feat(corroboration): treatment classifier + polarity (INV-COR2, X11)

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

mcp-server/tests/test_corroboration.py

@@ -0,0 +1,17 @@
+from __future__ import annotations
+import pytest
+from legal_mcp.services import corroboration as cor
+
+@pytest.mark.parametrize("raw,expected", [
+    ({"treatment": "followed"}, "followed"),
+    ({"treatment": "OVERRULED"}, "overruled"),     # case-insensitive
+    ({"treatment": "bananas"}, "mentioned"),         # unknown -> neutral default
+    ({}, "mentioned"),                               # missing -> neutral default
+])
+def test_coerce_treatment(raw, expected):
+    assert cor._coerce_treatment(raw) == expected
+
+def test_treatment_polarity():
+    assert cor.is_positive("followed") and cor.is_positive("explained")
+    assert cor.is_negative("distinguished") and cor.is_negative("overruled")
+    assert not cor.is_positive("mentioned") and not cor.is_negative("mentioned")