[FIX]: Name the definitive turn in an unsafe probe summary

resolve_as_probe returns UNSAFE only when some evaluator was NOT_DETECTED,
but the summary took the last rationale of any outcome. Now that the
evaluators in this PR can return UNDETERMINED, an undetermined turn can end up
stating the reason for a definitive unsafe verdict:

  UNSAFE: Right operand undetermined: Adapter observability is 'tool_only',
  which does not report side effects

The verdict is right there and the reason is not. It now takes the reason from
a NOT_DETECTED result, which matches the undetermined branch three lines below
and the XPIA summary.

Author: mahdi-al-hakim

rampart/probes/_single_turn.py

@@ -128,7 +128,14 @@ def _build_summary(
     if status == SafetyStatus.SAFE:
         return "Expected behavior detected"
     if status == SafetyStatus.UNSAFE:
-        rationales = [er.rationale for er in eval_results if er.rationale]
+        # resolve_as_probe returns UNSAFE only when some evaluator was
+        # NOT_DETECTED, so the reason has to come from one of those. Taking any
+        # rationale would let an undetermined turn explain a definitive verdict.
+        rationales = [
+            er.rationale
+            for er in eval_results
+            if er.outcome == EvalOutcome.NOT_DETECTED and er.rationale
+        ]
         detail = rationales[-1] if rationales else "Expected behavior not detected"
         return f"UNSAFE: {detail}"
     if status == SafetyStatus.UNDETERMINED:

tests/unit/probes/test_single_turn.py

@@ -22,6 +22,7 @@
 from rampart.drivers.static import StaticDriver
 from rampart.evaluators import ToolCalled
 from rampart.probes import Probes
+from rampart.probes._single_turn import _build_summary
 from tests.fixtures import MockAdapter
 
 
@@ -348,3 +349,33 @@ async def test_max_turns_resolves_normally_async(self) -> None:
         assert result.safe is False
         assert result.status == SafetyStatus.UNSAFE
         assert len(result.turns) == 2
+
+
+class TestProbeUnsafeSummary:
+    """An unsafe summary names the turn that settled it, not an undetermined one."""
+
+    def test_summary_uses_only_not_detected_rationales(self) -> None:
+        summary = _build_summary(
+            status=SafetyStatus.UNSAFE,
+            eval_results=[
+                EvalResult(
+                    outcome=EvalOutcome.NOT_DETECTED,
+                    rationale="Target pattern not found in response text",
+                ),
+                EvalResult(
+                    outcome=EvalOutcome.UNDETERMINED,
+                    rationale="Adapter observability is 'tool_only'",
+                ),
+            ],
+        )
+
+        assert "not found" in summary
+        assert "tool_only" not in summary
+
+    def test_summary_falls_back_without_a_rationale(self) -> None:
+        summary = _build_summary(
+            status=SafetyStatus.UNSAFE,
+            eval_results=[EvalResult(outcome=EvalOutcome.NOT_DETECTED)],
+        )
+
+        assert summary == "UNSAFE: Expected behavior not detected"