fix(alerts): deterministic tiebreaker for paginated alert list

list_alerts ordered by created_at DESC alone; kpi_alerts has many rows sharing the same second timestamp (07:00 batches), so MySQL tie order is unstable and offset pagination both duplicated and skipped rows (entity 1 read-only probe: total=281, 281 rows walked, only 268 unique ids, 13 duplicates; id 587 unreachable in the unfiltered list while visible in ?status=pending).

Add secondary key id DESC so pages form a total order; add regression suite test_alerts_pagination_stability_20260925.py (tie-heavy fixture: unique==total, zero duplicates, strict id DESC inside a tie group, page concat == single-shot ordered query, unfiltered vs status-filtered visibility, entity isolation negative control).

backend/app/api/alerts.py

@@ -23,7 +23,13 @@ def list_alerts(status: str = None, page: int = Query(1, ge=1), db: Session = De
     if status:
         query = query.filter(KPIAlert.status == status)
     total = query.count()
-    alerts = query.order_by(KPIAlert.created_at.desc()).offset((page-1)*20).limit(20).all()
+    # 分页确定性(2026-09-25 alerts-list-pagination-skip)：原为 created_at.desc() **单键** +
+    # offset/limit — kpi_alerts 每批 07:00 生成、**大量行同秒 created_at**，MySQL 并列组内顺序
+    # 不确定 ⇒ 偏移分页重复并漏行（entity 1 只读实测：total=281 / 逐页取满 281 行 / 唯一 id 仅 268 /
+    # 重复 13；id=587 在无过滤列表不可达，而同行 ?status=pending 首屏正常可见）。
+    # 补**确定性次键** id.desc()（同秒内后写入者在前）→ 全序分页，逐页遍历可覆盖全部 total 行。
+    alerts = (query.order_by(KPIAlert.created_at.desc(), KPIAlert.id.desc())
+              .offset((page-1)*20).limit(20).all())
     return {"total": total, "data": [{c.name: getattr(a, c.name) for c in KPIAlert.__table__.columns} for a in alerts]}
 
 @router.post("/{alert_id}/resolve")

