fix: merge US stock 3m bars returned by the Yahoo chart

backend_api_python/app/data_sources/us_stock.py

@@ -505,6 +505,8 @@ def get_kline(
 
 
             klines = self._fetch_yahoo_chart(symbol, interval, start_date, end_date, effective_limit)
+            if klines and merge_factor > 1:
+                klines = self._merge_every_n_sorted_bars(klines, merge_factor)
             if not klines:
                 if timeframe in ('1m', '3m', '5m', '15m', '30m', '1H', '4H'):
                     # Nasdaq's intraday chart is a latest-session feed, not a

backend_api_python/tests/test_us_stock_intraday_window.py

@@ -85,3 +85,47 @@ def history(self, **kwargs):
 
     assert captured["start"] == start
     assert captured["end"] == end
+
+
+class _MinuteChartResponse:
+    def __init__(self, start_ts, count):
+        self._timestamps = [start_ts + 60 * i for i in range(count)]
+
+    def raise_for_status(self):
+        return None
+
+    def json(self):
+        n = len(self._timestamps)
+        return {"chart": {"result": [{
+            "timestamp": self._timestamps,
+            "indicators": {"quote": [{
+                "open": [100.0 + i for i in range(n)],
+                "high": [101.0 + i for i in range(n)],
+                "low": [99.0 + i for i in range(n)],
+                "close": [100.5 + i for i in range(n)],
+                "volume": [10] * n,
+            }]},
+        }]}}
+
+
+def test_three_minute_klines_from_yahoo_chart_are_merged(monkeypatch):
+    session_open = int(datetime(2026, 9, 14, 13, 30).timestamp())
+    captured = {}
+
+    def fake_get(_url, **kwargs):
+        captured.update(kwargs["params"])
+        return _MinuteChartResponse(session_open, 6)
+
+    monkeypatch.setattr(us_stock.requests, "get", fake_get)
+    source = USStockDataSource.__new__(USStockDataSource)
+
+    bars = source.get_kline("NVDA", "3m", 2, before_time=session_open + 3600)
+
+    assert captured["interval"] == "1m"
+    assert [bar["time"] for bar in bars] == [session_open, session_open + 180]
+    assert bars[0]["open"] == 100.0
+    assert bars[0]["high"] == 103.0
+    assert bars[0]["low"] == 99.0
+    assert bars[0]["close"] == 102.5
+    assert bars[0]["volume"] == 30
+    assert bars[1]["close"] == 105.5