Use probe sequence bottlenecks in harness

src/aituner/harness.py

@@ -249,7 +249,10 @@ def _recent_trial_diagnostics(state: StudyState) -> list[dict[str, Any]]:
                     "best_feasible_probe": _compact_probe(best_probe),
                     "last_probe": _compact_probe(last_probe),
                 }
-                item["active_bottleneck"] = _active_bottleneck(best_probe or last_probe)
+                item["active_bottleneck"] = _active_bottleneck_from_probe_sequence(
+                    probes,
+                    fallback=best_probe or last_probe,
+                )
             elif result.get("all_infeasible_diagnostics"):
                 diag = result["all_infeasible_diagnostics"]
                 item["probe_summary"] = {"all_infeasible": diag}
@@ -345,6 +348,20 @@ def _active_bottleneck(probe: dict[str, Any] | None) -> str:
     return "admission_or_queueing"
 
 
+def _active_bottleneck_from_probe_sequence(
+    probes: list[Any],
+    *,
+    fallback: dict[str, Any] | None,
+) -> str:
+    for probe in reversed(probes):
+        if not isinstance(probe, dict):
+            continue
+        bottleneck = _active_bottleneck(probe)
+        if bottleneck not in {"unknown", "none_obvious"}:
+            return bottleneck
+    return _active_bottleneck(fallback)
+
+
 def _failure_bottleneck(trial: TrialSummary) -> str:
     if trial.failure_stage == "engine_launch":
         return "launch_or_memory"