fix(fundamentals): 换报告期公告当日不再丢失上一期财务因子值

attach_fundamental_factors 用公告日做 asof 回看再按「严格大于」门控:
日期正好等于新一期公告日时, join_asof 已匹配到「当天还不能用」的新记录,
门控随即置 null, 打断上一期的前向填充。矩阵路径 build_fundamental_matrices
按 searchsorted(side="right") 逐期覆盖, 公告当日保留上一期, 两条路径因此不一致
(其 docstring 声明与 attach_fundamental_factors 同口径)。

asof 键改用生效日 (公告日次日), 只命中已生效的报告期; 公告前仍为 null 的门控不变。
补 tests/test_fundamental_factors.py 的两条公告一致性用例。

backend/app/backtest/fundamentals.py

@@ -103,11 +103,18 @@ def attach_fundamental_factors(
     columns = sorted(
         {FUNDAMENTAL_FACTORS[name]["column"] for name in missing_columns}
     )
-    right = snapshot.select(["symbol", "_announce", *columns]).sort(["symbol", "_announce"])
+    # asof 键取生效日 (公告日次日) 而非公告日: 直接用公告日回看会在换报告期的
+    # 公告当日取到「尚未生效」的新一期并被门控置 null, 打断上一期的前向填充,
+    # 与矩阵路径 (searchsorted side="right") 不一致。
+    right = (
+        snapshot.select(["symbol", "_announce", *columns])
+        .with_columns(pl.col("_announce").dt.offset_by("1d").alias("_effective"))
+        .sort(["symbol", "_effective"])
+    )
     joined = panel.join_asof(
         right,
         left_on="date",
-        right_on="_announce",
+        right_on="_effective",
         by="symbol",
         strategy="backward",
         check_sortedness=False,  # 双侧均已按 (symbol, key) 排序, 免除逐组检查开销
@@ -128,7 +135,7 @@ def attach_fundamental_factors(
         expressions.append(
             pl.when(announced).then(value).otherwise(None).alias(name)
         )
-    return joined.with_columns(expressions)
+    return joined.with_columns(expressions).drop("_effective")
 
 
 def build_fundamental_matrices(

backend/tests/test_fundamental_factors.py

@@ -85,7 +85,7 @@ def test_attach_replaces_with_newer_announcement():
     assert roe[4] is None            # 4-5 公告日
     assert roe[5] == 20.0            # 4-6 起 20.0
     assert roe[13] == 20.0           # 4-14
-    assert roe[14] is None           # 4-15 二次公告日, 当天仍不可用 (严格大于)
+    assert roe[14] == 20.0           # 4-15 二次公告日: 新一期尚未生效, 仍保留上一期
     assert roe[15] == 33.0           # 4-16 起新公告生效
 
 
@@ -121,6 +121,25 @@ def test_matrix_field_matches_polars_attach():
                 np.testing.assert_allclose(actual, expected, rtol=1e-6)
 
 
+def test_matrix_field_matches_polars_attach_across_two_announcements():
+    """换报告期时两条路径仍须一致: 新公告当日应保留上一期值(前向填充不断档)。"""
+    panel = _daily_panel(date(2026, 4, 1), 20, ("600000.SH",))
+    snapshot = _snapshot_frame([
+        {"symbol": "600000.SH", "announce": "2026-04-05", "roe": 20.0},
+        {"symbol": "600000.SH", "announce": "2026-04-15", "roe": 33.0},
+    ])
+    attached = attach_fundamental_factors(panel, snapshot, ["roe_latest"]).sort("date")
+    market = build_market_data_matrix(panel)
+    matrix = build_fundamental_matrices(market, snapshot, ["roe_latest"])["roe_latest"]
+    column = market.symbols.index("600000.SH")
+    for row_index, value in enumerate(attached["roe_latest"].to_list()):
+        actual = matrix[row_index, column]
+        if value is None:
+            assert np.isnan(actual), (row_index, actual)
+        else:
+            np.testing.assert_allclose(actual, value, rtol=1e-6)
+
+
 def test_bps_nonpositive_gives_null_pb():
     panel = _daily_panel(date(2026, 4, 1), 8, ("000001.SZ",))
     snapshot = _snapshot_frame([