refactor(dataflows): read company identity and settlement prices through the data layer

- the Yahoo vendor owns get_company_profile and get_closes; agent_utils and the graph no longer import yfinance
- a test keeps vendor libraries inside dataflows

tests/test_layering.py

@@ -0,0 +1,35 @@
+"""Only the data layer imports vendor libraries.
+
+Vendor calls belong in dataflows, where failures are raised as VendorError
+subclasses; a call made elsewhere can report an outage as a fact about the market.
+"""
+
+import ast
+from pathlib import Path
+
+import pytest
+
+ROOT = Path(__file__).resolve().parents[1]
+VENDOR_LIBRARIES = {"yfinance"}
+
+
+def _imports(path: Path) -> set[str]:
+    names = set()
+    for node in ast.walk(ast.parse(path.read_text(encoding="utf-8"))):
+        if isinstance(node, ast.Import):
+            names |= {a.name.split(".")[0] for a in node.names}
+        elif isinstance(node, ast.ImportFrom) and node.module and not node.level:
+            names.add(node.module.split(".")[0])
+    return names
+
+
+@pytest.mark.unit
+def test_vendor_libraries_are_imported_only_by_the_data_layer():
+    data_layer = ROOT / "tradingagents" / "dataflows"
+    offenders = sorted(
+        str(path.relative_to(ROOT))
+        for package in ("tradingagents", "cli")
+        for path in (ROOT / package).rglob("*.py")
+        if data_layer not in path.parents and _imports(path) & VENDOR_LIBRARIES
+    )
+    assert offenders == []