fix: expose physical aliasing and delayed arrivals

tests/unit/builder.test.js

@@ -5,6 +5,7 @@ import {
   enableSourceTrajectory,
   createSceneId,
   createSource,
+  describeSignal,
   insertTrajectoryKeyframe,
   matchAssetDescriptor,
   prepareSceneForEditing,
@@ -49,6 +50,29 @@ test("Builder model이 schema-safe하고 안정적인 source/asset id를 만든
   assert(/^[a-z0-9][a-z0-9._-]*$/.test(createSceneId()), "generated scene id is schema-safe");
 });
 
+test("Builder tone summary exposes the ideal ADC alias above Nyquist", () => {
+  assertEqual(
+    describeSignal({ type: "tone", frequency: 5_000 }, 8_000),
+    "5000 Hz tone → ADC 3000 Hz alias",
+    "above-Nyquist source summary",
+  );
+  assertEqual(
+    describeSignal({ type: "tone", frequency: 1_000 }, 8_000),
+    "1000 Hz tone",
+    "baseband source summary",
+  );
+  assertEqual(
+    describeSignal({ type: "tone", frequency: 8_000 }, 8_000),
+    "8000 Hz tone → ADC 0 Hz alias · DC phase-degenerate edge",
+    "aliased exact-DC source summary",
+  );
+  assertEqual(
+    describeSignal({ type: "tone", frequency: 12_000 }, 8_000),
+    "12000 Hz tone → ADC 4000 Hz alias · Nyquist phase-degenerate edge",
+    "aliased exact-Nyquist source summary",
+  );
+});
+
 test("Builder가 이동 경로를 순서대로 편집하고 fallback position을 첫 점에 맞춘다", () => {
   const source = { position: [0.5, 0.1, 2] };
   const trajectory = enableSourceTrajectory(source, 2, { xMin: -0.6, xMax: 0.6, yMin: -0.45, yMax: 0.45 });