ModelBuilder fails w/ DJL container using HF_MODEL_ID

Start at ModelBuilder._build_for_passthrough() and trace the values passed into _create_model(). Reproduce the passthrough build with image_uri and HF_MODEL_ID, then verify that a successful CreateModel request omits ModelDataUrl and the container can load the configured model from S3.

PySDK Version

• PySDK V2 (2.x)
• PySDK V3 (3.4.0)

Describe the bug
When using ModelBuilder in "passthrough" mode (image_uri + env_vars, no model
or inference_spec), build() fails with a ValidationException because a
non-existent S3 path is injected as ModelDataUrl in the CreateModel request.

Passthrough mode is the intended path for deploying models on custom/DJL
containers where the container itself handles model loading (e.g. via
HF_MODEL_ID env var pointing to S3).

Expected behavior
Expected: Model created with no ModelDataUrl (container loads via HF_MODEL_ID)
Actual: ValidationException -- "Could not find model data at
s3:///model-builder///"

Suggested Fix

In _build_for_passthrough(), also clear s3_model_data_url:

def _build_for_passthrough(self) -> Model:
    if not self.image_uri:
        raise ValueError("image_uri is required for pass-through cases")
    self.s3_upload_path = None
    self.s3_model_data_url = None   # <-- add this line
    return self._create_model()

To reproduce

from sagemaker.core.helper.session_helper import Session, get_execution_role
from sagemaker.serve.model_builder import ModelBuilder

sagemaker_session = Session()
region = sagemaker_session.boto_session.region_name
role = get_execution_role(sagemaker_session, use_default=True)
bucket = sagemaker_session.default_bucket()

image_uri = f"763104351884.dkr.ecr.{region}.amazonaws.com/djl-inference:0.33.0-lmi15.0.0-cu128"

model_builder = ModelBuilder(
    image_uri=image_uri,
    role_arn=role,
    sagemaker_session=sagemaker_session,
    instance_type="ml.g5.2xlarge",
    env_vars={
        "HF_MODEL_ID": f"s3://{bucket}/models/any-model",
        "OPTION_ROLLING_BATCH": "vllm",
    },
)

model_builder.build(model_name="passthrough-bug-repro")