fix: respect test_index when creating optimization_features row

The get_or_create defaults passed test lists without positional
indexing, so when a higher test_index created the row first its
content landed at index 0 and was overwritten by the lower index
update, losing a test.

django/aiservice/core/log_features/log_features.py

@@ -17,6 +17,15 @@ if TYPE_CHECKING:
 features_api = NinjaAPI(urls_namespace="log_features")
 
 
+def _positional_list(items: list[str] | None, index: int | None) -> list[str | None] | None:
+    """Place a single item at the correct index, padding with None."""
+    if not items or index is None or len(items) != 1:
+        return items
+    result: list[str | None] = [None] * (index + 1)
+    result[index] = items[0]
+    return result
+
+
 @sync_to_async
 @transaction.atomic
 def log_features(
@@ -89,9 +98,9 @@ def log_features(
             "optimized_runtime": optimized_runtime,
             "optimized_line_profiler_results": optimized_line_profiler_results,
             "is_correct": is_correct,
-            "generated_test": generated_tests,
-            "instrumented_generated_test": instrumented_generated_tests,
-            "instrumented_perf_test": instrumented_perf_tests,
+            "generated_test": _positional_list(generated_tests, test_index),
+            "instrumented_generated_test": _positional_list(instrumented_generated_tests, test_index),
+            "instrumented_perf_test": _positional_list(instrumented_perf_tests, test_index),
             "test_framework": test_framework,
             "created_at": datetime,
             "aiservice_commit_id": aiservice_commit,