fix(abut): 벽체와 흉벽을 삽도대로 분리

- 벽체: 배면 −0.8 … 전면 1.6의 2400 블록을 기초 상면부터 교좌면 단차까지 (삽도의 회색 블록)
- 흉벽: 교좌면 단차 위에 얹음. 배면 단차부(−0.8 … −0.5)는 브라켓 상면(흉벽 상단 − 0.85)까지, 흉벽(−0.5 … 0)은 흉벽 상단까지
- 둘은 교좌면 단차에서 맞닿고 겹치지 않음. 배면 단차부는 흉벽 부재로 묶음
- 테스트 636건 통과, 타입 검사·빌드 통과. 브라우저 시각 확인은 미실시

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>

src/view/abut-scene.ts

@@ -133,29 +133,29 @@ export function buildAbutGroup(
   const footingTop = members.footingTopEl;
   const footingBottom = members.footingBottomEl;
 
-  // 벽체 (spec §4.3, 도면 type-1): the front part (t −0.5 … 1.6) stops at the 교좌면 step; the back ledge (t −0.8 … −0.5)
-  // rises to the 브라켓 상면 (흉벽 상단 − 0.85), where the 접속슬래브 sits. The two parts only touch the 흉벽 faces.
+  // 벽체 (spec §4.3, 삽도): the full 2400 block from the footing top up to the 교좌면 step (t −0.8 … 1.6).
   const parapetTopAt = (s: number) => members.parapetTopStartEl + ((members.parapetTopEndEl - members.parapetTopStartEl) * s) / L;
   const bracketAt = (s: number) => parapetTopAt(s) - members.shape.bracketHeightM;
   for (const seg of members.wallSegments) {
-    const front: [number, number][] = [
+    const block: [number, number][] = [
       [seg.sFrom, footingTop],
       [seg.sTo, footingTop],
       [seg.sTo, seg.seatEl],
       [seg.sFrom, seg.seatEl],
     ];
-    add('wall', prism(front, members.shape.wallFrontM - members.shape.parapetBackM, new THREE.Vector3(0, 0, members.shape.parapetBackM), ex, ey, ez), 0xb7c7d3);
-    const ledge: [number, number][] = [
-      [seg.sFrom, footingTop],
-      [seg.sTo, footingTop],
+    add('wall', prism(block, members.shape.wallFrontM - members.shape.wallBackM, new THREE.Vector3(0, 0, members.shape.wallBackM), ex, ey, ez), 0xb7c7d3);
+  }
+
+  // 흉벽 (삽도): sits on the 벽체 top, above the 교좌면 step. The back strip (t −0.8 … −0.5) rises to the 브라켓 상면 (흉벽 상단 − 0.85),
+  // where the 접속슬래브 sits; the 흉벽 (t −0.5 … 0) rises to the parapet top line. Both start at the 교좌면 step, so nothing overlaps the 벽체.
+  for (const seg of members.wallSegments) {
+    const backStrip: [number, number][] = [
+      [seg.sFrom, seg.seatEl],
+      [seg.sTo, seg.seatEl],
       [seg.sTo, bracketAt(seg.sTo)],
       [seg.sFrom, bracketAt(seg.sFrom)],
     ];
-    add('wall', prism(ledge, members.shape.parapetBackM - members.shape.wallBackM, new THREE.Vector3(0, 0, members.shape.wallBackM), ex, ey, ez), 0xb7c7d3);
-  }
-
-  // 흉벽: t −0.5 … 0, from the 교좌면 step (the top of the front wall) up to the parapet top line, so it never overlaps the wall.
-  for (const seg of members.wallSegments) {
+    add('parapet', prism(backStrip, members.shape.parapetBackM - members.shape.wallBackM, new THREE.Vector3(0, 0, members.shape.wallBackM), ex, ey, ez), 0x8898aa);
     const parapet: [number, number][] = [
       [seg.sFrom, seg.seatEl],
       [seg.sTo, seg.seatEl],

tests/abut-scene.test.ts

@@ -21,9 +21,9 @@ const group = buildAbutGroup(model, members, wings);
 const count = (name: string) => (group.getObjectByName(name) as THREE.Group | undefined)?.children.length ?? 0;
 
 describe('교대 A1 3D 장면 (AA3·AA3b·AA3c)', () => {
-  it('has the members: 5 wall segments (front + back ledge), 5 parapet parts, 1 footing, 18 piles, 2 wings, 4 haunches', () => {
-    expect(count('wall')).toBe(10); // 5 front parts + 5 back ledges (도면 type-1)
-    expect(count('parapet')).toBe(5); // one per 교좌면 step, from the step up
+  it('has the members: 5 wall blocks, 10 parapet parts (2 per step), 1 footing, 18 piles, 2 wings, 4 haunches', () => {
+    expect(count('wall')).toBe(5); // one 벽체 block per 교좌면 step (삽도)
+    expect(count('parapet')).toBe(10); // per step: back strip (흉벽 배면 단차) and the 흉벽 (삽도)
     expect(count('footing')).toBe(1);
     expect(count('piles')).toBe(18);
     expect(count('wings')).toBe(2);