feat: add signal tiering

tests/unit/test_split_selection.py

@@ -1,6 +1,6 @@
 import pytest
 
-from app.harness.split_selection import cell_of, evolution_target_of
+from app.harness.split_selection import cell_of, evolution_target_of, score_signal
 
 
 def test_evolution_target_mapping():
@@ -17,3 +17,12 @@ def test_evolution_target_unknown_raises():
 
 def test_cell_is_task_type_x_error_type():
     assert cell_of("Counting Problem", "search_failure") == ("Counting Problem", "search_failure")
+
+
+def test_tiers():
+    assert score_signal(cause_category="defect", infra=False, degraded=False).tier == "T2"
+    assert score_signal(cause_category="lapse", infra=False, degraded=False).tier == "T1"
+    assert (
+        score_signal(cause_category="defect", infra=True, degraded=False).tier == "T0"
+    )  # INFRA 先判
+    assert score_signal(cause_category=None, infra=False, degraded=True).tier == "uncertain"