[BugFix] Remove stage_configs_path validation

[amy-why-3459]

PLEASE FILL IN THE PR DESCRIPTION HERE ENSURING ALL CHECKLIST ITEMS (AT THE BOTTOM) HAVE BEEN CONSIDERED.

Purpose

Remove the stage_configs_path check to avoid throwing a runtime error during L4 test cases.

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/vllm-omni/vllm_omni/entrypoints/cli/main.py", line 63, in <module>
    main()
  File "/vllm-omni/vllm_omni/entrypoints/cli/main.py", line 57, in main
    args.dispatch_function(args)
  File "/vllm-omni/vllm_omni/entrypoints/cli/serve.py", line 94, in cmd
    run_headless(args)
  File "/vllm-omni/vllm_omni/entrypoints/cli/serve.py", line 552, in run_headless
    vllm_config, executor_class = build_vllm_config(
                                  ^^^^^^^^^^^^^^^^^^
  File "/vllm-omni/vllm_omni/engine/stage_init_utils.py", line 326, in build_vllm_config
    vllm_config = omni_engine_args.create_engine_config(
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/vllm/engine/arg_utils.py", line 1549, in create_engine_config
    model_config = self.create_model_config()
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/vllm-omni/vllm_omni/engine/arg_utils.py", line 198, in create_model_config
    raise RuntimeError(
RuntimeError: create_model_config() should not be called when stage_configs_path is set. Per-stage model configs are resolved from the stage config YAML.

Test Plan

pytest -sv test_qwen3_omni_expansion.py -m "advanced_model" --run-level "advanced_model"

Test Result

(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/messages/count_tokens, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /inference/v1/generate, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /scale_elastic_ep, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /is_scaling_elastic_ep, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/chat/completions/render, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/completions/render, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/chat/completions, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/audio/speech, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/audio/speech/batch, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/audio/voices, Methods: GET
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/audio/voices, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/audio/voices/{name}, Methods: DELETE
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /health, Methods: GET
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/models, Methods: GET
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/images/generations, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/images/edits, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/videos, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/videos/sync, Methods: POST
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/videos, Methods: GET
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/videos/{video_id}, Methods: GET
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/videos/{video_id}, Methods: DELETE
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:46] Route: /v1/videos/{video_id}/content, Methods: GET
(APIServer pid=3242233) INFO 04-13 14:51:47 [launcher.py:57] Route: /v1/audio/speech/stream, Endpoint: streaming_speech
OmniServerStageCli ready on 127.0.0.1:35405
OmniServer started successfully

---

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan. Please provide the test scripts & test commands. Please state the reasons if your codes don't require additional test scripts. For test file guidelines, please check the test style doc
• The test results. Please paste the results comparison before and after, or the e2e results.
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model. Please run mkdocs serve to sync the documentation editions to ./docs.
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[amy-why-3459]

@lishunyang12 @princepride @hsliuustc0106 @wuhang2014 PTAL

[hsliuustc0106]

PR #2741 - [BugFix] Remove stage_configs_path validation

OVERALL: NO BLOCKERS
VERDICT: COMMENT

Correctness: PASS
Reliability: PASS
Breaking: PASS
Tests: PASS (e2e test shows successful start)
Documentation: PASS (inline doc added)
Security: PASS

Summary: Remove stage_configs_path validation to fix L4 tests (RuntimeError: 'model_config'). 0 add, 5 del. Test result shows successful start after fix. No blockers.

[Gaohan123]

LGTM

[timzsu]

LGTM. The test I added is overly aggressive.

[amy-why-3459]

@hsliuustc0106 @Gaohan123 I think this PR is ready and can be merged. The docs haven't passed testing due to insufficient resources.