instrument: snap live params onto a fresh voice, roll a live drag back on capture loss, serialize the seqlock's two writers

src/shell/instrument/reasampler_processor.h

@@ -154,11 +154,10 @@ public:
 
     // Republishes the live-parameter block from the stored parameter set, resolved against the
     // rate the loaded capture was built at so an unmoved value folds to exactly the frames the
-    // voices already latched. THE tier-3 commit: no bridge read, no WAV re-decode, no engine
-    // rebuild, no snapshot swap — the sounding note follows the knob. Persistence is
-    // unaffected: getState still serializes params_, so callers pair this with
-    // setInstrumentParams exactly as they paired it with reloadInstrument. No-op before
-    // anything has been decoded (the next reload bakes and publishes). UI thread.
+    // voices already latched. THE tier-3 commit (the three tiers are listed in this
+    // directory's CLAUDE.md). Callers pair this with setInstrumentParams exactly as they
+    // paired it with reloadInstrument. No-op before anything has been decoded (the next reload
+    // bakes and publishes). UI thread; serialized against reloadInstrument's own publish.
     void publishLiveParams();
 
     // Per-instance channel mode (mono | stereo), guarded by channelModeMutex_, never read
@@ -243,6 +242,13 @@ private:
     // The rate the loaded capture was decoded/built at, so a live republish resolves the
     // stored wall-clock seconds to exactly the frames the built SampleData carries. 0 = nothing
     // built yet.
+    //
+    // ONE BLOCK, ONE RATE: this is stamped by whichever capture built last, and a reload
+    // publishes the new block before installing the new instrument. Swapping to a capture at a
+    // different rate therefore hands drain voices still ringing from the old-rate capture
+    // envelope frame counts resolved at the NEW rate (~8.8% timing shift on a 48k->44.1k swap).
+    // Unavoidable while one block sits above every snapshot, and it touches a release tail
+    // only.
     std::atomic<int> builtSampleRate_{0};
 
     // --- The audio-thread handoff (drain slot) ---