Make strong incumbent trigger validation phase

tests/test_core_flow.py

@@ -411,11 +411,16 @@ class CoreFlowTests(unittest.TestCase):
             guard = context["convergence_guard"]["strong_incumbent"]
             self.assertTrue(guard["guard_active"])
             self.assertGreaterEqual(guard["incumbent_gain_vs_baseline"], 3.0)
-            self.assertTrue(
+            self.assertFalse(
                 context["convergence_guard"][
                     "should_stop_if_no_harness_can_justify_a_new_adjacent_probe"
                 ]
             )
+            self.assertEqual(
+                context["convergence_guard"]["reason"],
+                "strong_incumbent_requires_validation_probes",
+            )
+            self.assertIn("validate", guard["recommended_next_action"])
 
     def test_trace_input_length_filter_keeps_only_matching_rows(self) -> None:
         with tempfile.TemporaryDirectory() as tmp:
@@ -2418,6 +2423,21 @@ class CoreFlowTests(unittest.TestCase):
             ["throughput: higher", "ttft: lower"],
         )
 
+    def test_proposal_observation_accepts_object(self) -> None:
+        proposal = Proposal.from_dict(
+            {
+                "observation": {
+                    "incumbent_trial": "trial-0002",
+                    "boundary_signal": "tpot cliff",
+                },
+                "diagnosis": "validate incumbent",
+                "config_patch": {"env_patch": {}, "flag_patch": {"max-num-seqs": 160}},
+                "expected_effects": ["more TPOT headroom"],
+            }
+        )
+        self.assertIn('"incumbent_trial": "trial-0002"', proposal.observation)
+        self.assertEqual(proposal.diagnosis, "validate incumbent")
+
     def test_proposal_accepts_should_stop(self) -> None:
         proposal = Proposal.from_dict(
             {