test(rebar): the footing rebar follows the footing inputs (L, W, H); P1 unchanged

The B-bar counts are computed from the footing dimensions already, so no formula change was needed. Tests check the P1
values, that a wider and longer footing adds B1–B8 bars, and that a 2200 mm height builds rebar and 3D.

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

tests/footing-rebar-inputs.test.ts

@@ -0,0 +1,30 @@
+import { describe, expect, it } from 'vitest';
+import { buildPier } from '../src/core/geometry';
+import { buildRebar3D } from '../src/view/rebar3d';
+import { rebarSummary } from '../src/core/rebar/summary';
+import { loadP1 } from './helpers';
+
+const footingRows = (input: Parameters<typeof buildPier>[0]) =>
+  rebarSummary(buildPier(input)).rows.filter((r) => r.member === 'footing');
+const count = (rows: ReturnType<typeof footingRows>, name: string) => rows.find((r) => r.name === name)!.count;
+
+describe('확대기초 철근은 입력 치수를 따른다 (3단계, 승인 2026-10-23)', () => {
+  it('P1 footing rebar is unchanged with the default inputs (B1 31, B5 40, B9 306)', () => {
+    const rows = footingRows(loadP1());
+    expect(count(rows, 'B1')).toBe(31);
+    expect(count(rows, 'B5')).toBe(40);
+    expect(count(rows, 'B9')).toBe(306);
+  });
+
+  it('a wider footing (W 9000) and a longer one (L 11000) add bars to B1–B4 and B5–B8', () => {
+    const rows = footingRows({ ...loadP1(), footingWidthMm: 9000, footingLengthMm: 11000 });
+    expect(count(rows, 'B1')).toBeGreaterThan(31);
+    expect(count(rows, 'B5')).toBeGreaterThan(40);
+  });
+
+  it('a different footing height (2200) is computed without error, and the 3D rebar still builds', () => {
+    const m = buildPier({ ...loadP1(), footingHeightMm: 2200 });
+    expect(rebarSummary(m).rows.length).toBeGreaterThan(0);
+    expect(buildRebar3D(m).byName.get('B1')!.length).toBeGreaterThan(0);
+  });
+});