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/editor_input.cpp

@@ -105,7 +105,7 @@ void ReaSamplerEditor::onMouseUp(int x, int y) {
         return;
     }
     // A live control already reached the voices during the drag; its release commits the
-    // final value the same way — no bridge read, no WAV re-decode, no snapshot rebuild.
+    // final value through the same tier.
     if (dragCommitsLive(kind, paramId)) {
         commitLive();
         invalidate();