feat(abut): 교대 3D에 받침블럭·몰탈패드와 접속슬래브 추가

- 받침마다 블럭 1200 × 1200 (교좌면 ~ z − 50)과 몰탈패드 1000 × 1000 × 50 (spec §4.2, §6.6). 평면은 교대축 방향
- 접속슬래브 450 두께, 브라켓 상면 위, 흉벽 배면에서 5 mm 떨어져 7 m 배면으로, 배면 쪽 4 % 하향 (spec §4.8). 폭은 날개벽 사이 slabWidthMm, 축 중심
- 부재 표시: 받침·받침블럭 토글이 교대 블럭에도 적용, 접속슬래브 토글 추가
- 테스트 추가 (tests/abut-blocks-slab.test.ts). 전체 634건 통과, 타입 검사·빌드 통과. 브라우저 시각 확인은 미실시

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

src/main.ts

@@ -139,6 +139,8 @@ const state = {
   active: null as string | null,
   view: 'iso' as ViewKind,
   visible: Object.fromEntries(PART_GROUPS.flatMap((g) => g.parts).map((p) => [p, true])) as Record<PartName, boolean>,
+  /** 접속슬래브 toggle (abutments only). */
+  abutSlabVisible: true,
   scene: null as PierScene | null,
   project: { name: '', bridge: '', client: '', author: '', crs: CRS, memo: '' } as ProjectInfo,
   /** Which stage screen is shown: ① 형상 생성 or ② 형상계획 (plan.md C1). */
@@ -358,9 +360,28 @@ function buildPartToggles(): void {
     label.append(input, document.createTextNode(group.label));
     row.appendChild(label);
   }
+  // 접속슬래브 exists only on the abutments (2026-11-03): it has no pier part, so it is kept apart from state.visible.
+  const slabLabel = el('label');
+  const slabInput = el('input');
+  slabInput.type = 'checkbox';
+  slabInput.checked = state.abutSlabVisible;
+  slabInput.addEventListener('change', () => {
+    state.abutSlabVisible = slabInput.checked;
+    setAbutPartVisible('slab', slabInput.checked);
+  });
+  slabLabel.append(slabInput, document.createTextNode('접속슬래브'));
+  row.appendChild(slabLabel);
   box.appendChild(row);
 }
 
+/** Shows or hides one named part of every abutment (the 받침블럭 and 접속슬래브 of abut-scene.ts). */
+function setAbutPartVisible(part: 'blocks' | 'slab', on: boolean): void {
+  for (const g of abutGroups) {
+    const member = g.getObjectByName(part);
+    if (member) member.visible = on;
+  }
+}
+
 function buildViewButtons(): void {
   const box = $<HTMLDivElement>('views');
   for (const v of VIEWS) {
@@ -385,6 +406,8 @@ function setPartVisible(part: PartName, on: boolean): void {
     else for (const s of allPiers.scenes.values()) s.parts.ground.visible = on;
     return;
   }
+  // 받침·받침블럭 also covers the abutments' blocks and pads (2026-11-03).
+  if (part === 'blocks') setAbutPartVisible('blocks', on);
   for (const s of partScenes()) s.parts[part].visible = on;
 }
 
@@ -501,6 +524,11 @@ function setupScene(): void {
         const members = buildMembers(model, { bottomEl: rec.foundationBottomEl, pileLengthMm: rec.pileLengthMm }, rec.shape);
         const group = buildAbutGroup(model, members, buildWings(model, members, rec.wings), ref.pivot, rec.groundEl, groundModel?.terrainGrid);
         group.visible = abutShown(state.stage, state.abutActive, rec.name);
+        // The 부재 표시 toggles hold for a new abutment group too (blocks: the 받침·받침블럭 toggle; slab: 접속슬래브).
+        const blocks = group.getObjectByName('blocks');
+        if (blocks) blocks.visible = state.visible.blocks;
+        const slab = group.getObjectByName('slab');
+        if (slab) slab.visible = state.abutSlabVisible;
         abutGroups.push(group);
         abutGroupByName.set(rec.name, group);
         world.add(group);

src/view/abut-scene.ts

@@ -12,7 +12,36 @@ import { buildWings, type WingSolid } from '../core/abut/wings';
 import type { TerrainGrid } from '../core/ground-model';
 import { terrainGeometry } from './terrain';
 
