Fix findUsages/undo/node-lookup bugs, split Viewport and Editor, share command and inspector helpers

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/ui/draw.ts

@@ -19,3 +19,36 @@ export function drawControlBox(g: Graphics, w: number, h: number, options: Contr
   g.roundRect(x, y, w, h, radius).fill(fill);
   g.roundRect(x + 0.5, y + 0.5, w - 1, h - 1, radius).stroke({ width: 1, color: border });
 }
+
+export interface GridOptions {
+  /** Where the origin of the drawn space sits on screen, in the same pixels as `w`/`h`. */
+  originX: number;
+  originY: number;
+  /** Spacing in screen pixels (world/graph step times zoom). */
+  step: number;
+  w: number;
+  h: number;
+  alpha: number;
+  /** Alpha of the two lines through the origin; omitted = no axes (the graph has no origin to show). */
+  axisAlpha?: number;
+}
+
+/**
+ * The background grid of the scene view and the graph editor. Drawn in white at a low alpha
+ * rather than in a fixed colour, so it reads on whatever background the scene sets.
+ * `g` is cleared by the caller, which also decides when the step is too dense to be useful.
+ */
+export function drawGrid(g: Graphics, options: GridOptions): void {
+  const { originX, originY, step, w, h, alpha, axisAlpha } = options;
+  const startX = ((originX % step) + step) % step;
+  const startY = ((originY % step) + step) % step;
+  for (let x = startX; x < w; x += step) g.moveTo(x, 0).lineTo(x, h);
+  for (let y = startY; y < h; y += step) g.moveTo(0, y).lineTo(w, y);
+  g.stroke({ width: 1, color: GRID_COLOR, alpha });
+  if (axisAlpha === undefined) return;
+  const axis = { width: 1, color: GRID_COLOR, alpha: axisAlpha };
+  if (originX >= 0 && originX <= w) g.moveTo(originX, 0).lineTo(originX, h).stroke(axis);
+  if (originY >= 0 && originY <= h) g.moveTo(0, originY).lineTo(w, originY).stroke(axis);
+}
+
+const GRID_COLOR = 0xffffff;