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

src/core/instrument/ui/deck_groups.cpp

@@ -119,9 +119,40 @@ bool isLiveDeckParam(DeckParam id) {
         case DeckParam::kFilterEnvSustain:
         case DeckParam::kFilterEnvRelease:
             return true;
-        default:
+        // Listed rather than defaulted so a newly added control is a COMPILE error here (the
+        // -Wswitch gate is GCC/Clang; MSVC's C4062 is off at this project's warning level)
+        // instead of silently defaulting to non-live. Reasons live in the header.
+        case DeckParam::kPlayMode:
+        case DeckParam::kPitchEngine:
+        case DeckParam::kTrigLength:
+        case DeckParam::kTrigFadeIn:
+        case DeckParam::kTrigFadeOut:
+        case DeckParam::kPitchEnvEnable:
+        case DeckParam::kKeyTrack:
+        case DeckParam::kFilterEnable:
+        case DeckParam::kFilterVel:
+        case DeckParam::kFilterLaw:
+        case DeckParam::kVoiceCount:
+        case DeckParam::kVoiceMode:
+        case DeckParam::kMonoTrigger:
+        case DeckParam::kMasterGain:
+        case DeckParam::kCount:  // not a control
             return false;
     }
+    return false;  // unreachable for a valid enumerator; silences a warning.
+}
+
+bool liveCommitFor(LiveDragKind kind, int paramId, PlayMode playMode) {
+    switch (kind) {
+        case LiveDragKind::kDeckKnob:
+            return paramId >= 0 && paramId < static_cast<int>(DeckParam::kCount) &&
+                   isLiveDeckParam(static_cast<DeckParam>(paramId));
+        case LiveDragKind::kEnvNode:
+            return playMode == PlayMode::Gate;
+        case LiveDragKind::kOther:
+            return false;
+    }
+    return false;
 }
 
 }  // namespace reasampler::instrument::ui