diff --git a/crates/aura-engine/src/construction.rs b/crates/aura-engine/src/construction.rs
index f601e9a..ffa93e7 100644
--- a/crates/aura-engine/src/construction.rs
+++ b/crates/aura-engine/src/construction.rs
@@ -659,6 +659,51 @@ mod tests {
         assert_eq!(names, ["length"]);
     }
 
+    /// #261 — the Frankfurt `Session` preset is reachable from a blueprint. The
+    /// property this pins: a data-only op-script (a blueprint) that names the
+    /// preset's closed-roster type-id resolves it through `std_vocabulary`,
+    /// carries its one scalar `period_minutes` knob and the `bars_since_open:
+    /// i64` session-index output, wires its `trigger` input through the ordinary
+    /// edge convention, and builds to a finished `Composite`. Reachability is the
+    /// whole ask — the node's tz-aware/DST session SEMANTICS are already pinned
+    /// in `aura-std/src/session.rs` and are not re-pinned here. Today the preset
+    /// id is absent from the roster (the base `Session` builder takes structural
+    /// construction args, so the zero-arg macro cannot host it), so the lookup
+    /// returns `None` and the op-script's `Add` would fail `UnknownNodeType`.
+    #[test]
+    fn session_frankfurt_preset_is_reachable_from_a_blueprint() {
+        // (a) the preset resolves through the closed roster as the Session preset
+        //     — its one scalar knob and its i64 session-index output, not some
+        //     other node parked under the id.
+        let preset = std_vocabulary("SessionFrankfurt")
+            .expect("the Frankfurt Session preset is in the std vocabulary roster");
+        assert_eq!(preset.label(), "SessionFrankfurt");
+        let schema = preset.schema();
+        assert_eq!(schema.params.len(), 1, "exactly one scalar knob");
+        assert_eq!(schema.params[0].name, "period_minutes");
+        assert_eq!(schema.params[0].kind, ScalarKind::I64);
+        assert_eq!(schema.inputs.len(), 1);
+        assert_eq!(schema.inputs[0].name, "trigger");
+        assert_eq!(schema.output[0].name, "bars_since_open");
+        assert_eq!(schema.output[0].kind, ScalarKind::I64);
+
+        // (b) an op-script naming that id builds: a bound trigger source feeds the
+        //     preset's `trigger`, its `period_minutes` knob binds, and the i64 bar
+        //     index exposes — a data-only blueprint reaching the session stream.
+        let ops = vec![
+            Op::Source { role: "trigger".into(), kind: ScalarKind::F64 },
+            Op::Add {
+                type_id: "SessionFrankfurt".into(),
+                as_name: Some("session".into()),
+                bind: vec![("period_minutes".into(), Scalar::i64(15))],
+            },
+            Op::Feed { role: "trigger".into(), into: vec!["session.trigger".into()] },
+            Op::Expose { from: "session.bars_since_open".into(), as_name: "bars".into() },
+        ];
+        super::replay("session_blueprint", ops, &std_vocabulary)
+            .expect("the preset resolves, wires and builds through an op-script");
+    }
+
     /// Eager refusals: unknown member param (a member bound at `Add` has left the
     /// open schema), kind mismatch across members, a doubly-ganged member, a
     /// single-member gang, and an unknown node identifier.