Period detection: silence is not dissent but an absent period is — the agreement denominator is the probes that carried signal

tests/test_sample_map.cpp

@@ -957,12 +957,14 @@ static void testBuildSampleDataDetectsOverTheSustainLoopNotTheWholeSource() {
     CHECK(std::fabs(sd.sourcePeriodFrames - loopPeriod) < 2.0);
 
     // A loop too short to host the full search band falls back to the whole source rather than
-    // to none — here that whole source has no one period, so the answer is the bare one above.
+    // to none — here that whole source has no one period, so the answer is none. Asserted
+    // against the literal, not against `bare`: the two agreeing would also hold if both
+    // regressed together, which is no evidence that the fallback ran.
     InstrumentParams shortLoop;
     shortLoop.loopOverride = SampleLoop{true, 118000, static_cast<std::int64_t>(frames)};
     const SampleData shortSd = buildSampleData(resolveCapture(ref("b/a.wav", 60), shortLoop),
                                                DecodedPcm{pcm, rate, {}});
-    CHECK(shortSd.sourcePeriodFrames == bare.sourcePeriodFrames);
+    CHECK(shortSd.sourcePeriodFrames == 0.0);
 }
 
 static void testBuildSampleDataCarriesTheVelocityCurve() {