Fix deck-UI review findings: right-anchor MASTER's meter column, correct stale/overclaiming comments, split test_deck_groups.cpp on its commit-tier/overlay seam, and pin two width-ceiling assertions.

src/core/instrument/ui/knob_deck.cpp

@@ -8,8 +8,8 @@ namespace reasampler::instrument::ui {
 
 namespace {
 
-// The knob-row width of a group: cells side by side (no inter-cell gap — the 48px cell
-// already carries its own breathing room around the 28px knob), plus the optional row
+// The knob-row width of a group: cells side by side (no inter-cell gap — the 60px cell
+// already carries its own breathing room around the 40px knob), plus the optional row
 // toggle after a kDeckToggleGap. A spanning group's cells stack, so its knob row is one
 // cell wide plus whatever readout column sits beside it.
 int knobRowWidth(const DeckGroupDesc& g) {
@@ -109,8 +109,10 @@ DeckGroupLayout layoutGroup(const DeckGroupDesc& g, const Rect& box) {
             slotTop += kDeckGroupH + kDeckRowGap;
         }
         if (g.column.id >= 0) {
-            // ONE rect spanning every slot, not a readout per row.
-            const int colX = innerLeft + (g.cellIds.empty() ? 0 : kDeckCellW + kDeckColumnGap);
+            // ONE rect spanning every slot, not a readout per row. Right-anchored off
+            // innerRight rather than measured past the cell slot, so a wider caption
+            // reserve on this group can never detach the column from the padding.
+            const int colX = innerRight - g.column.width;
             out.column = DeckColumnLayout{
                 g.column.id, Rect::ltrb(colX, cellTop, colX + g.column.width,
                                         box.bottom() - kDeckGroupPadY)};
@@ -156,7 +158,7 @@ std::vector<int> justifyGutters(int count, int total, int blockW) {
     const int slack = blockW - total;
     if (slack < gutters * kDeckGroupGap) {
         // The block cannot hold the row: minimum gutters, and the row overruns to the right
-        // rather than wrapping. Unreachable in the editor — see layoutDeck's header note.
+        // rather than wrapping — see layoutDeck's header note for when this degrade applies.
         return std::vector<int>(static_cast<std::size_t>(gutters), kDeckGroupGap);
     }
     const int base = slack / gutters;