fix: overseas order rt_cd check, limit price premium, paper cash fallback (#151)

Three fixes for overseas stock trading failures:

1. Price API exchange code mapping:
   - get_overseas_price() now applies _PRICE_EXCHANGE_MAP (NASD→NAS, NYSE→NYS, AMEX→AMS)
   - Price API HHDFS00000300 requires short exchange codes same as ranking API

2. rt_cd check in send_overseas_order():
   - Log WARNING (not INFO) when rt_cd != "0" (e.g., "주문가능금액이 부족합니다")
   - Caller (main.py) checks rt_cd == "0" before calling log_trade()
   - Prevents DB from recording failed orders as successful trades

3. Limit order price premium for BUY:
   - BUY limit price = current_price * 1.005 (0.5% premium)
   - SELL limit price = current_price (no premium)
   - Improves fill probability: KIS VTS only accepts limit orders,
     and last price is typically at or below ask

4. PAPER_OVERSEAS_CASH fallback (config + main.py):
   - New setting: PAPER_OVERSEAS_CASH = 50000.0 (USD)
   - When VTS overseas balance API fails/returns 0, use this as simulated cash
   - Applied in both trading_cycle() and run_daily_session()

5. Candidate price fallback:
   - If price API returns 0, use scanner candidate price as fallback

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_overseas_broker.py

@@ -8,7 +8,7 @@ import aiohttp
 import pytest
 
 from src.broker.kis_api import KISBroker
-from src.broker.overseas import OverseasBroker, _RANKING_EXCHANGE_MAP
+from src.broker.overseas import OverseasBroker, _PRICE_EXCHANGE_MAP, _RANKING_EXCHANGE_MAP
 from src.config import Settings
 
 
@@ -302,7 +302,7 @@ class TestGetOverseasPrice:
 
         call_args = mock_session.get.call_args
         params = call_args[1]["params"]
-        assert params["EXCD"] == "NASD"
+        assert params["EXCD"] == "NAS"  # NASD → NAS via _PRICE_EXCHANGE_MAP
         assert params["SYMB"] == "AAPL"
 
