feat(user): username 对外展示 + 默认昵称 + 存量回填

代提工作区既有的他人在制品(非本次 CPS);CPS 迁移链 cps_tables 依赖其
b3f1a2c4d5e6 迁移,需一并提交。

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

tests/test_auth.py

@@ -206,3 +206,40 @@ def test_sms_gc_purges_stale_only(monkeypatch) -> None:
     assert "stale" not in sms._codes and "fresh" in sms._codes
     assert "old" not in sms._last_sent and "recent" in sms._last_sent
     assert "yesterday" not in sms._daily_count and "today" in sms._daily_count
+
+
+# ============================ 用户名 / 默认昵称 ============================
+
+def test_login_assigns_username_and_nickname(client) -> None:
+    """新用户创建即分配:11 位纯数字 username(首位非 0/1,与手机号天然区分)+ 9 位字母数字默认昵称。"""
+    phone = "13600136000"
+    client.post("/api/v1/auth/sms/send", json={"phone": phone})
+    r = client.post("/api/v1/auth/sms/login", json={"phone": phone, "code": "123456"})
+    assert r.status_code == 200, r.text
+    user = r.json()["user"]
+
+    uname = user["username"]
+    assert uname.isdigit() and len(uname) == 11          # 11 位纯数字
+    assert uname[0] not in ("0", "1")                     # 无前导 0、与手机号(均以 1 开头)区分
+
+    nick = user["nickname"]
+    assert nick and len(nick) == 9 and nick.isalnum()     # 9 位字母+数字
+
+
+def test_username_stable_and_unique_on_relogin() -> None:
+    """同号重登 username 不变(不可变标识);不同号 username 不同(唯一)。
+    直连 repository 绕开 HTTP 短信冷却。"""
+    from app.db.session import SessionLocal
+    from app.repositories import user as user_repo
+
+    db = SessionLocal()
+    try:
+        a1 = user_repo.upsert_user_for_login(db, phone="13522220001", register_channel="sms")
+        uname_a, id_a = a1.username, a1.id
+        a2 = user_repo.upsert_user_for_login(db, phone="13522220001", register_channel="sms")
+        assert a2.id == id_a and a2.username == uname_a    # 重登:同一行、username 稳定不变
+
+        b = user_repo.upsert_user_for_login(db, phone="13522220002", register_channel="sms")
+        assert b.username != uname_a                        # 不同用户、username 唯一
+    finally:
+        db.close()