fix: preserve fitted order of future exogenous columns

[Anton Soloviev (antonsoo)]

Select future covariate columns in the stored training order before converting X_df into a grouped array. The existing shape and required-name checks stay in place.

Currently the required features are checked by name but passed to the model in the incoming dataframe order. Reordering two named columns silently exchanges their fitted coefficients:

import numpy as np
import pandas as pd
from sklearn.linear_model import LinearRegression
from statsforecast import StatsForecast
from statsforecast.models import SklearnModel
from statsforecast.utils import AirPassengersDF

df = AirPassengersDF.copy()
df["trend"] = (df.ds.dt.year - 1949) * 12 + df.ds.dt.month
df["season"] = np.sin(2 * np.pi * df.ds.dt.month / 12)
sf = StatsForecast(models=[SklearnModel(LinearRegression())], freq="ME")
sf.fit(df.iloc[:-12])
future = df.iloc[-12:].drop(columns="y")
expected = sf.predict(h=12, X_df=future)
actual = sf.predict(h=12, X_df=future[["unique_id", "ds", "season", "trend"]])
pd.testing.assert_frame_equal(actual, expected)

This fails on current main, with a maximum prediction difference of about 2,654 passengers, and passes with this change.

Validation:

• Twelve before-failing regression cases cover forecast, fit_predict, and fit().predict(), pandas/Polars, and one/two workers.
• Real AirPassengers and monthly CO2 data, with native ARIMA and scikit-learn regression, were checked against separately fitted single-series models. Across 72 dtype/backend/worker/horizon/API configurations, 1,824 incorrect reordered forecast values become zero; the maximum reference difference is 5.69e-14. All 72 correctly ordered controls retain identical result bytes.
• Core and focused tests: 60 passed. Project pre-commit hooks pass.

The real-data checks establish covariate alignment, not improved forecast accuracy. Distributed Spark/Dask/Ray execution was not exercised.

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-12T21:31:42.440991Z	34cf5e8	New commits

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[José Morales (jmoralez)]

Thanks! Can you please sign the CLA? Once that's done this'll be ready to be merged