Add fixed-direction switch for perp/option open side.

When enabled, lock perp long→buy Put or short→buy Call with ITM/ATM only; off keeps ATM/ask rules.

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

backend/app/strategy/signal.py

@@ -66,3 +66,38 @@ def decide(
             put_ask=pa,
         )
     return None
+
+
+def decide_fixed(
+    call_ask: float | None,
+    put_ask: float | None,
+    *,
+    perp_side: str,
+) -> Signal | None:
+    """
+    固定方向：
+    - 永续多 → 买 Put
+    - 永续空 → 买 Call
+    """
+    if call_ask is None or put_ask is None:
+        return None
+    side = (perp_side or "").strip().lower()
+    ca = float(call_ask)
+    pa = float(put_ask)
+    if side == "long":
+        return Signal(
+            bias="fixed_long_put",
+            option_side="put",
+            perp_side="long",
+            call_ask=ca,
+            put_ask=pa,
+        )
+    if side == "short":
+        return Signal(
+            bias="fixed_short_call",
+            option_side="call",
+            perp_side="short",
+            call_ask=ca,
+            put_ask=pa,
+        )
+    return None