One taper, one modifier law: extract param_taper, raise the stage ceiling to 10 s, and make the AHDSR schematic axis the taper itself

src/shell/instrument/editor_input_deck.cpp

@@ -6,6 +6,7 @@
 
 #ifdef _WIN32
 
+#include "core/instrument/ui/deck_values.h"     // snapDeckParamNorm (Shift's whole-unit table)
 #include "core/instrument/ui/knob_deck.h"       // hitTestDeck / layoutDeck
 #include "core/instrument/ui/param_slider.h"    // knobDragValue (grab-anchored drag)
 #include "shell/instrument/editor_internal.h"
@@ -97,6 +98,7 @@ bool ReaSamplerEditor::mouseDownDeck(const FaceLayout& fl, int x, int y) {
         dragParamId_ = inner ? static_cast<int>(curve) : hit.id;
         dragInnerCellId_ = inner ? hit.id : -1;
         dragKnobStartValue_ = deckControlNorm(dragParamId_);
+        dragMods_ = dragModifiers();
         // Processor-side knobs (voice count / master gain) are transient live writes with no
         // parameter-set mutation, so they need no rollback snapshot.
         dragStartParams_ = params_;
@@ -150,7 +152,20 @@ void ReaSamplerEditor::dragDeck(int x, int y) {
     // value at grab (up = increase), so the value tracks relative motion and never jumps on
     // grab. Live feedback; parameter-set commits land on WM_LBUTTONUP.
     (void)x;
-    applyDeckKnob(dragParamId_, knobDragValue(dragKnobStartValue_, y - dragStartY_));
+    const DragModifiers mods = dragModifiers();
+    if (mods != dragMods_) {
+        // Re-anchor (see dragMods_). Reading the anchor back off the control also means a Shift
+        // RELEASE re-anchors from the SNAPPED value, so the knob does not spring back.
+        dragKnobStartValue_ = deckControlNorm(dragParamId_);
+        dragStartY_ = y;
+        dragMods_ = mods;
+    }
+    double norm = knobDragValue(dragKnobStartValue_, y - dragStartY_, mods);
+    // The preview-velocity sentinel (-2) and the discrete controls have no whole unit to snap to.
+    if (mods.shift && dragParamId_ >= 0) {
+        norm = snapDeckParamNorm(static_cast<DeckParam>(dragParamId_), norm);
+    }
+    applyDeckKnob(dragParamId_, norm);
     // A live control is delivered on every move, not only on release — that is the whole
     // point: the note already sounding tracks the hand on the knob.
     if (dragCommitsLive(DragKind::kDeckKnob, dragParamId_)) commitLive();