fix(abut): 날개벽을 삽도대로 흉벽·벽체 배면에 맞닿게 나눔

- 날개벽을 상·하 두 부분으로 나눔. 브라켓 상면 위는 흉벽 배면(−0.5)에, 아래는 벽체 배면(−0.8)에 맞닿음 (삽도 A-A와 평면)
- 브라켓 상면이 s 방향으로 기울어 있으므로, 두께 0.45 m 안에서 가장 높은 브라켓 상면을 기준으로 자름
- 헌치는 기존 위치 유지: 위 헌치는 흉벽 배면 모서리, 아래 헌치는 벽체 배면 모서리
- 테스트 갱신: 날개벽 상부·하부 경계, 날개벽 개수 4. 전체 638건 통과, 타입 검사·빌드 통과. 브라우저 시각 확인은 미실시

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

src/view/abut-scene.ts

@@ -79,6 +79,23 @@ function toAxis(model: AbutModel, p: AbutPoint): { s: number; t: number } {
   return { s: d.e * model.u.e + d.n * model.u.n, t: d.e * front.e + d.n * front.n };
 }
 
+/** Keeps the part of a 2-D profile where g(x, y) ≥ 0 (Sutherland–Hodgman; g is linear, so the cut is a straight line). */
+function clipByLine(poly: [number, number][], g: (x: number, y: number) => number): [number, number][] {
+  const out: [number, number][] = [];
+  for (let i = 0; i < poly.length; i++) {
+    const p = poly[i];
+    const q = poly[(i + 1) % poly.length];
+    const gp = g(p[0], p[1]);
+    const gq = g(q[0], q[1]);
+    if (gp >= 0) out.push(p);
+    if (gp * gq < 0) {
+      const f = gp / (gp - gq);
+      out.push([p[0] + (q[0] - p[0]) * f, p[1] + (q[1] - p[1]) * f]);
+    }
+  }
+  return out;
+}
+
 /** Keeps the part of a 2-D profile with x ≥ x0 (Sutherland–Hodgman against one line). */
 function clipBelowX(poly: [number, number][], x0: number): [number, number][] {
   const out: [number, number][] = [];
@@ -255,9 +272,18 @@ export function buildAbutGroup(
       ...[...wing.bottomLine].reverse().map((p) => [p.dM, p.el] as [number, number]),
     ];
     const ax = new THREE.Vector3(dir.ws, 0, dir.wt);
-    // The wing starts behind the 벽체 back face (t = 벽체 배면 −0.8): the part in front of it lies inside the 벽체 and 흉벽, so it is cut off.
-    const geom = prism(clipBelowX(profile, members.shape.wallBackM / dir.wt), 0.45, new THREE.Vector3(sEnd, 0, 0), ax, ey, new THREE.Vector3(a, 0, 0));
-    add('wings', geom, 0xc9a77c);
+    // 삽도 (A-A, 평면): above the 브라켓 상면 the wing meets the 흉벽 back face (t = −0.5); below it, the wing meets the 벽체 back face (t = −0.8).
+    // The part in front of those faces lies inside the 벽체 or 흉벽, so it is cut off. The bracket falls along s, so the cut follows it.
+    // The wing is 0.45 thick along s, so its footprint spans two s values at each dM; the cut uses the end where the 브라켓 is highest.
+    const slopeS = (members.parapetTopEndEl - members.parapetTopStartEl) / L;
+    const highEnd = slopeS < 0 ? Math.min(0, a * WING_THICKNESS_M) : Math.max(0, a * WING_THICKNESS_M);
+    const bracketAtDm = (dM: number) => members.parapetTopStartEl + slopeS * (sEnd + dir.ws * dM + highEnd) - members.shape.bracketHeightM;
+    const above = clipByLine(profile, (x, y) => y - bracketAtDm(x));
+    const below = clipByLine(profile, (x, y) => bracketAtDm(x) - y);
+    const upper = prism(clipBelowX(above, members.shape.parapetBackM / dir.wt), WING_THICKNESS_M, new THREE.Vector3(sEnd, 0, 0), ax, ey, new THREE.Vector3(a, 0, 0));
+    const lower = prism(clipBelowX(below, members.shape.wallBackM / dir.wt), WING_THICKNESS_M, new THREE.Vector3(sEnd, 0, 0), ax, ey, new THREE.Vector3(a, 0, 0));
+    add('wings', upper, 0xc9a77c);
+    add('wings', lower, 0xc9a77c);
     for (const h of wing.haunches) {
       const shape: [number, number][] = h.corners.map((c) => {
         const p = toAxis(model, c);