Two compilers that walk a graph the same way walk it through one emitter (#85)

Refactoring round two: the particle and shader compilers share emitGraph.ts (cycle detection,
duplicate names, emit order) and keep only their rules. FontLibrary and TextureLibrary sit on
FileLibrary (base URL, loading/failed bookkeeping, listeners); SoundLibrary keeps its own
contract. The three Create*Command share ImportFileCommand, the three renames share
RenameCommand - class names stay. bandBounds() in framing.ts and portNameField() in
portSection.ts replace in-file clones, and three comments that told history now state the rule.

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

src/editor/framing.ts

@@ -68,16 +68,22 @@ export interface Framing {
   panY: number;
 }
 
+function bandBounds(band: Band): { minX: number; maxX: number; minY: number; maxY: number } {
+  return {
+    minX: Math.min(band.x1, band.x2),
+    maxX: Math.max(band.x1, band.x2),
+    minY: Math.min(band.y1, band.y2),
+    maxY: Math.max(band.y1, band.y2),
+  };
+}
+
 /**
  * Ids of every box the band overlaps. Nodes are large rectangles, so – unlike the scene view,
  * which tests an object's position – touching counts: a band drawn across a node that visibly
  * caught it would otherwise leave it out.
  */
 export function boxesInBand(boxes: readonly Box[], band: Band): string[] {
-  const minX = Math.min(band.x1, band.x2);
-  const maxX = Math.max(band.x1, band.x2);
-  const minY = Math.min(band.y1, band.y2);
-  const maxY = Math.max(band.y1, band.y2);
+  const { minX, maxX, minY, maxY } = bandBounds(band);
   return boxes
     .filter((b) => b.x <= maxX && b.x + b.w >= minX && b.y <= maxY && b.y + b.h >= minY)
     .map((b) => b.id);
@@ -90,10 +96,7 @@ export function boxesInBand(boxes: readonly Box[], band: Band): string[] {
  * Enclosing it is a deliberate gesture, and it is the one the eye reads as "this box, too".
  */
 export function boxesWithinBand(boxes: readonly Box[], band: Band): string[] {
-  const minX = Math.min(band.x1, band.x2);
-  const maxX = Math.max(band.x1, band.x2);
-  const minY = Math.min(band.y1, band.y2);
-  const maxY = Math.max(band.y1, band.y2);
+  const { minX, maxX, minY, maxY } = bandBounds(band);
   return boxes
     .filter((b) => b.x >= minX && b.x + b.w <= maxX && b.y >= minY && b.y + b.h <= maxY)
     .map((b) => b.id);