diff --git a/crates/epiphany-ops/src/reduce.rs b/crates/epiphany-ops/src/reduce.rs
index 9213111..bc63db5 100644
--- a/crates/epiphany-ops/src/reduce.rs
+++ b/crates/epiphany-ops/src/reduce.rs
@@ -13129,9 +13129,20 @@ mod tests {
 
     /// (t9) Regression guard: the from-empty spine still reaches a note, now
     /// with a `SetTuningContext` authored alongside it — genesis tranche G2b
-    /// does not disturb the spine G1 established. Mutation is t2's (the
-    /// `schema_major` arm), which this test does not re-verify on its own;
-    /// its job is to prove the spine and the new op coexist cleanly.
+    /// does not disturb the spine G1 established.
+    ///
+    /// **Mutation:** replace this kind's dispatch arm with
+    /// `OperationKind::SetTuningContext(_) => OperationEffect::Applied`, which
+    /// bypasses tuning reduction without making the match non-exhaustive. The
+    /// spine ops stay applied and the note stays reachable; the *authored
+    /// tuning-context* assertions fail (the seeded default survives instead of
+    /// the authored value).
+    ///
+    /// This comment previously claimed the mutation was t2's (the
+    /// `schema_major` arm). The sweep disproved that: t9 stayed **green**
+    /// under it, because the spine reaches a note whatever the block stamps.
+    /// A mutation borrowed from another test signs nothing unless it is
+    /// observed to kill *this* one.
     #[test]
     fn from_empty_spine_reaches_a_note_with_a_tuning_context_authored() {
         let spine = genesis_spine_envelopes();
diff --git a/spec/CONTRACT_GENESIS_G2B_TUNING.md b/spec/CONTRACT_GENESIS_G2B_TUNING.md
index fab1c76..b5f8bd3 100644
--- a/spec/CONTRACT_GENESIS_G2B_TUNING.md
+++ b/spec/CONTRACT_GENESIS_G2B_TUNING.md
@@ -334,7 +334,7 @@ plan.
 | t6 | Undo restores the previous five-field value | Restore the default instead of the predecessor; must fail |
 | t7 | Undo of the **first** authoring restores the **seeded base** settings, and does so identically whether the seed was the default or a non-default value — with `accidental_extensions` untouched throughout | Skip `seed()` on the tuning chain during base ingest, so the first undo yields `NotWritten` instead of `Restore(Base)`; must fail. **Assert the two cases are indistinguishable**, not that they differ |
 | t8 | Kind 34 carries **epoch 10** and a block containing it stamps minor 10 | Assign epoch 9; must fail |
-| t9 | The from-empty spine still reaches a note, now with a tuning context authored | — regression guard; mutation is t2's |
+| t9 | The from-empty spine still reaches a note, now with a tuning context authored | Replace the dispatch arm with `OperationKind::SetTuningContext(_) => OperationEffect::Applied` (`reduce.rs`), bypassing tuning reduction while keeping the match exhaustive; must fail on the **authored tuning-context** assertions while the spine ops stay applied and the note stays reachable. **Corrected 2026-07-29:** this row previously said "mutation is t2's", which the sweep disproved — t9 stayed green under t2's `schema_major` change, because the spine reaches a note regardless of stamping. A shared mutation that does not kill the test signs nothing |
 | t10 | The accept-set prose no longer claims no payload embeds the tuning context | Grep-assert the stale sentence is absent; restore it to see the test fail |
 
 ---