feat(maskSplit): computeSplitRegions TDD (v0-plan Task 6)

src/features/maskSplit/splitMask.ts:
- Region / SplitRegions / ImageSize 타입
- 상의(어깨-20 ~ 골반) / 하의(골반 ~ 발목+20) / 전신(어깨-80 ~ 발목+20)
- x 범위: keypoint bbox ±20px
- requireJoint helper: validatePose 통과 후 호출 invariant — 누락 시 explicit throw

src/features/maskSplit/__tests__/splitMask.test.ts:
- 4 케이스 TDD: top / bottom / full y 좌표 + 공통 x 범위

검증:
- npx jest src/features/maskSplit: 4 passed
- npx tsc --noEmit: 무에러

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/features/maskSplit/__tests__/splitMask.test.ts

@@ -0,0 +1,41 @@
+import { computeSplitRegions } from '../splitMask';
+import type { PoseResult } from '../../pose';
+
+describe('computeSplitRegions', () => {
+  const pose: PoseResult = {
+    left_shoulder_joint: { x: 100, y: 200, confidence: 0.9 },
+    right_shoulder_joint: { x: 300, y: 200, confidence: 0.9 },
+    left_hip_joint: { x: 120, y: 400, confidence: 0.85 },
+    right_hip_joint: { x: 280, y: 400, confidence: 0.85 },
+    left_ankle_joint: { x: 130, y: 700, confidence: 0.7 },
+    right_ankle_joint: { x: 270, y: 700, confidence: 0.7 },
+  };
+  const imageSize = { width: 400, height: 800 };
+
+  it('top region은 어깨-20부터 골반까지(목~허리)', () => {
+    const r = computeSplitRegions(pose, imageSize);
+    expect(r.top.yStart).toBe(180);
+    expect(r.top.yEnd).toBe(400);
+  });
+
+  it('bottom region은 골반부터 발목+20까지(허리~발끝)', () => {
+    const r = computeSplitRegions(pose, imageSize);
+    expect(r.bottom.yStart).toBe(400);
+    expect(r.bottom.yEnd).toBe(720);
+  });
+
+  it('full region은 어깨-80부터 발목+20까지(머리위~발끝)', () => {
+    const r = computeSplitRegions(pose, imageSize);
+    expect(r.full.yStart).toBe(120);
+    expect(r.full.yEnd).toBe(720);
+  });
+
+  it('모든 region은 x 범위가 keypoint bbox ±20에 맞춰진다', () => {
+    const r = computeSplitRegions(pose, imageSize);
+    // keypoint x 최소 = 100 (left_shoulder), 최대 = 300 (right_shoulder)
+    expect(r.top.xStart).toBe(80);
+    expect(r.top.xEnd).toBe(320);
+    expect(r.bottom.xStart).toBe(80);
+    expect(r.full.xEnd).toBe(320);
+  });
+});

src/features/maskSplit/splitMask.ts

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+import type { PoseResult, Joint, Keypoint } from '../pose';
+
+export interface Region {
+  xStart: number;
+  yStart: number;
+  xEnd: number;
+  yEnd: number;
+}
+
+export interface SplitRegions {
+  top: Region;
+  bottom: Region;
+  full: Region;
+}
+
+export interface ImageSize {
+  width: number;
+  height: number;
+}
+
+const X_PADDING = 20;
+const TOP_HEAD_MARGIN = 20;
+const FULL_HEAD_MARGIN = 80;
+const FOOT_MARGIN = 20;
+
+function requireJoint(pose: PoseResult, joint: Joint): Keypoint {
+  const kp = pose[joint];
+  if (!kp) throw new Error(`computeSplitRegions: ${joint} keypoint 누락 — validatePose 통과 후 호출 필요`);
+  return kp;
+}
+
+export function computeSplitRegions(
+  pose: PoseResult,
+  _imageSize: ImageSize,
+): SplitRegions {
+  const ls = requireJoint(pose, 'left_shoulder_joint');
+  const rs = requireJoint(pose, 'right_shoulder_joint');
+  const lh = requireJoint(pose, 'left_hip_joint');
+  const rh = requireJoint(pose, 'right_hip_joint');
+  const la = requireJoint(pose, 'left_ankle_joint');
+  const ra = requireJoint(pose, 'right_ankle_joint');
+
+  const shoulderY = Math.min(ls.y, rs.y);
+  const hipY = Math.max(lh.y, rh.y);
+  const ankleY = Math.max(la.y, ra.y);
+  const xMin = Math.min(ls.x, rs.x, lh.x, rh.x, la.x, ra.x) - X_PADDING;
+  const xMax = Math.max(ls.x, rs.x, lh.x, rh.x, la.x, ra.x) + X_PADDING;
+
+  return {
+    top: { xStart: xMin, yStart: shoulderY - TOP_HEAD_MARGIN, xEnd: xMax, yEnd: hipY },
+    bottom: { xStart: xMin, yStart: hipY, xEnd: xMax, yEnd: ankleY + FOOT_MARGIN },
+    full: { xStart: xMin, yStart: shoulderY - FULL_HEAD_MARGIN, xEnd: xMax, yEnd: ankleY + FOOT_MARGIN },
+  };
+}