     @pytest.mark.asyncio
@@ -519,3 +519,125 @@ class TestExtractRankingRows:
     def test_filters_non_dict_rows(self, overseas_broker: OverseasBroker) -> None:
         data = {"output": [{"a": 1}, "invalid", {"b": 2}]}
         assert overseas_broker._extract_ranking_rows(data) == [{"a": 1}, {"b": 2}]
+
+
+class TestPriceExchangeMap:
+    """Test _PRICE_EXCHANGE_MAP is applied in get_overseas_price (issue #151)."""
+
+    def test_price_map_equals_ranking_map(self) -> None:
+        assert _PRICE_EXCHANGE_MAP is _RANKING_EXCHANGE_MAP
+
+    @pytest.mark.parametrize("original,expected", [
+        ("NASD", "NAS"),
+        ("NYSE", "NYS"),
+        ("AMEX", "AMS"),
+    ])
+    def test_us_exchange_code_mapping(self, original: str, expected: str) -> None:
+        assert _PRICE_EXCHANGE_MAP[original] == expected
+
+    @pytest.mark.asyncio
+    async def test_get_overseas_price_sends_mapped_code(
+        self, overseas_broker: OverseasBroker
+    ) -> None:
+        """NASD → NAS must be sent to HHDFS00000300."""
+        mock_resp = AsyncMock()
+        mock_resp.status = 200
+        mock_resp.json = AsyncMock(return_value={"output": {"last": "200.00"}})
+
+        mock_session = MagicMock()
+        mock_session.get = MagicMock(return_value=_make_async_cm(mock_resp))
+        _setup_broker_mocks(overseas_broker, mock_session)
+
+        await overseas_broker.get_overseas_price("NASD", "AAPL")
+
+        params = mock_session.get.call_args[1]["params"]
+        assert params["EXCD"] == "NAS"
+
+
+class TestOrderRtCdCheck:
+    """Test that send_overseas_order checks rt_cd and logs accordingly (issue #151)."""
+
+    @pytest.fixture
+    def overseas_broker(self, mock_settings: Settings) -> OverseasBroker:
+        broker = MagicMock(spec=KISBroker)
+        broker._settings = mock_settings
+        broker._account_no = "12345678"
+        broker._product_cd = "01"
+        broker._base_url = "https://openapivts.koreainvestment.com:9443"
+        broker._rate_limiter = AsyncMock()
+        broker._rate_limiter.acquire = AsyncMock()
+        broker._auth_headers = AsyncMock(return_value={"authorization": "Bearer t"})
+        broker._get_hash_key = AsyncMock(return_value="hashval")
+        return OverseasBroker(broker)
+
+    @pytest.mark.asyncio
+    async def test_success_rt_cd_returns_data(
+        self, overseas_broker: OverseasBroker
+    ) -> None:
+        """rt_cd='0' → order accepted, data returned."""
+        mock_resp = AsyncMock()
+        mock_resp.status = 200
+        mock_resp.json = AsyncMock(return_value={"rt_cd": "0", "msg1": "완료"})
+
+        mock_session = MagicMock()
+        mock_session.post = MagicMock(return_value=_make_async_cm(mock_resp))
+        overseas_broker._broker._get_session = MagicMock(return_value=mock_session)
+
+        result = await overseas_broker.send_overseas_order("NASD", "AAPL", "BUY", 10, price=150.0)
+        assert result["rt_cd"] == "0"
+
+    @pytest.mark.asyncio
+    async def test_error_rt_cd_returns_data_with_msg(
+        self, overseas_broker: OverseasBroker
+    ) -> None:
+        """rt_cd != '0' → order rejected, data still returned (caller checks rt_cd)."""
+        mock_resp = AsyncMock()
+        mock_resp.status = 200
+        mock_resp.json = AsyncMock(
+            return_value={"rt_cd": "1", "msg1": "주문가능금액이 부족합니다."}
+        )
+
+        mock_session = MagicMock()
+        mock_session.post = MagicMock(return_value=_make_async_cm(mock_resp))
+        overseas_broker._broker._get_session = MagicMock(return_value=mock_session)
+
+        result = await overseas_broker.send_overseas_order("NASD", "AAPL", "BUY", 10, price=150.0)
+        assert result["rt_cd"] == "1"
+        assert "부족" in result["msg1"]
+
+
+class TestPaperOverseasCash:
+    """Test PAPER_OVERSEAS_CASH config setting (issue #151)."""
+
+    def test_default_value(self) -> None:
+        settings = Settings(
+            KIS_APP_KEY="k",
+            KIS_APP_SECRET="s",
+            KIS_ACCOUNT_NO="12345678-01",
+            GEMINI_API_KEY="g",
+        )
+        assert settings.PAPER_OVERSEAS_CASH == 50000.0
+
+    def test_env_override(self) -> None:
+        import os
+        os.environ["PAPER_OVERSEAS_CASH"] = "25000"
+        settings = Settings(
+            KIS_APP_KEY="k",
+            KIS_APP_SECRET="s",
+            KIS_ACCOUNT_NO="12345678-01",
+            GEMINI_API_KEY="g",
+        )
+        assert settings.PAPER_OVERSEAS_CASH == 25000.0
+        del os.environ["PAPER_OVERSEAS_CASH"]
+
+    def test_zero_disables_fallback(self) -> None:
+        import os
+        os.environ["PAPER_OVERSEAS_CASH"] = "0"
+        settings = Settings(
+            KIS_APP_KEY="k",
+            KIS_APP_SECRET="s",
+            KIS_ACCOUNT_NO="12345678-01",
+            GEMINI_API_KEY="g",
+        )
+        assert settings.PAPER_OVERSEAS_CASH == 0.0
+        del os.environ["PAPER_OVERSEAS_CASH"]