deck: filter mod moves to FILTER ENV, cell runs centre in their reserves, two-segment toggles become single buttons, deck focuses its overlay

src/shell/instrument/editor_input.cpp

@@ -34,6 +34,14 @@ void ReaSamplerEditor::onMouseDown(int x, int y) {
     // Band order matters only where bands can overlap on a degenerate window; each branch
     // reports whether it consumed the click so the next band gets a clean shot.
     const FaceLayout fl = faceLayout(w, h);
+    // The overlay focus follows the deck (mouseDownDeck sets it), and clicking a control
+    // surface OUTSIDE the envelope decks clears it. The waveform band is deliberately not one
+    // of those surfaces: it IS the overlay, so editing what you selected must not deselect it.
+    if (drag_ == DragKind::kNone && contains(fl.bands.chrome, x, y) &&
+        overlayEnv_ != OverlayEnv::kNone) {
+        overlayEnv_ = OverlayEnv::kNone;
+        invalidate();  // the chrome branches below repaint only what THEY changed
+    }
     if (mouseDownChrome(fl, x, y)) return;
     if (selectedId_.empty()) return;  // empty state — chrome nav only
     if (mouseDownDeck(fl, x, y)) return;