Fix MLflow autologged model reload fitted-state detection for scikit-learn>=1.8.0 (#1573)

* Initial plan

* Fix MLflow pipeline fitted-state detection

* Strengthen MLflow fitted-state regression test

* Simplify MLflow regression test isolation

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Li Jiang <bnujli@gmail.com>

Author: Copilot

flaml/automl/model.py

@@ -155,6 +155,9 @@ def get_params(self, deep=False):
             params["_estimator_type"] = self._estimator_type
         return params
 
+    def __sklearn_is_fitted__(self):
+        return self._model is not None
+
     def __sklearn_tags__(self):
         """Override sklearn tags to respect the _estimator_type attribute.
 

test/automl/test_mlflow.py

@@ -2,13 +2,35 @@
 
 import mlflow
 import mlflow.entities
+import numpy as np
 import pytest
 from pandas import DataFrame
 from sklearn.datasets import load_iris
+from sklearn.model_selection import train_test_split
+from sklearn.utils.validation import check_is_fitted
 
 from flaml import AutoML
 
 
+def test_autologged_model_round_trip():
+    X, y = load_iris(return_X_y=True, as_frame=True)
+    X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)
+    automl = AutoML()
+    with mlflow.start_run() as run:
+        automl.fit(
+            X_train,
+            y_train,
+            task="classification",
+            estimator_list=["rf"],
+            max_iter=1,
+            verbose=0,
+        )
+
+    loaded = mlflow.sklearn.load_model(f"runs:/{run.info.run_id}/model")
+    check_is_fitted(loaded)
+    assert np.array_equal(automl.predict(X_test), loaded.predict(X_test))
+
+
 class TestMLFlowLoggingParam:
     def test_update_and_install_requirements(self):
         import mlflow