Add risk leverage basis option: actual ask vs selection leverage.

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

backend/tests/test_risk_sizing.py

@@ -8,6 +8,8 @@ from app.strategy.risk_sizing import (
     BASE_PERP_ETH,
     compute_k,
     floor_k_1dp,
+    normalize_risk_leverage_basis,
+    resolve_sizing_option_ask,
     unit_cost,
 )
 
@@ -78,3 +80,72 @@ def test_compute_k_too_small() -> None:
 
 def test_unit_cost() -> None:
     assert abs(unit_cost(index_px=2000, option_ask=20, fee_rate=0.0005) - 43.0) < 1e-9
+
+
+def test_normalize_risk_leverage_basis() -> None:
+    assert normalize_risk_leverage_basis("actual") == "actual"
+    assert normalize_risk_leverage_basis("selection") == "selection"
+    assert normalize_risk_leverage_basis("min_option_leverage") == "selection"
+    assert normalize_risk_leverage_basis("weird", default="selection") == "selection"
+
+
+def test_resolve_sizing_ask_selection_vs_actual() -> None:
+    # 指数 2000、选约杠杆 100 → 隐含卖一 20；实际卖一更便宜 10
+    sel_ask, basis = resolve_sizing_option_ask(
+        index_px=2000.0,
+        option_ask=10.0,
+        leverage_basis="selection",
+        min_option_leverage=100.0,
+    )
+    assert basis == "selection"
+    assert abs(sel_ask - 20.0) < 1e-9
+
+    act_ask, basis2 = resolve_sizing_option_ask(
+        index_px=2000.0,
+        option_ask=10.0,
+        leverage_basis="actual",
+        min_option_leverage=100.0,
+    )
+    assert basis2 == "actual"
+    assert abs(act_ask - 10.0) < 1e-9
+
+
+def test_selection_basis_yields_smaller_k_when_ask_cheap() -> None:
+    # 预算 43：选约隐含 ask=20 → k=1；若用实际 ask=10 → 单位成本更小 → k 更大
+    r_sel = compute_k(budget=43.0, index_px=2000.0, option_ask=20.0, fee_rate=0.0005)
+    r_act = compute_k(budget=43.0, index_px=2000.0, option_ask=10.0, fee_rate=0.0005)
+    assert r_sel.ok and r_act.ok
+    assert r_sel.k == 1.0
+    assert r_act.k is not None and r_act.k > r_sel.k
+
+
+def test_compute_risk_sizing_respects_basis(tmp_path, monkeypatch) -> None:
+    monkeypatch.setenv("MODE", "SIM")
+    from app.models.db import Database
+    from app.strategy.risk_sizing import compute_risk_sizing
+
+    db = Database(tmp_path / "risk_basis.db")
+    db.set_setting("sizing_mode", "risk_based")
+    db.set_setting("risk_loss_mode", "absolute")
+    db.set_setting("risk_loss_usdt", "43")
+    db.set_setting("fee_rate", "0.0005")
+    db.set_setting("min_option_leverage", "100")
+    db.set_setting("risk_perp_unit", "1")
+    db.set_setting("risk_option_unit", "2")
+    db.set_setting("risk_exit_unit", "15")
+
+    db.set_setting("risk_leverage_basis", "selection")
+    r1 = compute_risk_sizing(index_px=2000.0, option_ask=10.0, db=db)
+    assert r1.ok
+    assert r1.leverage_basis == "selection"
+    assert r1.k == 1.0
+    assert r1.actual_option_ask == 10.0
+    assert r1.option_ask == 20.0
+
+    db.set_setting("risk_leverage_basis", "actual")
+    r2 = compute_risk_sizing(index_px=2000.0, option_ask=10.0, db=db)
+    assert r2.ok
+    assert r2.leverage_basis == "actual"
+    assert r2.k is not None and r2.k > 1.0
+    assert r2.option_ask == 10.0
+    db.close()