refactor(data): unify vendor errors under a VendorError hierarchy

Every condition where a vendor cannot return usable data now derives from a
single VendorError base (errors.py): NoMarketDataError, VendorRateLimitError,
and VendorNotConfiguredError (still a ValueError for back-compat). Vendor-named
errors subclass the generic bases, and the router catches the base types, so a
new vendor needs no new except clause. Not-configured now has explicit
try-next-vendor handling instead of falling through the generic catch-all. The
number of error types tracks the number of distinct router reactions, not the
number of causes.

tests/test_vendor_errors.py

@@ -0,0 +1,105 @@
+"""The vendor data-error hierarchy: every "vendor couldn't return usable data"
+condition derives from VendorError, so the router catches base types and any
+vendor slots in without new handling.
+"""
+import copy
+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.alpha_vantage_common import (
+    AlphaVantageNotConfiguredError,
+    AlphaVantageRateLimitError,
+)
+from tradingagents.dataflows.config import set_config
+from tradingagents.dataflows.errors import (
+    NoMarketDataError,
+    VendorError,
+    VendorNotConfiguredError,
+    VendorRateLimitError,
+)
+from tradingagents.dataflows.fred import FredNotConfiguredError
+
+
+@pytest.mark.unit
+class HierarchyTests(unittest.TestCase):
+    def test_all_conditions_derive_from_vendor_error(self):
+        for cls in (NoMarketDataError, VendorRateLimitError, VendorNotConfiguredError):
+            self.assertTrue(issubclass(cls, VendorError))
+
+    def test_not_configured_is_still_a_value_error(self):
+        # Back-compat: existing `except ValueError` callers keep working.
+        self.assertTrue(issubclass(VendorNotConfiguredError, ValueError))
+
+    def test_vendor_named_errors_subclass_the_generic_bases(self):
+        self.assertTrue(issubclass(AlphaVantageRateLimitError, VendorRateLimitError))
+        self.assertTrue(issubclass(AlphaVantageNotConfiguredError, VendorNotConfiguredError))
+        self.assertTrue(issubclass(FredNotConfiguredError, VendorNotConfiguredError))
+        # ... and therefore still ValueErrors
+        self.assertTrue(issubclass(FredNotConfiguredError, ValueError))
+
+    def test_symbol_utils_reexports_no_market_data_error(self):
+        from tradingagents.dataflows.symbol_utils import (
+            NoMarketDataError as ReExported,
+        )
+        self.assertIs(ReExported, NoMarketDataError)
+
+
+@pytest.mark.unit
+class RouterHandlesBaseTypesTests(unittest.TestCase):
+    def setUp(self):
+        config_module._config = copy.deepcopy(default_config.DEFAULT_CONFIG)
+
+    def tearDown(self):
+        config_module._config = copy.deepcopy(default_config.DEFAULT_CONFIG)
+
+    def test_rate_limit_subclass_caught_by_base(self):
+        # A vendor-named rate-limit error skips to the next vendor in the chain.
+        set_config({"data_vendors": {"core_stock_apis": "alpha_vantage,yfinance"}})
+
+        def _throttled(*a, **k):
+            raise AlphaVantageRateLimitError("slow down")
+
+        with mock.patch.dict(
+            interface.VENDOR_METHODS,
+            {"get_stock_data": {"alpha_vantage": _throttled, "yfinance": lambda *a, **k: "YF"}},
+            clear=False,
+        ):
+            out = interface.route_to_vendor("get_stock_data", "AAPL", "2026-01-01", "2026-01-10")
+        self.assertEqual(out, "YF")
+
+    def test_not_configured_falls_through_to_next_vendor(self):
+        set_config({"data_vendors": {"core_stock_apis": "alpha_vantage,yfinance"}})
+
+        def _unconfigured(*a, **k):
+            raise AlphaVantageNotConfiguredError("no key")
+
+        with mock.patch.dict(
+            interface.VENDOR_METHODS,
+            {"get_stock_data": {"alpha_vantage": _unconfigured, "yfinance": lambda *a, **k: "YF"}},
+            clear=False,
+        ):
+            out = interface.route_to_vendor("get_stock_data", "AAPL", "2026-01-01", "2026-01-10")
+        self.assertEqual(out, "YF")
+
+    def test_sole_unconfigured_vendor_surfaces_the_error(self):
+        # With no fallback, the not-configured condition must surface (not vanish).
+        set_config({"data_vendors": {"core_stock_apis": "alpha_vantage"}})
+
+        def _unconfigured(*a, **k):
+            raise AlphaVantageNotConfiguredError("no key")
+
+        with mock.patch.dict(
+            interface.VENDOR_METHODS,
+            {"get_stock_data": {"alpha_vantage": _unconfigured}},
+            clear=False,
+        ), self.assertRaises(AlphaVantageNotConfiguredError):
+            interface.route_to_vendor("get_stock_data", "AAPL", "2026-01-01", "2026-01-10")
+
+
+if __name__ == "__main__":
+    unittest.main()