风控列表游标绑定用户与查询条件（docs/25 遗留 P3）

docs/05 §3.8 要求游标绑定用户、查询条件、排序字段和方向，此前实现只把 offset
用 base64 包了一层：任何登录用户拿到别人的游标都能继续翻，换个筛选条件也能继续翻
（偏移量对不上就静默返回错页）。现在游标里携带 SHA-256 指纹：

- 指纹口径 = user_id + data_scope/customer_ids + 查询条件（排除 limit/cursor）
- 刻意排除 limit：它是分页参数、不是查询条件，算进去只会让翻页时改页大小失效
- /evidence/{source} 的 source 是路径参数，单独并入指纹，否则 customers 的
  游标能直接拿去翻 products
- 指纹不符一律 InvalidCursorError -> 400 INVALID_CURSOR（docs/05 §3.6）

新增 2 个单测：换用户/换筛选/换 data_scope 失效、改 limit 仍有效、
不同证据类型游标不互通。

tests/unit/service/test_risk_query_service.py

@@ -7,7 +7,7 @@ import pytest
 from app.api.schemas.risk import RiskAlertPageQuery, RiskEvidencePageQuery
 from app.core.contracts import RequestContext
 from app.core.errors import GenericResourceNotFoundError, InvalidCursorError
-from app.core.risk_cursor import decode_offset_cursor, encode_offset_cursor
+from app.core.risk_cursor import cursor_binding, decode_offset_cursor, encode_offset_cursor
 from app.repository.fund_query_repository import CustomerScope, FundPage, FundRecord
 from app.service.risk_query_service import RiskQueryService, scope_from_context
 
@@ -64,12 +64,15 @@ def context(**updates) -> RequestContext:
 
 
 def test_cursor_round_trip_and_invalid_values() -> None:
-    assert decode_offset_cursor(encode_offset_cursor(20)) == 20
-    assert decode_offset_cursor(None) == 0
+    binding = cursor_binding(user_id="990000002", filters={"keyword": None})
+    assert (
+        decode_offset_cursor(encode_offset_cursor(20, binding=binding), binding=binding) == 20
+    )
+    assert decode_offset_cursor(None, binding=binding) == 0
     with pytest.raises(InvalidCursorError):
-        decode_offset_cursor("not-a-cursor")
+        decode_offset_cursor("not-a-cursor", binding=binding)
     with pytest.raises(InvalidCursorError):
-        decode_offset_cursor(encode_offset_cursor(1) + "x")
+        decode_offset_cursor(encode_offset_cursor(1, binding=binding) + "x", binding=binding)
 
 
 def test_query_schema_enforces_business_page_sizes() -> None:
@@ -105,14 +108,55 @@ async def test_overview_maps_levels_and_serializes_high_priority() -> None:
 @pytest.mark.asyncio
 async def test_alert_page_returns_opaque_cursor() -> None:
     service = RiskQueryService(None, repository=FakeRepository())
+    query = RiskAlertPageQuery(limit=5)
 
-    result = await service.list_alerts(context(), RiskAlertPageQuery(limit=5))
+    result = await service.list_alerts(context(), query)
 
     assert result["has_more"] is True
-    assert decode_offset_cursor(result["next_cursor"]) == 5
+    binding = RiskQueryService._binding(context(), query)
+    assert decode_offset_cursor(result["next_cursor"], binding=binding) == 5
     assert result["items"][0]["rule_codes"] == ["RW-007"]
 
 
+def test_cursor_is_bound_to_user_and_filters() -> None:
+    """§3.8：游标绑定用户与查询条件，换个人或换个筛选条件都必须失效。"""
+    query = RiskAlertPageQuery(limit=5)
+    raw = encode_offset_cursor(5, binding=RiskQueryService._binding(context(), query))
+
+    assert decode_offset_cursor(raw, binding=RiskQueryService._binding(context(), query)) == 5
+
+    with pytest.raises(InvalidCursorError):
+        decode_offset_cursor(
+            raw,
+            binding=RiskQueryService._binding(context(user_id="990000003"), query),
+        )
+    with pytest.raises(InvalidCursorError):
+        other_filter = RiskAlertPageQuery(limit=5, keyword="张三")
+        decode_offset_cursor(
+            raw,
+            binding=RiskQueryService._binding(context(), other_filter),
+        )
+    # data_scope 收紧后旧游标同样失效
+    with pytest.raises(InvalidCursorError):
+        decode_offset_cursor(
+            raw,
+            binding=RiskQueryService._binding(
+                context(data_scope="own_customers", customer_ids=("9",)), query
+            ),
+        )
+
+
+def test_cursor_ignores_page_size_and_other_filters_do_not_collide() -> None:
+    """翻页时改 limit 不该让游标失效；不同证据类型之间不能互相串用游标。"""
+    base = RiskEvidencePageQuery(limit=10)
+    binding = RiskQueryService._binding(context(), base, "customers")
+
+    again = RiskQueryService._binding(context(), RiskEvidencePageQuery(limit=10), "customers")
+    other = RiskQueryService._binding(context(), RiskEvidencePageQuery(limit=10), "products")
+    assert binding == again
+    assert binding != other
+
+
 @pytest.mark.asyncio
 async def test_missing_alert_detail_is_hidden() -> None:
     service = RiskQueryService(None, repository=FakeRepository())