backend/tests/test_alerts_pagination_stability_20260925.py

@@ -0,0 +1,169 @@
+# -*- coding: utf-8 -*-
+"""`GET /api/cma/alerts` 无过滤列表分页可及性回归（任务 fullstack-20260925-alerts-list-pagination-skip）
+
+缺陷（改前既有，2026-09-25 生产只读实测）：`app/api/alerts.py::list_alerts` 用
+`ORDER BY created_at DESC` **单键** + `offset/limit` 分页；`kpi_alerts` 每批 07:00 生成，
+**大量行同秒 created_at** ⇒ MySQL filesort 在并列组内顺序不确定，偏移分页会**重复并漏行**
+（entity 1 实测：total=281、逐页取满 281 行、唯一 id 仅 **268**、重复 13；id=587 因此
+不出现在无过滤列表，而同行的 `?status=pending` 列表首屏正常可见）。
+
+修复：排序补**确定性次键** `id DESC` ⇒ 同一 `created_at` 内按 id 降序（= 同秒内后写入者在前），
+偏移分页成为全序分页，逐页遍历可覆盖全部 total 行且零重复。
+
+本套件判据（改前 RED / 改后 GREEN）：
+  · T1 唯一性：逐页取满后 `唯一 id 数 == total` 且 `重复 == 0`；
+  · T2 确定性次键：并列 `created_at` 组内 id **严格降序**（改前同一夹具下为插入序 = 升序 → RED）；
+  · T3 逐页序列 == 「一次性全量取」（无分页）按 (created_at desc, id desc) 的序列，逐项相同；
+  · T4 可见性一致：同一行在「无过滤遍历」与「?status=pending 遍历」中一致可见（587 型）；
+  · T5 负对照（非回归）：账套隔离未放宽 —— 他账套行不出现在本账套列表；跨时间戳仍「新→旧」。
+"""
+from datetime import datetime, timedelta
+
+from fastapi.testclient import TestClient
+from sqlalchemy.orm import Session
+
+from app.models import KPIAlert
+from tests.conftest import create_test_user, get_token_for_user, auth_header, create_test_kpi
+
+PAGE_SIZE = 20  # app/api/alerts.py 硬编码 limit(20)
+
+#: 固定「同秒」时间戳 —— 全部并列行共用，复刻生产「每批 07:00 生成、同秒 created_at」形态
+SAME_SECOND = datetime(2026, 9, 20, 7, 0, 42)
+
+
+def _alert(db: Session, kpi_id: int, **kw) -> KPIAlert:
+    defaults = {
+        "kpi_id": kpi_id,
+        "entity_id": 1,
+        "alert_level": "yellow",
+        "alert_message": "分页夹具",
+        "status": "pending",
+        "created_at": SAME_SECOND,
+    }
+    defaults.update(kw)
+    a = KPIAlert(**defaults)
+    db.add(a)
+    db.commit()
+    db.refresh(a)
+    return a
+
+
+def _walk(client: TestClient, token: str, status: str = None) -> dict:
+    """逐页调用真实端点，直到某页不足 PAGE_SIZE 行（= 前端/调用方遍历姿势）。"""
+    url = "/api/cma/alerts" + (f"?status={status}" if status else "")
+    pages, seen, dups, rows = [], [], [], []
+    page = 1
+    total = None
+    while True:
+        sep = "&" if "?" in url else "?"
+        resp = client.get(f"{url}{sep}page={page}", headers=auth_header(token))
+        assert resp.status_code == 200, resp.text
+        body = resp.json()
+        if total is None:
+            total = body["total"]
+        ids = [r["id"] for r in body["data"]]
+        for pos, r in enumerate(body["data"]):
+            if r["id"] in seen:
+                dups.append({"id": r["id"], "page": page, "pos": pos})
+            else:
+                seen.append(r["id"])
+            rows.append(r)
+        pages.append(ids)
+        if len(ids) < PAGE_SIZE:
+            break
+        page += 1
+        assert page < 100, "分页遍历未终止（保险丝）"
+    return {"total": total, "pages": pages, "unique": seen, "dups": dups, "rows": rows}
+
+
+def _tie_groups(rows):
+    groups = {}
+    for r in rows:
+        groups.setdefault(str(r["created_at"]), []).append(r["id"])
+    return groups
+
+
+class TestAlertsListPaginationAccessibility:
+    """分页可及性（判据主体；改前 T1/T2/T3 应为 RED）"""
+
+    def test_t1_t2_t3_tie_heavy_batch_all_rows_reachable_and_deterministic(
+            self, client: TestClient, db: Session):
+        """61 条同秒 + 5 条跨时间戳：逐页取满 ⇒ 唯一==total、零重复、并列组 id 降序、与全量序列一致"""
+        create_test_user(db)
+        token = get_token_for_user(client)
+        kpi = create_test_kpi(db)
+
+        # 61 条同秒（>3 页，且每页必然出现「并列组跨界」）+ 5 条更早的（跨时间戳排序正对照）
+        tie_ids = [_alert(db, kpi.id).id for _ in range(61)]
+        older_ids = [_alert(db, kpi.id, created_at=SAME_SECOND - timedelta(hours=1)).id for _ in range(5)]
