Raise the editor floor to 1190x680, derived from the deck's declared width budget, and make row membership a property of the group

src/core/instrument/ui/knob_deck.h

@@ -23,8 +23,9 @@
 namespace reasampler::instrument::ui {
 
 // Fixed deck metrics, exposed so the shell and tests agree. The cell/knob/label sizes were
-// raised together for legibility at high pixel densities; the editor's floor width
-// (sample_bands) is what absorbs the wider cells, so the two move as a pair.
+// raised together for legibility at high pixel densities. The deck's cell metrics AND its
+// group/row composition BOTH drive sample_bands' kEditorMinWidth; none of the three may move
+// alone.
 inline constexpr int kDeckCellW = 60;         // one knob cell
 inline constexpr int kDeckCellH = 74;
 inline constexpr int kDeckKnobSize = 40;      // knob diameter inside the cell
@@ -46,6 +47,19 @@ inline constexpr int kDeckInnerDialSize = 20;
 inline constexpr int kDeckGroupH =
     kDeckGroupPadY + kDeckCaptionH + kDeckCaptionGap + kDeckCellH + kDeckGroupPadY;
 
+// --- The deck's width budget at the editor's floor ------------------------------------
+// DECLARATIONS of budget, not measurements: nothing here is computed from a descriptor, and a
+// group inventory that overruns one is what fails. sample_bands' kEditorMinWidth is derived
+// from the first two — kDeckRowBlockW + kDeckGroupGap + kDeckSpanningW + 2*kPad — and the
+// identity is asserted in test_deck_groups.cpp rather than coded, so the allocator keeps no
+// include edge to this header.
+inline constexpr int kDeckRowBlockW = 1020;  // the block both categorical rows justify inside
+inline constexpr int kDeckSpanningW = 142;   // the right-anchored spanning deck, outside the block
+// The hard ceiling the FLOOR may not exceed; the window itself still grows freely above it.
+// The gap between it and kEditorMinWidth is the whole width budget for the life of this
+// layout — see instrument-control-surface.md §1.6 before spending any of it.
+inline constexpr int kEditorCeilingWidth = 1280;
+
 // A two-segment compact toggle (always 2 segments — the Mono/Stereo grammar). id -1 = absent.
 struct DeckToggleDesc {
     int id = -1;        // shell control id returned by the hit-test; -1 = no toggle