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

tests/test_sampler_core.cpp

@@ -2991,6 +2991,25 @@ static void testPreserveUnityRateIsBitIdenticalToTheShippedRead() {
     }
 }
 
+// --- The load->voice wire is load-bearing: Voice::start (voice.cpp:248-249) is the only place
+//     a detected period reaches the shifter. Assert the two SampleDatas actually render
+//     differently rather than only that setSourcePeriod is callable — dropping either of the
+//     wire's two lines left this whole gated suite green before this test existed.
+static void testSourcePeriodChangesTheRenderedStream() {
+    const std::int64_t w = 2205;   // the product window at 44.1k
+    const std::size_t n = 6000;
+    SampleData off = stretchProbeSample(20000, false);
+    SampleData on = off;
+    // 30 Hz @ 44.1k: periodAlignedJump takes ONE whole period (1470), which cannot fit twice
+    // inside the shifter's reachable jump bound — a different splice geometry from the fixed
+    // 2205-frame window, so a wire failure here cannot pass by coincidence.
+    on.sourcePeriodFrames = 1470.0;
+    std::vector<AudioSample> lOff(n), lOn(n), rUnused;
+    renderVoice(off, /*note=*/67, /*rate=*/1.0, w, false, lOff, rUnused);  // +7 st: real splices
+    renderVoice(on, 67, 1.0, w, false, lOn, rUnused);
+    CHECK(hashStream(lOff) != hashStream(lOn));
+}
+
 // --- Rate changes DURATION only; the transposition alone sets pitch. ---
 static void testPreserveStretchChangesDurationNotPitch() {
     // Gate, no loop: the voice's life is exactly how long the source lasts, so the frame at
@@ -3419,6 +3438,7 @@ int main() {
 
     // The Preserve read path's stretch generalization.
     testPreserveUnityRateIsBitIdenticalToTheShippedRead();
+    testSourcePeriodChangesTheRenderedStream();
     testPreserveStretchChangesDurationNotPitch();
     testPreserveStretchSpeaksOnFrameZeroAtEveryRate();
     testPreserveStretchLoopsTheSourceSpan();