fix(trend): correct DCA triggers and partial-position PnL across exchanges

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_trend_dca_pnl.py

@@ -0,0 +1,37 @@
+"""趋势回调：补仓触达与有效保证金估算。"""
+from strategy_trend_lib import trend_dca_level_reached, trend_effective_margin_capital
+
+
+def test_trend_dca_short_monotonic_up_fills_missed_legs():
+    """做空价升：旧逻辑需 last<level，价越过 0.3437 后 last 已高于该档则永不补仓。"""
+    direction = "short"
+    levels = [0.3413, 0.3437, 0.346, 0.3483, 0.3507]
+    pf = 0.353
+    filled = [lv for lv in levels if trend_dca_level_reached(direction, pf, lv)]
+    assert filled == levels
+
+
+def test_trend_dca_short_not_before_first_level():
+    direction = "short"
+    assert not trend_dca_level_reached(direction, 0.336, 0.3413)
+    assert trend_dca_level_reached(direction, 0.3413, 0.3413)
+
+
+def test_trend_effective_margin_first_leg_only():
+    plan = {
+        "plan_margin_capital": 12.11,
+        "target_order_amount": 359.0,
+        "order_amount_open": 179.0,
+        "first_order_amount": 179.0,
+    }
+    m = trend_effective_margin_capital(plan)
+    assert abs(m - 12.11 * 179 / 359) < 0.01
+
+
+def test_trend_effective_margin_full_position():
+    plan = {
+        "plan_margin_capital": 12.11,
+        "target_order_amount": 359.0,
+        "order_amount_open": 359.0,
+    }
+    assert trend_effective_margin_capital(plan) == 12.11