+        total_expected = 66
+
+        w = _walk(client, token, None)
+        assert w["total"] == total_expected, w["total"]
+
+        # T1 唯一性与重复
+        assert len(set(w["unique"])) == w["total"], (
+            f"逐页遍历唯一 id 数 {len(set(w['unique']))} != total {w['total']}；重复 {w['dups']}")
+        assert w["dups"] == [], f"偏移分页出现重复行：{w['dups']}"
+        assert len(w["unique"]) == w["total"], "逐页取到的行数应等于 total"
+
+        # T2 确定性次键：并列组内 id 严格降序
+        for ca, ids in _tie_groups(w["rows"]).items():
+            if len(ids) > 1:
+                assert ids == sorted(ids, reverse=True), (
+                    f"created_at={ca} 并列组内未按 id 降序（分页顺序不确定）：{ids}")
+
+        # T3 逐页拼接序列 == 一次性全量取（不同查询路径：单次全量 ORM 查询，显式两键排序）
+        full = (db.query(KPIAlert)
+                .filter(KPIAlert.entity_id == 1)
+                .order_by(KPIAlert.created_at.desc(), KPIAlert.id.desc())
+                .all())
+        assert [r["id"] for r in w["rows"]] == [a.id for a in full], "逐页序列与全量排序序列不一致"
+        # 全量序列 = 5 条跨时间戳（新→旧）+ 61 条同秒（id 降序）
+        assert [r["id"] for r in w["rows"]][:5] == sorted(tie_ids, reverse=True)[:5]
+        assert set(w["unique"]) == set(tie_ids) | set(older_ids)
+
+    def test_t4_visibility_consistent_between_unfiltered_and_status_filtered(
+            self, client: TestClient, db: Session):
+        """同一行在无过滤遍历与 ?status=pending 遍历中一致可见（587 型：待办不得翻页翻不到）"""
+        create_test_user(db)
+        token = get_token_for_user(client)
+        kpi = create_test_kpi(db)
+
+        # 65 条同秒 pending（>3 页）+ 3 条同秒 resolved（无过滤列表里夹在并列组中）
+        pending_ids = [_alert(db, kpi.id, status="pending").id for _ in range(65)]
+        _alert_ids = [_alert(db, kpi.id, status="resolved").id for _ in range(3)]
+        oldest_pending = min(pending_ids)  # 深页行：改前最易被漏读
+
+        unf = _walk(client, token, None)
+        pend = _walk(client, token, "pending")
+
+        assert unf["total"] == 68 and pend["total"] == 65
+        assert len(set(unf["unique"])) == unf["total"], "无过滤列表漏读"
+        assert len(set(pend["unique"])) == pend["total"], "pending 列表漏读"
+        assert oldest_pending in unf["unique"], "深页 pending 行在无过滤列表不可达（改前 RED 形态）"
+        assert oldest_pending in pend["unique"], "深页 pending 行在 pending 列表不可达"
+        for aid in pending_ids:
+            assert aid in unf["unique"], f"pending 行 {aid} 在无过滤列表不可达"
+        assert set(unf["unique"]) == set(pending_ids) | set(_alert_ids)
+
+    def test_t5_entity_isolation_and_cross_timestamp_order_unchanged(
+            self, client: TestClient, db: Session):
+        """负对照：账套隔离未放宽（他账套行不可见）+ 跨时间戳仍「新→旧」"""
+        create_test_user(db)
+        token = get_token_for_user(client)
+        kpi = create_test_kpi(db)
+
+        mine = [_alert(db, kpi.id, created_at=SAME_SECOND - timedelta(days=2)).id for _ in range(30)]
+        other = [_alert(db, kpi.id, entity_id=2, created_at=SAME_SECOND).id for _ in range(30)]
+        # 本账套另有 6 条更新的行（**时间戳互不相同** → 无并列，纯跨时间戳正对照）：
+        # 必须排在他账套「同秒组」之前，且按新→旧；改前改后都应通过（本用例是非回归负对照）
+        newer = [_alert(db, kpi.id,
+                        created_at=SAME_SECOND + timedelta(hours=i + 1)).id for i in range(6)]
+        newer_expected = list(reversed(newer))  # 最新的一条（+6h）在最前
+
+        w = _walk(client, token, None)
+        assert w["total"] == len(mine) + len(newer), "账套隔离被放宽：他账套行进入本账套列表"
+        assert not (set(other) & set(w["unique"])), "他账套行泄漏进本账套列表"
+        assert [r["id"] for r in w["rows"]][:6] == newer_expected, "跨时间戳未按新→旧排序"
+        assert set(w["unique"]) == set(mine) | set(newer)