[Config Refactor] sentinel default precedence (#3078)

Signed-off-by: lishunyang <lishunyang12@163.com>
Signed-off-by: xiaohajiayou <923390377@qq.com>
Co-authored-by: lishunyang <lishunyang12@163.com>

vllm_omni/entrypoints/cli/serve.py

@@ -9,7 +9,6 @@ import argparse
 import json
 import os
 import signal
-import sys
 from types import FrameType
 from typing import Any
 
@@ -20,9 +19,9 @@ from vllm.entrypoints.utils import VLLM_SUBCMD_PARSER_EPILOG
 from vllm.logger import init_logger
 from vllm.utils.argparse_utils import FlexibleArgumentParser
 
+from vllm_omni.engine.arg_utils import nullify_stage_engine_defaults
 from vllm_omni.entrypoints.cli.logo import log_logo
 from vllm_omni.entrypoints.openai.api_server import omni_run_server
-from vllm_omni.entrypoints.utils import detect_explicit_cli_keys
 
 logger = init_logger(__name__)
 
@@ -95,10 +94,6 @@ class OmniServeCommand(CLISubcommand):
         if hasattr(args, "model_tag") and args.model_tag is not None:
             args.model = args.model_tag
 
-        # Stash the set of long-option keys the user actually typed so the
-        # stage-config factory can give YAML precedence over argparse defaults.
-        args._cli_explicit_keys = detect_explicit_cli_keys(sys.argv[1:], OmniServeCommand._parser)
-
         if args.headless:
             run_headless(args)
         else:
@@ -485,6 +480,8 @@ class OmniServeCommand(CLISubcommand):
         # Stash via type(self) so the docs hook (which execs this function in a
         # sandboxed globals dict via ``DummySelf``) doesn't fail on a NameError.
         type(self)._parser = serve_parser
+
+        nullify_stage_engine_defaults(serve_parser)
         return serve_parser
 
 
@@ -540,15 +537,11 @@ def run_headless(args: argparse.Namespace) -> None:
         raise ValueError("headless mode requires worker_backend=multi_process")
 
     args_dict = vars(args).copy()
-    # Preserve the explicit-keys set captured at parse time so per-stage yaml
-    # values (e.g. stage 1's ``gpu_memory_utilization: 0.5``) are not
-    # overwritten by argparse defaults for flags the user didn't type.
-    cli_explicit_keys = args_dict.pop("_cli_explicit_keys", None)
+    args_dict.pop("_cli_explicit_keys", None)
     config_path, stage_configs = load_and_resolve_stage_configs(
         model,
         args_dict.get("stage_configs_path"),
         args_dict,
-        cli_explicit_keys=cli_explicit_keys,
     )
 
     # Locate the stage config that matches stage_id.