fix: close round-2 review findings — Critical silent-note bug plus majors/minors

Fixes the 2-point spline-EG early-free bug causing silent fade-ins, the pitch/filter enable-toggle Trigger-forcing hole, the contour-node/marker pixel shadow, missing deck-residue test coverage, and stale comments in knob_deck and spline_edit.

src/shell/instrument/editor_input_waveform.cpp

@@ -31,11 +31,6 @@ bool ReaSamplerEditor::mouseDownWaveform(const FaceLayout& fl, int x, int y) {
     if (frames <= 0) return false;
     const OverlayArea overlay = waveformOverlayArea(fl.bands.waveform);
 
-    // A drawn EG's contour is evaluated below, AFTER the markers: pointAtPixel's pick radius
-    // has no box check of its own, so a coincident contour node would otherwise shadow a
-    // marker's own dedicated grab rect (the loop-crossfade tab most sharply, since it is the
-    // ONLY affordance at zero crossfade) — marker reachability wins on any pixel overlap. The
-    // staged envelope-node pass just below is unaffected (its own, longer-standing ordering).
     const DeckEnableState gates = deckEnableState();
     const bool splineLive = overlayIsSpline() && overlayEnvEnabled(overlayEnv_, gates);
     const SplineGesture gesture = (GetKeyState(VK_CONTROL) & 0x8000) != 0
@@ -64,6 +59,17 @@ bool ReaSamplerEditor::mouseDownWaveform(const FaceLayout& fl, int x, int y) {
             return true;  // node moves once the cursor drags
         }
     }
+    // An existing contour node's grab/toggle/delete runs BEFORE the markers — mirroring
+    // markerHandleRect's tab-vs-column split (below): a coincident pixel (the default contour
+    // endpoint sits at the same x as the default start marker) is resolved by asking the
+    // NARROWER target first. pointAtPixel's pick radius is a small box around the node's own
+    // (x, y), not a full-height column, so this claims only genuine node hits — the marker's
+    // column stays grabbable at every other y along the same x. Never add here (kAdd is only
+    // tried once the markers have also passed on the click, below).
+    if (splineLive && splineOverlayClick(overlay, x, y, gesture, /*addOnEmptySpace=*/false)) {
+        return true;
+    }
+
     const SetupMarkers m = pickedMarkers(frames);
     // The crossfade handle first, and only when there IS a loop to fade: at a zero fade it
     // sits exactly on the loop start, so it can only stay reachable by owning the top strip
@@ -82,11 +88,6 @@ bool ReaSamplerEditor::mouseDownWaveform(const FaceLayout& fl, int x, int y) {
         beginMarkerDrag(static_cast<WaveMarker>(hit), m, frames, x);
         return true;
     }
-    // No marker wanted the click: a drawn EG's own node grab/toggle (never add — empty space is
-    // tried last, below).
-    if (splineLive && splineOverlayClick(overlay, x, y, gesture, /*addOnEmptySpace=*/false)) {
-        return true;
-    }
     // Nothing else wanted the click: now the drawn contour may take the empty space.
     if (splineLive) return splineOverlayClick(overlay, x, y, gesture, /*addOnEmptySpace=*/true);
     return false;