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_session.cpp

@@ -144,13 +144,14 @@ void ReaSamplerEditor::commitLive() {
 }
 
 bool ReaSamplerEditor::dragCommitsLive(DragKind kind, int paramId) const {
-    if (kind == DragKind::kDeckKnob) {
-        // Negative ids are the processor-side sentinels (preview velocity), not parameter-set
-        // controls, so they never reach the enum.
-        return paramId >= 0 &&
-               instrument::ui::isLiveDeckParam(static_cast<ParamControl>(paramId));
-    }
-    return kind == DragKind::kEnvNode && params_.play.playMode == PlayMode::Gate;
+    // The decision itself is the pure liveCommitFor's; this is only the shell's drag-kind
+    // vocabulary mapped onto it, so the routing is pinned by deck_groups' tests rather than
+    // by inspection of this file.
+    using instrument::ui::LiveDragKind;
+    const LiveDragKind k = kind == DragKind::kDeckKnob ? LiveDragKind::kDeckKnob
+                         : kind == DragKind::kEnvNode  ? LiveDragKind::kEnvNode
+                                                       : LiveDragKind::kOther;
+    return instrument::ui::liveCommitFor(k, paramId, params_.play.playMode);
 }
 
 void ReaSamplerEditor::loadSelection(const std::string& id) {