Preserve's period detection: probes are placed by position, and a sustain loop is the span analysed

src/core/instrument/map/sample_map.cpp

@@ -329,9 +329,14 @@ SampleData buildSampleData(const ResolvedCapture& resolved, DecodedPcm decoded)
     data.play = resolvePlay(resolved.play, data.sampleRate);
     // The one place Preserve's source period is computed: the load, off the audio thread.
     // Channel 0 only — a stereo pair's two channels share a fundamental, and the splice
-    // schedule is linked across them anyway.
+    // schedule is linked across them anyway. The span is the sustain loop where one is long
+    // enough (periodAnalysisSpan owns that rule) — every input to it commits through a full
+    // reload, so the cache is re-derived whenever the span it was chosen from moves.
+    const instrument::engine::AnalysisSpan span = instrument::engine::periodAnalysisSpan(
+        data.frames.size(), data.loop.start, data.loop.end, data.loop.hasLoop, data.sampleRate);
     data.sourcePeriodFrames =
-        instrument::engine::detectPeriod(data.frames, data.sampleRate).frames;
+        instrument::engine::detectPeriod(data.frames, data.sampleRate, span.from, span.count)
+            .frames;
     return data;
 }