-export const ABUT_GROUP_NAMES = ['wall', 'parapet', 'footing', 'piles', 'wings', 'haunches', 'ground'] as const;
+export const ABUT_GROUP_NAMES = ['wall', 'parapet', 'footing', 'piles', 'wings', 'haunches', 'ground', 'blocks', 'slab'] as const;
+/** 접속슬래브 두께 (m), spec_abut §4.8. */
+const SLAB_THICKNESS_M = 0.45;
+/** 접속슬래브 길이 (배면 쪽, m), spec_abut §4.8 "7000 (날개벽 축 방향)". */
+const SLAB_LENGTH_M = 7;
+/** 접속슬래브 하향 경사 (배면 쪽으로), spec_abut §4.8 "하향 4 %". */
+const SLAB_FALL = 0.04;
+
+/** Eight-corner slab with its top sloping away from the wall. Indexed by (s end, t end, bottom/top). Double-sided: the winding is not critical. */
+function slabGeometry(s0: number, s1: number, tNear: number, tFar: number, bottomEl: (s: number, t: number) => number): THREE.BufferGeometry {
+  const corners = [s0, s1].flatMap((s) => [tNear, tFar].flatMap((t) => [bottomEl(s, t), bottomEl(s, t) + SLAB_THICKNESS_M].map((y) => [s, y, t])));
+  // index = is * 4 + it * 2 + ih (ih 0 = bottom, 1 = top)
+  const quads = [
+    [0, 2, 3, 1], [4, 5, 7, 6], // s0 and s1 ends
+    [0, 4, 6, 2], [1, 3, 7, 5], // bottom and top
+    [0, 1, 5, 4], [2, 6, 7, 3], // near and far faces (t ends)
+  ];
+  const positions: number[] = [];
+  const indices: number[] = [];
+  for (const q of quads) {
+    const base = positions.length / 3;
+    for (const i of q) positions.push(...corners[i]);
+    indices.push(base, base + 1, base + 2, base, base + 2, base + 3);
+  }
+  const geom = new THREE.BufferGeometry();
+  geom.setAttribute('position', new THREE.Float32BufferAttribute(positions, 3));
+  geom.setIndex(indices);
+  geom.computeVertexNormals();
+  return geom;
+}
 /** 지반 pad margin (m) around the abutment plan, like the pier's GROUND_PAD. */
 export const ABUT_GROUND_MARGIN_M = 2;
 
@@ -134,6 +163,30 @@ export function buildAbutGroup(
     add('footing', prism(footProfile, members.shape.footingThicknessM, new THREE.Vector3(0, footingBottom, 0), ex, ez, ey), 0x5a6a78);
   }
 
+  // 받침블럭 (spec §4.2, §6.6): concrete 1200 × 1200 from the 교좌면 to 50 below z, and the 몰탈패드 1000 × 1000 × 50 up to z.
+  // The plan follows the 교대축 (받침 방위각 = 축 방향). t is the 전면 +, so the bearing's lateral offset is taken with the front side.
+  for (const b of model.bearings) {
+    const t = model.frontSide * b.lateral;
+    const blockTop = b.z - 0.05;
+    add('blocks', prism([[b.s - 0.6, b.seatEl], [b.s + 0.6, b.seatEl], [b.s + 0.6, blockTop], [b.s - 0.6, blockTop]], 1.2, new THREE.Vector3(0, 0, t - 0.6), ex, ey, ez), 0xa9b4bf);
+    add('blocks', prism([[b.s - 0.5, blockTop], [b.s + 0.5, blockTop], [b.s + 0.5, b.z], [b.s - 0.5, b.z]], 1.0, new THREE.Vector3(0, 0, t - 0.5), ex, ey, ez), 0x6e7a86);
+  }
+
+  // 접속슬래브 (spec §4.8): bottom on the 브라켓 top (흉벽 상단 − 0.85), 5 mm behind the 흉벽 back face, 7 m back, falling 4 % away from the wall.
+  // Centred on the axis over the wing-to-wing width (slabWidthMm); the 흉벽 slope along s is followed.
+  const slabW = (model.wing?.slabWidthMm ?? L * 1000) / 1000;
+  const slabNear = members.shape.parapetBackM - 0.005;
+  const bracketTopEl = (s: number) => members.parapetTopStartEl + ((members.parapetTopEndEl - members.parapetTopStartEl) * s) / L - members.shape.bracketHeightM;
+  const slabMesh = new THREE.Mesh(
+    slabGeometry((L - slabW) / 2, (L + slabW) / 2, slabNear, slabNear - SLAB_LENGTH_M, (s, t) => bracketTopEl(s) + SLAB_FALL * (t - slabNear)),
+    new THREE.MeshStandardMaterial({ color: 0xd8c8a0, roughness: 0.9, side: THREE.DoubleSide }),
+  );
+  slabMesh.name = 'slab';
+  const slabGroup = new THREE.Group();
+  slabGroup.name = 'slab';
+  slabGroup.add(slabMesh);
+  root.add(slabGroup);
+
   // 말뚝: D 600 (r 0.3) at each row and bar, from the 기초 하단 down to the 선단.
   if (members.pileBottomEl !== undefined && footingBottom !== undefined) {
     const height = footingBottom - members.pileBottomEl;