Fix: Resolve circular import in model_loader/utils.py

[nandan2003]

Purpose

Fixes a circular import error where vllm.model_executor.model_loader.utils could not be imported because it attempted to import from models.adapters at the top level, while models.adapters (indirectly) depends on utils.

Fixes #29110

Test Plan

I verified this locally by attempting to import the module in an isolated script to ensure the circular dependency chain is broken.

Verification Script:

import torch

# Mock compile to bypass python 3.14+ restriction if needed for testing import logic only
def no_op_compile(*args, **kwargs):
    def decorator(func):
        return func
    return decorator
torch.compile = no_op_compile

try:
    from vllm.model_executor.model_loader.utils import process_weights_after_loading
    print("Success! Circular dependency is fixed.")
except ImportError as e:
    print(f"FAILURE: {e}")

Test Result

• Before Fix: ImportError: cannot import name 'process_weights_after_loading' from 'vllm.model_executor.model_loader.utils'
• After Fix: Success! Circular dependency is fixed.

Additional Context

The import of as_embedding_model, as_reward_model, as_seq_cls_model, and try_create_mm_pooling_model_cls was moved from the global scope of utils.py into get_model_architecture() where they are actually used. This defers the import execution and resolves the cycle.

[gemini-code-assist]

Code Review

This pull request correctly resolves a circular import issue by moving imports from the global scope into the function where they are used. This is a good and standard approach. However, I've found a critical issue where the type hint for the _get_model_architecture function was changed, making it inconsistent with its implementation and usage, which will likely lead to errors. Please see the detailed comment for the required fix.

[nandan2003]

Hi

The pre-commit/mypy failures in vllm/v1/worker/... appear unrelated to my changes.

My modification is strictly isolated to vllm/model_executor/model_loader/utils.py to resolve the circular dependency. Verified the fix locally by successfully importing the module.