[BugenZhao]

Overview

Python vllm serve reads --custom-histogram-buckets, --enable-tower-connector-lora, and --enable-elastic-ep in the frontend, but the Rust frontend did not declare them and dropped them without a warning. This PR makes them fail startup (Unsupported). It also accepts --disable-fastapi-docs as a no-op, since Rust serves no API docs routes.

Claims

• --custom-histogram-buckets, --enable-tower-connector-lora, and --enable-elastic-ep now fail startup on both vllm-rs serve and the Python-supervised --args-json path, instead of being silently ignored by the frontend.
• --disable-fastapi-docs is accepted with a no-op warning instead of failing startup. The Rust frontend serves no OpenAPI, Swagger, or ReDoc endpoints, so it already behaves as if the flag were set.

Validation

Rust CI commands (.buildkite/scripts/run-rust-frontend-cargo-ci.sh, style-clippy and test modes), run from the repository root at the branch tip:

cargo fmt --manifest-path rust/Cargo.toml --all -- --check   # ok
cargo sort --workspace --check rust                          # ok
cargo deny --manifest-path rust/Cargo.toml --config rust/deny.toml check bans   # ok
cargo clippy --manifest-path rust/Cargo.toml --workspace --all-targets --all-features --locked -- -D warnings   # ok
cargo nextest run --manifest-path rust/Cargo.toml --workspace --all-features --locked --no-fail-fast
# 2142 tests run: 2142 passed, 13 skipped

These ran before the structured-outputs commit was reverted; after the revert, cargo nextest run -p vllm-cmd (82 passed) and cargo clippy -p vllm-cmd --all-targets are clean.

Each commit also passes workspace clippy with -D warnings on its own.

New tests in rust/src/cmd/src/cli/tests.rs:

• unsupported_args_fail_startup: each of the three flags fails vllm-rs serve parsing and is listed in the --args-json startup error.
• noop_args_are_accepted: --disable-fastapi-docs parses on both paths.

With rust/src/cmd/src/cli/unsupported.rs reverted to main, both new tests fail.

Details

Where the code lives. Argument recognition belongs to the CLI layer. The flags reuse the existing Unsupported / Noop markers in rust/src/cmd/src/cli/unsupported.rs, which already apply to both the vllm-rs serve (clap) and --args-json (serde) paths. No new mechanism is added.

Why each flag is rejected rather than ignored.

• --custom-histogram-buckets replaces the default buckets of the frontend Prometheus histograms (vllm/v1/metrics/loggers.py). The Rust histograms use fixed buckets, so the requested buckets were silently not applied.
• With --enable-tower-connector-lora, Python's InputProcessor prefixes the multimodal hash with the LoRA name so encoder-cache entries do not collide across adapters (vllm/v1/engine/input_processor.py). Rust always sends the bare hash, so with the flag on, the engine could reuse encoder outputs computed under a different adapter.
• With --enable-elastic-ep, Python's core client hands engine input sockets over during scaling (vllm/v1/engine/core_client.py) and the API server exposes the scaling routes. The Rust frontend has neither, so it could not follow a scale event that the engine went through.

--structured-outputs-config. An earlier revision forwarded it to the managed engine. #62456 parses it in the Rust frontend (it selects the structured-outputs backend) and forwards it itself, so this PR reverts that part and leaves the flag untouched.

Behavior changes for existing users.

• --disable-fastapi-docs now starts instead of failing.
• The three new Unsupported flags were either not honored by the Rust frontend before or could produce wrong results with it.

Not a duplicate. Searching open PRs for each flag finds no PR that changes how the Rust frontend handles them. #50698 (inactive since 2026-10-02) adds a supervisor-side control channel for elastic EP scaling but does not touch --enable-elastic-ep handling in the Rust CLI. #50101 edits the neighboring stream_interval entry in unsupported.rs, a different flag.

AI assistance (Claude Code) was used to prepare this PR. The human submitter reviewed every changed line.

🤖 Generated with Claude Code

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Pull Request Checklist

• I used vLLM's /pr-checklist skill. (Mandatory for agents, optional for humans).

• AI assistance was used during the creation of this PR.

• Design Fit: Minimizes impact on core components, reuses existing functionality, and justifies added complexity.

• Testing and Validation: Validates the change and ensures any added tests are meaningful and reliable, with CI coverage or documented CI resource constraints and validation performed outside CI.

• Code Quality and Style: Keeps code and comments clear and concise, and updates relevant documentation and examples.

• Pull Request Contents: Includes a brief summary and relevant links, supports claims with evidence, explains root causes and implementation trade-offs, and follows the contributing guide.

[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.

[BugenZhao]

/ci run

[github-actions]

✅ Triggered Buildkite CI #96154 for commit f961ed6be6a7.

ℹ️ This PR is 83 commits behind upstream main. Merged upstream main into this branch as f961ed6be6a7 before starting CI. Pull the branch before pushing more changes.