HyperparameterTuner drops content_type when converting InputData to Channel

PySDK Version

PySDK V2 (2.x)
PySDK V3 (3.x)

Describe the bug
When HyperparameterTuner.tune() receives InputData objects as inputs, it converts them to Channel objects internally but drops the content_type field during conversion. This causes built-in algorithms (e.g., XGBoost) to fail with validate_data_file_path errors because the container doesn't know the data format.

To reproduce

from sagemaker.train.configs import InputData
from sagemaker.train.tuner import HyperparameterTuner

train_input = InputData(
    channel_name="train",
    data_source="s3://my-bucket/train/train.csv",
    content_type="csv",  # <-- this gets dropped
)

tuner = HyperparameterTuner(
    model_trainer=model_trainer,
    objective_metric_name="validation:auc",
    hyperparameter_ranges=hyperparameter_ranges,
    objective_type="Maximize",
    max_jobs=12,
    max_parallel_jobs=3,
    strategy="Bayesian",
)

tuner.tune(inputs=[train_input])
# All training jobs fail with:
# AlgorithmError: validate_data_file_path(train_path, content_type)

Root Cause
In sagemaker/train/tuner.py, the _create_hyperparameter_tuning_job method converts InputData → Channel without passing content_type:


# tuner.py lines 1362-1373
```python
if isinstance(inp, InputData):
    input_data_config.append(Channel(
        channel_name=inp.channel_name,
        data_source=DataSource(
            s3_data_source=S3DataSource(
                s3_data_type="S3Prefix",
                s3_uri=inp.data_source,
                s3_data_distribution_type="FullyReplicated"
            )
        )
        # content_type is missing here!
    ))

Suggested Fix

if isinstance(inp, InputData):
    input_data_config.append(Channel(
        channel_name=inp.channel_name,
        content_type=inp.content_type,  # <-- add this
        data_source=DataSource(
            s3_data_source=S3DataSource(
                s3_data_type="S3Prefix",
                s3_uri=inp.data_source,
                s3_data_distribution_type="FullyReplicated"
            )
        )
    ))

Workaround
Pass Channel objects directly instead of InputData:

from sagemaker.core.shapes import Channel, DataSource, S3DataSource

train_input = Channel(
    channel_name="train",
    content_type="csv",
    data_source=DataSource(
        s3_data_source=S3DataSource(
            s3_data_type="S3Prefix",
            s3_uri="s3://my-bucket/train/train.csv",
            s3_data_distribution_type="FullyReplicated",
        )
    ),
)

tuner.tune(inputs=[train_input])  # works correctly

Environment
SageMaker Python SDK version: 3.0.1
Python version: 3.12
Built-in algorithm: XGBoost 1.7-1