feat(接口2): C端生发发际线预览(真实实现，替换Mock)

第一步：按性别把发际线类型贴图渲染到照片，输出 N 张发际线叠加预览图。

- hairline/render.py: 解析 face_ext.obj(502 UV + 64 ribbon扩展面) + OpenCV 逐三角
  仿射 warp 渲染器；关键修复——face_ext.obj 是 OBJ序，用 INDEX_MAP_468 把 MP序
  502点重排成 OBJ序后再投影，否则 ribbon 会错贴到中脸
- hairline/service.py: FaceLandmarker+SegFormer 单例 + 性别贴图映射(扫描去空格)
  + generate_previews 管线(female5/male4)
- 集成点修复: face_landmarks DEFAULT_MODEL_PATH 改 hairline/models/;
  constants HF_FACE_PARSER_MODEL 改本地路径(离线)
- app.py: /api/v1/hair/grow 接真实实现，gender 必填(非法→1004)，返回
  results[].image_base64(不落盘)，校验/鉴权同接口1；lifespan 预热接口2单例；
  补 logging.basicConfig
- 依赖: transformers==4.45.2；SegFormer 权重走 hf-mirror 下载(见 OFFLINE_ASSETS)
- 测试: tests/test_hairline.py(mesh/重排/贴图映射) + test_api 接口2用例，31 全绿

注：SegFormer 受 5090/torch 限制走 CPU(~2.5s/张)，换 cu128 可 SEG_DEVICE=cuda。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_api.py

@@ -72,6 +72,27 @@ def test_corrupt_1008(client):
     assert r.json()["code"] == 1008
 
 
+GROW = "/api/v1/hair/grow"
+
+
+def test_grow_missing_gender_1004(client):
+    files = {"image_file": ("frontal.jpg", open(fixture("frontal.jpg"), "rb"), "application/octet-stream")}
+    r = client.post(GROW, headers=H, files=files)
+    assert r.json()["code"] == 1004
+
+
+def test_grow_female_returns_5(client):
+    files = {"image_file": ("frontal.jpg", open(fixture("frontal.jpg"), "rb"), "application/octet-stream")}
+    r = client.post(GROW, headers=H, files=files, data={"gender": "female"})
+    body = r.json()
+    assert body["code"] == 0, body
+    results = body["data"]["results"]
+    assert [x["hairline_type"] for x in results] == ["ellipse", "flower", "heart", "straight", "wave"]
+    assert [x["order"] for x in results] == [1, 2, 3, 4, 5]
+    assert base64.b64decode(results[0]["image_base64"])[:8] == b"\x89PNG\r\n\x1a\n"
+    assert "image_url" not in results[0]
+
+
 def test_success_structure(client):
     r = _post(client, "frontal.jpg")
     body = r.json()

tests/test_hairline.py

@@ -0,0 +1,31 @@
+"""接口2 单元测试：mesh 解析 / MP→OBJ 重排 / 性别贴图映射（不需 SegFormer）。"""
+import numpy as np
+
+from hairline.render import load_ext_mesh, mp_order_to_obj_order
+from hairline.service import get_texture_map
+from hairline import constants as C
+
+
+def test_ext_mesh():
+    uv, ext_faces = load_ext_mesh()
+    assert uv.shape == (502, 2)
+    assert len(ext_faces) == 64                     # ribbon 扩展三角形
+    # 扩展面至少含一个 ≥468 的顶点
+    assert all(max(f) >= 468 for f in ext_faces)
+
+
+def test_mp_to_obj_anchor_mapping():
+    """OBJ 序重排后，ribbon 引用的 obj 锚点应映射回 MP_TOP_ANCHORS。"""
+    pts = np.zeros((502, 3), np.float32)
+    pts[:468, 0] = np.arange(468)                   # 用 x 编码 MP 索引
+    obj = mp_order_to_obj_order(pts)
+    _uv, ext_faces = load_ext_mesh()
+    obj_anchor_ids = sorted({pi for f in ext_faces for pi in f if pi < 468})
+    mapped = sorted(int(obj[i, 0]) for i in obj_anchor_ids)   # 还原成 MP 索引
+    assert mapped == sorted(C.MP_TOP_ANCHORS)
+
+
+def test_texture_map():
+    m = get_texture_map()
+    assert [k for k, _ in m["female"]] == ["ellipse", "flower", "heart", "straight", "wave"]
+    assert [k for k, _ in m["male"]] == ["ellipse", "inverse_arc", "m", "straight"]