feat(kevin): reconcile Alpaca bracket auto-closes + order status

Bracket stop-loss/take-profit legs fill at Alpaca without passing through the executor, so those closes (and their P&L) were invisible locally.

- broker: add get_order(nested) + list_orders to BaseBroker/AlpacaBroker (+ SimulatedBroker); BrokerOrder carries child legs

- Trade gains broker_order_id (migration f6a7b8c9d0e1); executor stamps the entry order id

- new api_gateway trade-reconcile loop: books a closing SELL + realized P&L when a bracket leg fills (idempotent on the leg order id), syncs PENDING->terminal status, logs drift; runs alongside portfolio_sync

[ci skip]

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

shared/broker/base.py

@@ -9,7 +9,13 @@ changing strategy or execution logic.
 
 from abc import ABC, abstractmethod
 
-from shared.schemas.trading import AccountInfo, OrderRequest, OrderResult, PositionInfo
+from shared.schemas.trading import (
+    AccountInfo,
+    BrokerOrder,
+    OrderRequest,
+    OrderResult,
+    PositionInfo,
+)
 
 
 class BaseBroker(ABC):
@@ -85,3 +91,45 @@ class BaseBroker(ABC):
             Current state of the order including fill price if applicable.
         """
         ...
+
+    @abstractmethod
+    async def get_order(
+        self, order_id: str, *, nested: bool = True
+    ) -> BrokerOrder | None:
+        """Fetch an order including its bracket child legs.
+
+        Parameters
+        ----------
+        order_id:
+            The brokerage-assigned order identifier.
+        nested:
+            When ``True`` (the default), child legs (stop-loss / take-profit)
+            are populated on the returned :class:`BrokerOrder` so callers can
+            tell which leg filled and at what price.
+
+        Returns
+        -------
+        BrokerOrder | None
+            The order with its legs, or ``None`` if the order does not exist.
+        """
+        ...
+
+    @abstractmethod
+    async def list_orders(
+        self, *, status: str = "all", limit: int = 100
+    ) -> list[OrderResult]:
+        """List orders, optionally filtered by status.
+
+        Parameters
+        ----------
+        status:
+            One of ``"open"``, ``"closed"``, or ``"all"`` (the default).
+        limit:
+            Maximum number of orders to return.
+
+        Returns
+        -------
+        list[OrderResult]
+            One entry per matching order.
+        """
+        ...