fix: add copy_rates_from_pos_as_df fallback in fetch_latest_closed_rates_for_trading_client

Mt5DataClient (returned by create_trading_client) exposes copy_rates_from_pos_as_df,
not fetch_latest_rates_as_df. Adds a fallback path that resolves the granularity string
to an integer timeframe via parse_timeframe, fetches count+1 bars from start_pos=0,
and applies the same drop_forming_rate_bar + tail(count) logic so callers that use
the client returned by create_trading_client no longer need a compatibility shim.

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

mt5cli/trading.py

@@ -15,6 +15,7 @@ from .exceptions import Mt5OperationError
 from .history import drop_forming_rate_bar
 from .sdk import build_config
 from .utils import coerce_login as _coerce_login
+from .utils import parse_timeframe
 
 if TYPE_CHECKING:
     from collections.abc import Iterator, Mapping, Sequence
@@ -1625,10 +1626,17 @@ def fetch_latest_closed_rates_for_trading_client(
         msg = "count must be positive."
         raise ValueError(msg)
     fetch_method = getattr(client, "fetch_latest_rates_as_df", None)
-    if not callable(fetch_method):
+    copy_method = getattr(client, "copy_rates_from_pos_as_df", None)
+    if callable(fetch_method):
+        fetched = fetch_method(symbol, granularity, count + 1)
+    elif callable(copy_method):
+        timeframe = parse_timeframe(granularity)
+        fetched = copy_method(
+            symbol=symbol, timeframe=timeframe, start_pos=0, count=count + 1
+        )
+    else:
         msg = "MT5 trading client cannot fetch rate data."
         raise Mt5OperationError(msg)
-    fetched = fetch_method(symbol, granularity, count + 1)
     if not isinstance(fetched, pd.DataFrame):
         msg = (
             f"Malformed rate data for {symbol!r} at granularity {granularity!r}: "

tests/test_trading.py

@@ -3198,6 +3198,60 @@ class TestFetchLatestClosedRatesForTradingClient:
                 count=2,
             )
 
+    def test_copy_rates_from_pos_fallback_drops_forming_bar(self) -> None:
+        """Regression: client with only copy_rates_from_pos_as_df works end-to-end."""
+        client = MagicMock(spec=["copy_rates_from_pos_as_df"])
+        client.copy_rates_from_pos_as_df.return_value = pd.DataFrame(
+            {
+                "time": [1700000000, 1700000060, 1700000120],
+                "close": [1.0, 1.1, 1.2],
+            },
+        )
+
+        result = fetch_latest_closed_rates_for_trading_client(
+            client,
+            symbol="EURUSD",
+            granularity="M1",
+            count=2,
+        )
+
+        client.copy_rates_from_pos_as_df.assert_called_once_with(
+            symbol="EURUSD", timeframe=1, start_pos=0, count=3
+        )
+        assert list(result["close"]) == [1.0, 1.1]
+        assert list(result["time"]) == [1700000000, 1700000060]
+
+    def test_copy_rates_from_pos_fallback_resolves_granularity(self) -> None:
+        """Fallback path resolves granularity string to integer timeframe."""
+        client = MagicMock(spec=["copy_rates_from_pos_as_df"])
+        client.copy_rates_from_pos_as_df.return_value = pd.DataFrame(
+            {"time": [1, 2, 3, 4], "close": [1.0, 1.1, 1.2, 1.3]},
+        )
+
+        fetch_latest_closed_rates_for_trading_client(
+            client, symbol="USDJPY", granularity="H1", count=3
+        )
+
+        call_kwargs = client.copy_rates_from_pos_as_df.call_args.kwargs
+        assert call_kwargs["symbol"] == "USDJPY"
+        assert call_kwargs["timeframe"] == 16385
+        assert call_kwargs["start_pos"] == 0
+        assert call_kwargs["count"] == 4
+
+    def test_copy_rates_from_pos_fallback_returns_count_closed_rows(self) -> None:
+        """Fallback path trims to exactly count closed rows after forming-bar drop."""
+        client = MagicMock(spec=["copy_rates_from_pos_as_df"])
+        client.copy_rates_from_pos_as_df.return_value = pd.DataFrame(
+            {"time": list(range(6)), "close": [float(i) for i in range(6)]},
+        )
+
+        result = fetch_latest_closed_rates_for_trading_client(
+            client, symbol="EURUSD", granularity="M1", count=4
+        )
+
+        assert len(result) == 4
+        assert list(result["close"]) == [1.0, 2.0, 3.0, 4.0]
+
     def test_raises_when_trading_client_cannot_fetch_rates(self) -> None:
         """Test missing rate-fetch methods raise Mt5TradingError."""
         client = MagicMock(spec=[])
@@ -3528,6 +3582,29 @@ class TestFetchLatestClosedRatesIndexed:
         assert "close" in result.columns
         assert isinstance(result.index, pd.DatetimeIndex)
 
+    def test_copy_rates_from_pos_fallback_produces_utc_datetime_index(self) -> None:
+        """Fallback path via copy_rates_from_pos_as_df produces a UTC DatetimeIndex."""
+        client = MagicMock(spec=["copy_rates_from_pos_as_df"])
+        client.copy_rates_from_pos_as_df.return_value = pd.DataFrame(
+            {
+                "time": [1700000000, 1700003600, 1700007200],
+                "close": [1.1, 1.2, 1.3],
+            },
+        )
+
+        result = fetch_latest_closed_rates_indexed(
+            client,
+            symbol="EURUSD",
+            granularity="M1",
+            count=2,
+        )
+
+        assert isinstance(result.index, pd.DatetimeIndex)
+        assert result.index.name == "time"
+        assert str(result.index.tz) == "UTC"
+        assert "time" not in result.columns
+        assert list(result["close"]) == [1.1, 1.2]
+
 
 class TestExtractTickPrice:
     """Tests for the public extract_tick_price helper."""