[V1][Bugfix] Fix V1 TP trust-remote-code (#11182)

Signed-off-by: Tyler Michael Smith <tyler@neuralmagic.com>

vllm/v1/engine/core.py

@@ -14,6 +14,8 @@
 from vllm.config import CacheConfig, VllmConfig
 from vllm.executor.multiproc_worker_utils import get_mp_context
 from vllm.logger import init_logger
+from vllm.transformers_utils.config import (
+    maybe_register_config_serialize_by_value)
 from vllm.usage.usage_lib import UsageContext
 from vllm.v1.core.scheduler import Scheduler
 from vllm.v1.engine import (EngineCoreOutput, EngineCoreOutputs,
@@ -241,6 +243,9 @@ def run_engine_core(*args, **kwargs):
         # processes to terminate without error
         shutdown_requested = False
 
+        # Ensure we can serialize transformer config after spawning
+        maybe_register_config_serialize_by_value()
+
         def signal_handler(signum, frame):
             nonlocal shutdown_requested
             if not shutdown_requested: