UX second pass: icon-only header, pane-toggle cue, schema columns, facet cleanup

src/app/components/ChartBuilderModal.tsx

@@ -620,24 +620,13 @@ function MarksCard() {
   );
 }
 
-/** A reserved, non-interactive shelf slot for faceting (small multiples) — Phase 4.
- *  Shown so the layout telegraphs where row/column faceting will live. */
-// TODO: the "later" tag is internal roadmap language shown to users — hide the
-// affordance until faceting ships, or reword for users (docs/ux-second-pass.md).
-function FacetSlot({ kind }: { kind: 'column' | 'row' }) {
-  return (
-    <div className={styles.facetSlot} title="Faceting → small multiples (coming later)">
-      <span>+ {kind} facet</span>
-      <span className={styles.facetTag}>later</span>
-    </div>
-  );
-}
-
 /**
  * The on-chart **Columns** (X) and **Rows** (Y) shelves stacked above the preview,
  * Tableau-style — position is a property of the chart, so its controls sit on the
- * chart. Each shelf holds the axis slot plus a reserved faceting placeholder. A Swap
- * X/Y action flips the two axes.
+ * chart. A Swap X/Y action flips the two axes. The slot rows are shelf-shaped so
+ * Phase 4 faceting can add a second slot per shelf without a layout change, but
+ * no placeholder ships before the feature does (an affordance promising unbuilt
+ * functionality is a promise, not a feature — NN/g #2/#8).
  */
 function OnChartShelves() {
   const swapXY = useChartBuilderStore((s) => s.swapXY);
@@ -653,14 +642,12 @@ function OnChartShelves() {
         <span className={styles.shelfName}>Columns</span>
         <div className={styles.shelfSlots}>
           <ChannelSlot channel="x" hint="Add a field for the X axis" />
-          <FacetSlot kind="column" />
         </div>
       </div>
       <div className={styles.shelfStrip}>
         <span className={styles.shelfName}>Rows</span>
         <div className={styles.shelfSlots}>
           <ChannelSlot channel="y" hint="Add a field for the Y axis" />
-          <FacetSlot kind="row" />
         </div>
       </div>
     </div>