fix(abut): 수축줄눈을 받침 사이 중간에 · 기본 개수 ceil(L/10) − 1 · 3D 선 표시

spec_abut §3 · §4.9 (QA-7 가정)와 맞지 않던 세 가지를 고친다.
- 위치: 등분점(1개면 L/2)이 아니라 가장 가까운 '받침 사이 중간'(= 교좌면 계단 경계). 이전에는 운곡교 교대
  5기 모두 줄눈이 가운데 받침 ③ 블럭을 지났다 (A1: 줄눈 6.099 · 받침 6.037). 이제 A1은 IP3에서 4.905 m
- 개수: 입력이 없으면 ceil(L/10) − 1 (길이에 따라 자동, 이전에는 1 고정). 입력 칸은 비우면 자동
- 3D: 벽체 전면 · 흉벽 전면 · 벽체 배면 · 흉벽 배면에 선으로 표시(저판은 연속이라 없음), '벽체·흉벽' 토글을 따름
- 공통 계산 core/abut/joints.ts를 ② 정면·배면 삽도, 교대 상세 요약, 입력 칸 안내, 3D가 함께 씀
- 테스트: 개수 규칙, A1 위치 = ②·③ 중간 = 계단 경계, 여러 개 · 받침 부족 시 등분, 3D 선 4면

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

tests/abut-joints.test.ts

@@ -0,0 +1,43 @@
+import * as THREE from 'three';
+import { describe, expect, it } from 'vitest';
+import { defaultJointCount, jointCount, jointPositions } from '../src/core/abut/joints';
+import { buildAbut } from '../src/core/abut/geometry';
+import { parseAbutments, toAbutInput } from '../src/core/abut/parse';
+import { buildMembers } from '../src/core/abut/members';
+import { buildAbutGroup } from '../src/view/abut-scene';
+import { loadInputWorkbook } from './helpers';
+
+// 교대 수축줄눈 (spec_abut §3 · §4.9, QA-7): count ceil(L/10) − 1, position = the middle between the nearest bearings.
+const rec = parseAbutments(loadInputWorkbook()).abutments.find((a) => a.name === 'A1')!;
+const model = buildAbut(toAbutInput(rec));
+const bearingS = model.bearings.map((b) => b.s);
+
+describe('교대 수축줄눈', () => {
+  it('count: ceil(L/10) − 1 by default (12.197 → 1, 20 → 1, 20.5 → 2, 9 → 0), a typed count wins', () => {
+    expect([12.197, 20, 20.5, 9].map(defaultJointCount)).toEqual([1, 1, 2, 0]);
+    expect(jointCount(12.197, 3)).toBe(3);
+  });
+
+  it('A1: the joint is not on bearing ③ (L/2) but in the middle between ② and ③, which is the 교좌면 step boundary', () => {
+    const [s] = jointPositions(model.length, bearingS);
+    const sorted = [...bearingS].sort((a, b) => a - b);
+    expect(s).toBeCloseTo((sorted[2] + sorted[3]) / 2, 9);
+    expect(Math.min(...bearingS.map((b) => Math.abs(b - s)))).toBeGreaterThan(0.6 + 0.6);
+    expect(model.stepBounds.some((x) => Math.abs(x - s) < 1e-3)).toBe(true);
+  });
+
+  it('several joints take distinct midpoints nearest to the even split; without enough bearings, the even split', () => {
+    const js = jointPositions(model.length, bearingS, 2);
+    expect(new Set(js.map((x) => x.toFixed(6))).size).toBe(2);
+    expect(jointPositions(30, [5], 2)).toEqual([10, 20]);
+  });
+
+  it('3D: one line on each of the four 벽체 · 흉벽 faces per joint, none in the 저판', () => {
+    const members = buildMembers(model, { bottomEl: rec.foundationBottomEl, pileLengthMm: rec.pileLengthMm });
+    const group = buildAbutGroup(model, members);
+    const lines = group.getObjectByName('joints')!.children[0] as THREE.LineSegments;
+    const pos = lines.geometry.getAttribute('position') as THREE.BufferAttribute;
+    expect(pos.count).toBe(4 * 2);
+    for (let i = 0; i < pos.count; i++) expect(pos.getY(i)).toBeGreaterThanOrEqual(members.footingTopEl - 1e-5);
+  });
+});

tests/abut-summary.test.ts

@@ -20,7 +20,8 @@ describe('교대 상세 (삽도 항목, spec_abut §10.1)', () => {
   it('the piles, joints, 접속슬래브 width and 받침블럭 height match the spec: 18 piles, tip 19.295, 1 joint, 11253 mm, 125 mm', () => {
     expect(rows.get('말뚝 (열 × 본수)')).toBe('3 × 6 = 18 본');
     expect(rows.get('말뚝 선단 EL')).toBe('19.295 m');
-    expect(rows.get('수축줄눈 (ceil(L/10) − 1)')).toBe('1 개');
+    // 1 joint (ceil(12.197/10) − 1), moved from L/2 (on bearing ③) to the middle between ② and ③ (2026-11-06).
+    expect(rows.get('수축줄눈 (기본 ceil(L/10) − 1, 받침 사이 중간)')).toMatch(/^1 개 · IP3에서 4\.90[45] m$/);
     // 11.2535 m exactly (450 / sin Δ + 20 per wing); rounding to mm gives 11253 or 11254.
     expect(Math.abs(parseInt(String(rows.get('접속슬래브 폭')), 10) - 11253)).toBeLessThanOrEqual(1);
     expect(rows.get('받침블럭 높이 (패드 포함)')).toBe('125 mm');

tests/abut-wall-svg.test.ts

@@ -1,3 +1,4 @@
+import { jointPositions } from '../src/core/abut/joints';
 import { readFileSync } from 'node:fs';
 import { fileURLToPath } from 'node:url';
 import * as XLSX from 'xlsx';
@@ -26,7 +27,7 @@ const d: AbutWallDrawing = {
   footingFrontM: m.shape.footingFrontM,
   footingBackM: m.shape.footingBackM,
   bracketHeightM: m.shape.bracketHeightM,
-  shrinkJointCount: 1,
+  shrinkJointsS: jointPositions(model.length, model.bearings.map((b) => b.s)),
   bracketWidthMm: 300,
   parapetThicknessMm: 500,
   seatWidthMm: 1600,
@@ -50,7 +51,7 @@ describe('교대 벽체·흉벽 삽도 (시안 ② 벽체·흉벽 카드)', () =
   });
 
   it('the 수축줄눈 count follows the input', () => {
-    const svg = abutWallElevationSvg({ ...d, shrinkJointCount: 2 });
+    const svg = abutWallElevationSvg({ ...d, shrinkJointsS: jointPositions(model.length, model.bearings.map((b) => b.s), 2) });
     expect(svg).toContain('수축줄눈 2');
     expect(svg.match(/stroke-dasharray="5 3"/g)).toHaveLength(2);
   });