Gamma-W1-T7: gate PSOLA's two untested wires, fix the cadence test's contradictory rationale, add a vacuity guard

tests/test_sample_map.cpp

@@ -909,6 +909,23 @@ static void testBuildSampleDataEmptyPcmIsUnplayable() {
     CHECK(sd.frames.empty());
 }
 
+// Major-1 remediation: buildSampleData (sample_map.cpp:333-334) is the ONE call site wiring
+// load-time detection to SampleData; detectPeriod's own unit coverage (test_period_detect.cpp)
+// never exercises this call, so a deleted wire passed the gated suite unnoticed. Goes through
+// the real build, not a direct detectPeriod call.
+static void testBuildSampleDataDetectsThirtyHertzSourcePeriod() {
+    const int rate = 44100;
+    const std::size_t frames = 30000;
+    std::vector<AudioSample> pcm(frames);
+    for (std::size_t i = 0; i < frames; ++i) {
+        pcm[i] = static_cast<float>(
+            std::sin(2.0 * 3.14159265358979323846 * 30.0 * static_cast<double>(i) / rate));
+    }
+    const SampleData sd = buildSampleData(resolveCapture(ref("b/a.wav", 60), InstrumentParams{}),
+                                          DecodedPcm{pcm, rate, {}});
+    CHECK(std::fabs(sd.sourcePeriodFrames - 1470.0) < 2.0);  // 44100 / 30 Hz
+}
+
 static void testBuildSampleDataCarriesTheVelocityCurve() {
     InstrumentParams p;
     p.velocityCurve = VelocityCurve::linear();
@@ -976,6 +993,7 @@ int main() {
     testBuildSampleDataDropsMismatchedSecondChannel();
     testBuildSampleDataEmptyPcmIsUnplayable();
     testBuildSampleDataCarriesTheVelocityCurve();
+    testBuildSampleDataDetectsThirtyHertzSourcePeriod();
 
     if (g_fail == 0) std::printf("sample_map: all tests passed\n");
     return g_fail != 0;