Build LMCache#2653's diagnostic dump proved the transformers install is
correct and that isolated `from transformers import GenerationConfig`
works fine inside the failing pod. The failure only manifests through
vllm's CLI entry point.

Root cause is in vllm/entrypoints/cli/main.py itself: the module spawns
a daemon thread (`_bg_preload_torch`) that calls `import torch` and
then `import transformers` at module-scope, racing the main thread
which proceeds into main() -> vllm.entrypoints.cli.benchmark.main ->
... -> vllm.transformers_utils.config:18 ->
`from transformers import GenerationConfig, PretrainedConfig`.

On the K3s pods the race lands deterministically in a state where
transformers' _LazyModule._class_to_module cannot resolve
'GenerationConfig' (even though, as the diagnostic confirms, the
fully-initialized module contains it). A fresh local venv with
identical versions cannot reproduce it, consistent with a
timing-sensitive race. The diagnostic ran `import transformers` on
the main thread as its first action, which is exactly why it didn't
trip the race.

Fix: after `uv pip install -U vllm ...`, patch
vllm/entrypoints/cli/main.py to add `import transformers` at module
top, before the BG thread is spawned. Once transformers is already
in sys.modules with _LazyModule fully initialized, the BG thread's
`import transformers` becomes a no-op and the later
`from transformers import ...` on the main thread is just an
attribute lookup against a fully-ready module.

The patch is idempotent (marker comment prevents double-application)
and fails loudly if vllm restructures the file. Once upstream vllm
fixes this on their side, this patch block can be removed.

Signed-off-by: Samuel Shen <slshen@tensormesh.ai>