feat: Implement idempotency and recovery mechanisms for order execution

- Add IdempotencyKeyFactory for generating unique user references based on execution legs.
- Introduce OrderReconciler to reconcile order statuses with historical data.
- Implement PartialFillRecovery to handle partial fills by canceling orders and placing hedges.
- Create TriangularExecutionSequencer for executing triangular arbitrage strategies.
- Enhance storage with new tables for trades, orders, and PnL events.
- Develop AsyncExecutionWriter for asynchronous writing of execution records to the database.
- Add unit tests for execution persistence, sequencer behavior, fill monitoring, and idempotency checks.
- Update KrakenRestClient to ensure proper payloads for order placement and querying.

tests/unit/test_idempotency.py

@@ -0,0 +1,109 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from datetime import UTC, datetime
+from typing import Any
+
+import pytest
+
+from arbitrade.detection.engine import OpportunityEvent
+from arbitrade.execution.idempotency import IdempotencyKeyFactory, OrderReconciler
+from arbitrade.execution.sequencer import ExecutionLeg
+
+
+@dataclass(slots=True)
+class _FakeHistoryClient:
+    response: dict[str, Any]
+
+    async def query_order(self, *, order_id: str, include_trades: bool = True) -> dict[str, Any]:
+        return self.response
+
+
+def _sample_event() -> OpportunityEvent:
+    return OpportunityEvent(
+        detected_at=datetime.now(UTC),
+        cycle="USD->BTC->ETH->USD",
+        updated_pair="BTC/USD",
+        gross_rate=1.02,
+        net_rate=1.01,
+        gross_pct=2.0,
+        net_pct=1.0,
+        est_profit=1.0,
+        allocated_capital=10.0,
+    )
+
+
+def test_idempotency_key_factory_is_deterministic() -> None:
+    factory = IdempotencyKeyFactory()
+    event = _sample_event()
+    leg = ExecutionLeg(
+        from_currency="USD",
+        to_currency="BTC",
+        pair="BTC/USD",
+        side="buy",
+        volume=10.0,
+    )
+
+    first = factory.user_ref_for_leg(event, leg, 0)
+    second = factory.user_ref_for_leg(event, leg, 0)
+
+    assert first == second
+    assert first > 0
+
+
+@pytest.mark.asyncio
+async def test_order_reconciler_maps_query_response_to_report() -> None:
+    client = _FakeHistoryClient(
+        response={
+            "order-1": {
+                "status": "closed",
+                "vol_exec": "5.0",
+                "price": "100.0",
+                "pair": "BTC/USD",
+                "type": "buy",
+                "userref": 12345,
+            }
+        }
+    )
+    reconciler = OrderReconciler(client)
+
+    report = await reconciler.reconcile_order(
+        order_id="order-1",
+        user_ref=12345,
+        expected_pair="BTC/USD",
+        expected_side="buy",
+        expected_volume=10.0,
+    )
+
+    assert report.is_terminal
+    assert report.matches_request
+    assert report.status == "closed"
+    assert report.filled_volume == 5.0
+    assert report.avg_price == 100.0
+
+
+@pytest.mark.asyncio
+async def test_order_reconciler_marks_mismatch() -> None:
+    client = _FakeHistoryClient(
+        response={
+            "order-1": {
+                "status": "closed",
+                "vol_exec": "5.0",
+                "price": "100.0",
+                "pair": "ETH/USD",
+                "type": "sell",
+                "userref": 999,
+            }
+        }
+    )
+    reconciler = OrderReconciler(client)
+
+    report = await reconciler.reconcile_order(
+        order_id="order-1",
+        user_ref=12345,
+        expected_pair="BTC/USD",
+        expected_side="buy",
+        expected_volume=10.0,
+    )
+
+    assert not report.matches_request