fix(dupont): reject out-of-domain window + bidirectional clip + suffix discipline (R1-R4/M2)

Per finance ruling 2026-10-05 (project-20261005-dupont-oob-window-fix):

- R1: no intersection with available month domain => explicit error (endpoint 400), no window fields

- R2: with intersection => intersection window, months>=1 (kills inversion and months<=0)

- R3: quarter/half/... suffix kept only when returned window == nominal window (clipped flag)

- R4: symmetric lower-bound clip note; M2: TTM nominal window = [anchor-11, anchor] (12 months)

- M1: docstring correction (lower-bound overflow is clipped, not 400)

No push / no deploy / no restart / no DB write.

backend/app/api/reports.py

@@ -23,7 +23,7 @@ from app.utils.deviation_engine import calc_period_deviation, calc_period_diff,
 from app.utils.alert_entity_scope import month_period_clause
 from app.utils.profitability_params import load_profitability_params
 from app.utils.dupont_basis import (
-    annualize_factors, available_months, build_window_meta, check_identity,
+    annualize_factors, apply_period_suffix, available_months, build_window_meta, check_identity,
     compute_factors, latest_stock_month, load_dupont_params, months_between, prev_month,
     resolve_window, stock_balance, sum_flows,
 )
@@ -2330,9 +2330,9 @@ def get_dupont_analysis(
     name_row = db.execute(
         text("SELECT name FROM entities WHERE id = :eid"), {"eid": entity_id}).first()
     entity_name = (name_row[0] if name_row else None) or ("陕西酣客文化传媒" if slug == "hanke" else "陕西博海网络科技")
-    suffix = {"ytd": "（YTD 年初至今）", "ttm": "（TTM 滚动 12 月）", "month": "（单月）",
-              "quarter": "（季度）", "half": "（半年）", "year": "（全年）", "custom": "（自定义区间）"}
-    label = win["label"] + suffix.get(win["period_key"], "")
+    # R3 后缀纪律：仅在「返回窗口 == 名义窗口」（未裁剪）时保留「（季度）/（半年）…」后缀；
+    # 发生任何裁剪 ⇒ 去后缀，period = 实际窗口标签（判据由 resolve_window 回传 `clipped`）。
+    label = apply_period_suffix(win["label"], win["period_key"], bool(win.get("clipped")))
 
     cur = _dupont_window_values(db, entity_id, caliber, win["period_start"], win["period_end"])
     ann = annualize_factors(dict(cur["factors"]), win["months"], annualize)