fix(data): respect the configured vendor chain and log vendor failures

The router silently extended every request to all available vendors regardless
of config, so an explicit single-vendor choice still fell back to others and
returned data from an unexpected source (#988, #289), and serious primary-vendor
errors were swallowed without a trace (#989). The configured vendor list is now
the exact chain (list several for ordered fallback; "default" uses all), unknown
vendors raise, and swallowed vendor errors are logged. Adds an autouse config
isolation fixture so vendor config can't leak between tests.

tests/conftest.py

@@ -35,6 +35,25 @@ def _dummy_api_keys(monkeypatch):
         monkeypatch.setenv(env_var, os.environ.get(env_var, "placeholder"))
 
 
+@pytest.fixture(autouse=True)
+def _isolate_config():
+    """Reset the global dataflows config before and after each test.
+
+    ``set_config`` merges (it never clears keys absent from the override), so a
+    test that sets e.g. ``tool_vendors`` would otherwise leak into later tests
+    and make routing behavior order-dependent. Replace the global outright so
+    every test starts from a clean DEFAULT_CONFIG.
+    """
+    import copy
+
+    import tradingagents.dataflows.config as config_module
+    import tradingagents.default_config as default_config
+
+    config_module._config = copy.deepcopy(default_config.DEFAULT_CONFIG)
+    yield
+    config_module._config = copy.deepcopy(default_config.DEFAULT_CONFIG)
+
+
 @pytest.fixture()
 def mock_llm_client():
     client = MagicMock()

tests/test_vendor_routing.py

@@ -0,0 +1,102 @@
+"""Vendor router must respect the configured chain and never silently hide a
+broken primary.
+
+Regressions for #988 (explicit single-vendor config still fell back to others),
+#289 (fallback ran for unchosen vendors), and #989 (serious primary failures
+were swallowed without a trace).
+"""
+import copy
+import logging
+import unittest
+from unittest import mock
+
+import pytest
+
+import tradingagents.dataflows.config as config_module
+import tradingagents.default_config as default_config
+from tradingagents.dataflows import interface
+from tradingagents.dataflows.config import set_config
+from tradingagents.dataflows.symbol_utils import NoMarketDataError
+
+
+def _reset_config():
+    # Hard reset: set_config() merges, so empty DEFAULT dicts (e.g. tool_vendors)
+    # don't clear keys leaked by other tests. Replace the global outright.
+    config_module._config = copy.deepcopy(default_config.DEFAULT_CONFIG)
+
+
+def _no_data(symbol, *a, **k):
+    raise NoMarketDataError(symbol, symbol, "no rows")
+
+
+def _returns(value):
+    def impl(symbol, *a, **k):
+        return value
+    return impl
+
+
+def _raises(exc):
+    def impl(symbol, *a, **k):
+        raise exc
+    return impl
+
+
+@pytest.mark.unit
+class VendorRoutingTests(unittest.TestCase):
+    def setUp(self):
+        _reset_config()
+
+    def tearDown(self):
+        _reset_config()
+
+    def _route(self, vendors_for_get_stock_data):
+        return mock.patch.dict(
+            interface.VENDOR_METHODS,
+            {"get_stock_data": vendors_for_get_stock_data},
+            clear=False,
+        )
+
+    def test_explicit_single_vendor_does_not_fall_back(self):
+        # #988: with yfinance pinned, a healthy alpha_vantage must NOT be used.
+        set_config({"data_vendors": {"core_stock_apis": "yfinance"}})
+        av = mock.Mock(side_effect=_returns("AV_DATA"))
+        with self._route({"yfinance": _no_data, "alpha_vantage": av}):
+            result = interface.route_to_vendor("get_stock_data", "FAKE", "2026-01-01", "2026-01-10")
+        self.assertIn("NO_DATA_AVAILABLE", result)
+        av.assert_not_called()  # the unchosen vendor was never tried
+
+    def test_explicit_multi_vendor_falls_back_within_chain(self):
+        # Listing both vendors opts in to ordered fallback.
+        set_config({"data_vendors": {"core_stock_apis": "yfinance,alpha_vantage"}})
+        with self._route({"yfinance": _no_data, "alpha_vantage": _returns("AV_DATA")}):
+            result = interface.route_to_vendor("get_stock_data", "AAPL", "2026-01-01", "2026-01-10")
+        self.assertEqual(result, "AV_DATA")
+
+    def test_primary_error_is_logged_not_masked(self):
+        # #989: primary errors + fallback no-data -> NO_DATA, but the failure
+        # must be visible in logs (broken primary not hidden).
+        set_config({"data_vendors": {"core_stock_apis": "yfinance,alpha_vantage"}})
+        with self._route({"yfinance": _raises(ValueError("boom")), "alpha_vantage": _no_data}):
+            with self.assertLogs("tradingagents.dataflows.interface", level="WARNING") as cm:
+                result = interface.route_to_vendor("get_stock_data", "AAPL", "2026-01-01", "2026-01-10")
+        self.assertIn("NO_DATA_AVAILABLE", result)
+        joined = "\n".join(cm.output)
+        self.assertIn("boom", joined)            # the real error surfaced in logs
+        self.assertIn("yfinance", joined)
+
+    def test_unknown_configured_vendor_raises(self):
+        set_config({"data_vendors": {"core_stock_apis": "bogus_vendor"}})
+        with self.assertRaises(ValueError) as ctx:
+            interface.route_to_vendor("get_stock_data", "AAPL", "2026-01-01", "2026-01-10")
+        self.assertIn("bogus_vendor", str(ctx.exception))
+
+    def test_default_sentinel_uses_all_vendors(self):
+        # No explicit choice ("default") keeps the resilient full-chain behavior.
+        set_config({"data_vendors": {"core_stock_apis": "default"}})
+        with self._route({"yfinance": _no_data, "alpha_vantage": _returns("AV_DATA")}):
+            result = interface.route_to_vendor("get_stock_data", "AAPL", "2026-01-01", "2026-01-10")
+        self.assertEqual(result, "AV_DATA")
+
+
+if __name__ == "__main__":
+    unittest.main()