feat: add session-aware order policy guard for low-liquidity market-order rejection (#279)

src/core/order_policy.py

@@ -0,0 +1,93 @@
+"""Session-aware order policy guards.
+
+Default policy:
+- Low-liquidity sessions must reject market orders (price <= 0).
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from datetime import UTC, datetime, time
+from zoneinfo import ZoneInfo
+
+from src.markets.schedule import MarketInfo
+
+_LOW_LIQUIDITY_SESSIONS = {"NXT_AFTER", "US_PRE", "US_DAY", "US_AFTER"}
+
+
+class OrderPolicyRejected(Exception):
+    """Raised when an order violates session policy."""
+
+    def __init__(self, message: str, *, session_id: str, market_code: str) -> None:
+        super().__init__(message)
+        self.session_id = session_id
+        self.market_code = market_code
+
+
+@dataclass(frozen=True)
+class SessionInfo:
+    session_id: str
+    is_low_liquidity: bool
+
+
+def classify_session_id(market: MarketInfo, now: datetime | None = None) -> str:
+    """Classify current session by KST schedule used in v3 docs."""
+    now = now or datetime.now(UTC)
+    # v3 session tables are explicitly defined in KST perspective.
+    kst_time = now.astimezone(ZoneInfo("Asia/Seoul")).timetz().replace(tzinfo=None)
+
+    if market.code == "KR":
+        if time(8, 0) <= kst_time < time(8, 50):
+            return "NXT_PRE"
+        if time(9, 0) <= kst_time < time(15, 30):
+            return "KRX_REG"
+        if time(15, 30) <= kst_time < time(20, 0):
+            return "NXT_AFTER"
+        return "KR_OFF"
+
+    if market.code.startswith("US"):
+        if time(10, 0) <= kst_time < time(18, 0):
+            return "US_DAY"
+        if time(18, 0) <= kst_time < time(23, 30):
+            return "US_PRE"
+        if time(23, 30) <= kst_time or kst_time < time(6, 0):
+            return "US_REG"
+        if time(6, 0) <= kst_time < time(7, 0):
+            return "US_AFTER"
+        return "US_OFF"
+
+    return "GENERIC_REG"
+
+
+def get_session_info(market: MarketInfo, now: datetime | None = None) -> SessionInfo:
+    session_id = classify_session_id(market, now)
+    return SessionInfo(session_id=session_id, is_low_liquidity=session_id in _LOW_LIQUIDITY_SESSIONS)
+
+
+def validate_order_policy(
+    *,
+    market: MarketInfo,
+    order_type: str,
+    price: float,
+    now: datetime | None = None,
+) -> SessionInfo:
+    """Validate order against session policy and return resolved session info."""
+    info = get_session_info(market, now)
+
+    is_market_order = price <= 0
+    if info.is_low_liquidity and is_market_order:
+        raise OrderPolicyRejected(
+            f"Market order is forbidden in low-liquidity session ({info.session_id})",
+            session_id=info.session_id,
+            market_code=market.code,
+        )
+
+    # Guard against accidental unsupported actions.
+    if order_type not in {"BUY", "SELL"}:
+        raise OrderPolicyRejected(
+            f"Unsupported order_type={order_type}",
+            session_id=info.session_id,
+            market_code=market.code,
+        )
+
+    return info