fix(shape): 받침 번호가 축 반대 방향이어도 계단을 g 순서로 만든다

전·후열 받침 수가 같으면 받침을 번호 순서로 두어, 번호가 IP1 → IP3 반대로 매겨진 교각(산외교 P9: ① g 12.1,
③ g 1.3)에서 계단 경계가 거꾸로(9.42 → 4.02) 놓이고 코핑 상면이 틀렸다. 받침을 늘 g 순서로 정렬한다.

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

src/core/geometry.ts

@@ -331,7 +331,9 @@ export function buildPier(input: PierInput, ctx: PierContext = {}): PierModel {
   };
   const frontPlaced = front.map((b) => ({ no: b.no, row: '전열' as Row, z: b.z, ...place(b) }));
   const backPlaced = back.map((b) => ({ no: b.no, row: '후열' as Row, z: b.z, ...place(b) }));
-  if (unequalRows) { frontPlaced.sort((a,b)=>a.g-b.g); backPlaced.sort((a,b)=>a.g-b.g); }
+  // Rows run along the coping (2026-11-10): bearing numbers may run against IP1 → IP3 (산외교 P9 ① at g 12.1, ③ at 1.3),
+  // so the steps are always built in g order, not number order.
+  frontPlaced.sort((a,b)=>a.g-b.g); backPlaced.sort((a,b)=>a.g-b.g);
 
   // Step boundaries sit midway between consecutive front bearings in coping coordinates (spec §4.3).
   // A step boundary less than half a block from the kink moves onto it (2026-11-10), so the step face is the mitre

tests/kink-steps.test.ts

@@ -115,3 +115,19 @@ describe('꺾임점 계단면 = 미터면 (2026-11-10)', () => {
     expect(topAt(m, backPart(0).profile, kink + DIM.blockSize / 2 + 0.1)).toBeCloseTo(after, 9);
   });
 });
+
+describe('받침 번호가 축 반대 방향인 교각 (2026-11-10)', () => {
+  it('steps are built in g order: bounds rise and each step top is its own bearing seat', () => {
+    // P1 with the bearing numbers reversed in each row (⑤ … ① along IP1 → IP3).
+    const p1 = (() => {
+      const wb = XLSX.read(readFileSync(fileURLToPath(new URL('../도면추출/samples/운곡교P1입력.xlsx', import.meta.url))), { type: 'buffer' });
+      return parseWorkbook(wb).piers.find((p) => p.name === 'P1')!;
+    })();
+    const renumber = (no: number) => (no <= 5 ? 6 - no : 16 - no);
+    const reversed = { ...p1, bearings: p1.bearings.map((b) => ({ ...b, no: renumber(b.no) })) };
+    const a = buildPier(p1), b = buildPier(reversed);
+    for (const m of [a, b]) m.segments.forEach((s) => expect(s.s1).toBeGreaterThan(s.s0));
+    expect(b.segments.map((s) => s.top)).toEqual(a.segments.map((s) => s.top));
+    expect(b.segments.map((s) => s.s0)).toEqual(a.segments.map((s) => s.s0));
+  });
+});