diff --git a/yunke-server/app/analytics/lifecycle.py b/yunke-server/app/analytics/lifecycle.py
new file mode 100644
index 0000000..7813b33
--- /dev/null
+++ b/yunke-server/app/analytics/lifecycle.py
@@ -0,0 +1,71 @@
+"""客户生命周期判定(管理域,批次A)——距今天数口径(v2 §1.1 #3 决议)。
+
+阈值取已确认默认(v1 §21,用户拍板):新客 7 天、沉睡 30 天;历史互动
+门槛 MIN_HISTORY_MSGS=5 对齐 analytics churn real 的 min_msgs=5。
+analytics 现有页(churn/客户资产)**暂不切换**到此模块——两套数字的
+差异在 metric-definitions 标注(v2 §5);后续统一时再接,避免动既有
+测试。
+
+本模块为纯叶子节点,禁止 import app.storage(防止 storage→analytics
+消费时成环)。
+"""
+
+from __future__ import annotations
+
+import datetime as dt
+
+NEW_DAYS = 7
+DORMANT_DAYS = 30
+MIN_HISTORY_MSGS = 5
+
+STATES = ("new", "active", "cooling", "dormant", "reactivated")
+
+
+def _to_date(day: int) -> dt.date:
+    return dt.date(day // 10000, (day // 100) % 100, day % 100)
+
+
+def day_add(day: int, delta_days: int) -> int:
+    """yyyymmdd 键加减天数。"""
+    d = _to_date(day) + dt.timedelta(days=delta_days)
+    return d.year * 10000 + d.month * 100 + d.day
+
+
+def days_between(day_a: int, day_b: int) -> int:
+    """b − a 的天数(输入 yyyymmdd 键)。"""
+    return (_to_date(day_b) - _to_date(day_a)).days
+
+
+def classify(
+    first_day: int | None,
+    last_day: int | None,
+    prev_day: int | None,
+    as_of: int,
+    hist_msgs: int,
+) -> str | None:
+    """as_of 日的客户状态;输入均为互动日键(yyyymmdd,上海自然日)。
+
+    - first_day: 该客户全历史首次互动日;last_day: ≤as_of 的最近互动日;
+      prev_day: last_day 之前的一次互动日(无则 None);hist_msgs: 历史总消息数。
+    - 返回 None = 未激活(first/last 缺)或历史不足的长期静默(不计入任何列)。
+
+    判定优先级:new → reactivated → active → cooling → dormant。
+    """
+    if first_day is None or last_day is None:
+        return None
+    if first_day >= day_add(as_of, -(NEW_DAYS - 1)):
+        return "new"
+    if (
+        last_day == as_of
+        and prev_day is not None
+        and days_between(prev_day, last_day) > DORMANT_DAYS
+    ):
+        return "reactivated"
+    gap = days_between(last_day, as_of)
+    if gap < NEW_DAYS:
+        return "active"
+    if gap < DORMANT_DAYS:
+        return "cooling"
+    if hist_msgs >= MIN_HISTORY_MSGS:
+        return "dormant"
+    return None
diff --git a/yunke-server/tests/test_lifecycle.py b/yunke-server/tests/test_lifecycle.py
new file mode 100644
index 0000000..490b4d9
--- /dev/null
+++ b/yunke-server/tests/test_lifecycle.py
@@ -0,0 +1,72 @@
+"""客户生命周期判定纯函数测试(批次A Task4)。
+
+口径(v2 §1.1 #3 + v1 §21 默认,已用户确认):新客 7 天、沉睡 30 天、
+历史≥5 条才算沉睡(对齐 churn real min_msgs=5)。analytics 现有页
+(churn/客户资产)暂不切换(口径差异 v2 §5 标注),不动 636 既有测试。
+"""
+
+from app.analytics.lifecycle import DORMANT_DAYS, MIN_HISTORY_MSGS, NEW_DAYS, classify, day_add
+
+
+def test_constants_locked_to_confirmed_defaults():
+    assert NEW_DAYS == 7 and DORMANT_DAYS == 30 and MIN_HISTORY_MSGS == 5
+
+
+def test_new_customer():
+    # 首次沟通在 7 天窗口内
+    assert (
+        classify(first_day=20260901, last_day=20260903, prev_day=None, as_of=20260905, hist_msgs=2)
+        == "new"
+    )
+    # 窗口边界:as_of-6=20260830 含当天共 7 天 → new;再早一天 → 非 new
+    assert classify(20260830, 20260830, None, 20260905, 100) == "new"
+    assert classify(20260829, 20260829, None, 20260905, 100) == "cooling"
+
+
+def test_reactivated_requires_gap_over_30d():
+    # 当日回流且前次间隔>30 天
+    assert (
+        classify(
+            first_day=20260101, last_day=20260905, prev_day=20260801, as_of=20260905, hist_msgs=50
+        )
+        == "reactivated"
+    )
+    # 间隔仅 9 天 → 只是 active
+    assert (
+        classify(
+            first_day=20260101, last_day=20260905, prev_day=20260827, as_of=20260905, hist_msgs=50
+        )
+        == "active"
+    )
+    # 间隔恰好 30 天 → 严格 >30 不算回流,落回 active
+    assert (
+        classify(
+            first_day=20260101, last_day=20260905, prev_day=20260806, as_of=20260905, hist_msgs=50
+        )
+        == "active"
+    )
+    # 回流必须当日互动:前次间隔 31 天(>30)但 last_day=as_of-1 → 不算回流,按 gap=1 落 active
+    assert classify(20260101, 20260904, 20260804, 20260905, 50) == "active"
+
+
+def test_active_cooling_dormant_boundaries():
+    f, m = 20260101, 100
+    assert classify(f, 20260830, None, 20260905, m) == "active"  # 6 天
+    assert classify(f, 20260829, None, 20260905, m) == "cooling"  # 7 天
+    assert classify(f, 20260807, None, 20260905, m) == "cooling"  # 29 天
+    assert classify(f, 20260806, None, 20260905, m) == "dormant"  # 30 天
+
+
+def test_dormant_requires_history():
+    # ≥30 天无互动但历史<5 条:不计入任何状态(None)
+    assert classify(20260101, 20260806, None, 20260905, 4) is None
+    assert classify(20260101, 20260806, None, 20260905, 5) == "dormant"
+
+
+def test_no_interaction_returns_none():
+    assert classify(None, None, None, 20260905, 0) is None
+
+
+def test_day_add():
+    assert day_add(20260831, 1) == 20260901
+    assert day_add(20260901, -7) == 20260825