        let r = router.prove(
+            &ProofGoal::new("a | ~a", "prop", GoalKind::Trivial),
+            &mut cache,
+        );
+        assert!(r.proved && !r.closed_by_stub, "fixture must be closed by a real rung");
+
+        let wire = to_jcr1_wire(&r, "did:example:p");
+        assert!(
+            wire.as_object().unwrap().get("closed_by_stub").is_none(),
+            "the field must be absent, not false — an emitted 0 would change the bytes"
+        );
+
+        // Pin it at the level that actually matters: the canonical core is what
+        // gets signed and content-addressed, so compare bytes, not just the map.
+        let core = signed_core(&r, "did:example:p").unwrap();
+        let mut expected = to_jcr1_wire(&r, "did:example:p");
+        expected.as_object_mut().unwrap().remove("closed_by_stub");
+        assert_eq!(core, jcr1::signed_core_bytes(&expected).unwrap());
+    }
+
     #[test]
     fn unproved_goal_cannot_be_sealed() {
         // No solver in the reference ladder is unable to close General/Hard, so