[l1l1lkk]

Purpose

to_sampling_params() directly reused the mutable vllm_xargs
dictionary as SamplingParams.extra_args. Merging
kv_transfer_params and ec_transfer_params therefore mutated the
original request object and allowed conversion-specific state to persist
across repeated calls.

This PR copies vllm_xargs before merging transfer metadata for
ChatCompletionRequest, CompletionRequest, and ResponsesRequest.
It preserves the existing merge behavior and empty-value semantics while
separating the request and sampling parameter dictionaries.

A parameterized regression test covers all three request types, including:

• preservation of the original vllm_xargs
• KV and EC transfer parameter merging
• independent dictionary ownership
• repeated conversion without state accumulation
• request serialization and validation round trips

No documentation changes are required because this is an internal
correctness fix with no API changes.

Test Plan

python -m pytest -q tests/entrypoints/openai/test_request_extra_args.py
python -m pytest -q \
  tests/entrypoints/openai/responses/test_sampling_params.py \
  tests/entrypoints/openai/test_stop_token_ids.py
python -m pytest -q tests/test_sampling_params.py
pre-commit run --files \
  vllm/entrypoints/openai/chat_completion/protocol.py \
  vllm/entrypoints/openai/completion/protocol.py \
  vllm/entrypoints/openai/responses/protocol.py \
  tests/entrypoints/openai/test_request_extra_args.py
git diff --check origin/main...HEAD

Test Result
New regression tests: 3 passed
Related OpenAI protocol tests: 16 passed
Sampling parameter tests: 11 passed
Total: 30 passed
Applicable pre-commit checks passed
git diff --check passed

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

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[l1l1lkk]

Hi maintainers, the pre-run-check is blocked by the new-contributor label gate. Could you please add the label? Thanks!

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @l1l1lkk.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork