Restore hold_timing open-position unit test.

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

backend/tests/test_hold_timing.py

@@ -55,6 +55,14 @@ def test_hold_dual_leg_uses_group_close():
     assert h["hold_basis"] == "group"
 
 
+def test_hold_open_no_close():
+    g = {"open_at_ms": 100, "close_at_ms": None, "status": "open", "close_reason": None}
+    h = hold_timing(g, [])
+    assert h["hold_close_at_ms"] is None
+    assert h["hold_ms"] is None
+    assert h["hold_basis"] == "open"
+
+
 def test_hold_sqlite_row_like_without_get():
     """sqlite3.Row 无 .get，需能转 dict。"""