refactor(V2): IBKR client — remove dead whitelist + max_cycles test

Code review polish (commit b9c58a3):
- Remove unused _AUTO_CONFIRM_WHITELIST (was scaffolding, never wired)
- Replace with policy comment documenting auto-confirm behavior
- New test: test_place_order_too_many_confirmations

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/unit/exchanges/ibkr/test_client.py

@@ -205,3 +205,28 @@ async def test_cancel_order(httpx_mock: HTTPXMock, client):
     )
     res = await client.cancel_order("OID42")
     assert res["canceled"] is True
+
+
+@pytest.mark.asyncio
+async def test_place_order_too_many_confirmations(httpx_mock: HTTPXMock, client):
+    httpx_mock.add_response(url=re.compile(r".*/tickle"), json={})
+    httpx_mock.add_response(
+        url=re.compile(r".*/trsrv/secdef/search"),
+        json=[{"conid": 265598, "symbol": "AAPL", "secType": "STK"}],
+    )
+    # Initial place + 3 reply cycles all return new warnings — should fail at MAX_CYCLES
+    httpx_mock.add_response(
+        url=re.compile(r".*/iserver/account/DU1234/orders$"),
+        method="POST",
+        json=[{"id": "msg1", "message": ["outside RTH"]}],
+    )
+    for n in range(2, 5):
+        httpx_mock.add_response(
+            url=re.compile(rf".*/iserver/reply/msg{n-1}$"),
+            method="POST",
+            json=[{"id": f"msg{n}", "message": ["outside RTH"]}],
+        )
+    with pytest.raises(IBKRError, match="IBKR_ORDER_TOO_MANY_CONFIRMATIONS"):
+        await client.place_order(
+            symbol="AAPL", side="buy", qty=1, order_type="market",
+        )