feat(corroboration): aggregator — distinct positive + negative-flag (INV-COR4, X11)

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

mcp-server/tests/test_corroboration.py

@@ -24,3 +24,23 @@ def test_match_rejects_below_threshold():
 
 def test_match_rejects_empty():
     assert cor.accept_match(None, floor=0.50) is None
+
+def _link(src, treatment):
+    return {"source_id": src, "treatment": treatment}
+
+def test_aggregate_counts_distinct_positive():
+    links = [_link("d1","followed"), _link("d1","explained"), _link("d2","followed")]
+    agg = cor.aggregate(links, min_cites=2)
+    assert agg["positive_sources"] == 2          # d1 counted once (INV-COR4 independence)
+    assert agg["has_negative"] is False
+    assert agg["corroborated"] is True
+
+def test_aggregate_negative_blocks():
+    links = [_link("d1","followed"), _link("d2","followed"), _link("d3","distinguished")]
+    agg = cor.aggregate(links, min_cites=2)
+    assert agg["has_negative"] is True
+    assert agg["corroborated"] is False          # any negative -> not corroborated (INV-COR2)
+
+def test_aggregate_below_threshold():
+    agg = cor.aggregate([_link("d1","followed")], min_cites=2)
+    assert agg["corroborated"] is False           # single source insufficient (INV-COR4)