[reidliu41]

Overview

Create and connect Rust frontend ZMQ sockets on the dedicated runtime so
socket readiness and background transport tasks use the same Tokio I/O
driver. Caller-runtime load or shutdown can no longer delay or terminate
engine communication.

Claims

• Registers HandshakeOwner and Bootstrapped transport I/O with the dedicated
  ZMQ runtime instead of the runtime that calls EngineCoreClient::connect.
• Keeps engine communication functional after the connecting runtime is shut
  down.
• Preserves the existing transport protocol, configuration, and public API.
• Retains cancellation safety while connection setup runs on the dedicated
  runtime.

Validation

cargo nextest run --locked -p vllm-engine-core-client \
  client_transport_outlives_connecting_runtime

A Linux epoll probe with a mock engine confirmed the runtime ownership change:

Measurement	Before	After
ZMQ TCP descriptors on the connecting runtime	4	0
ZMQ TCP descriptors on the dedicated runtime	0	4
Output delay while the connecting runtime was blocked	~4.70 s	0.43–0.75 ms

Details

Tokio associates TCP resources with the I/O driver of the runtime active when
those resources are created. Transport setup previously ran on the caller
runtime, while build_zmq_runtime() was called only after the sockets had
already been bound or connected. Background transport tasks ran on the
dedicated runtime, but socket readiness was still driven by the caller
runtime.

The dedicated runtime is now created before transport setup. The complete
connection path runs on that runtime, and the same runtime is passed into
from_connected for background task execution and lifetime ownership.

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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]

Thanks! This is a good catch!

[BugenZhao]

/ci run

[github-actions]

✅ Triggered Buildkite CI #99162 for commit d7ae0947010b.

ℹ️ This PR is 312 commits behind upstream main. Merged upstream main into this branch as d7ae0947010b before starting CI. Pull the branch before pushing more changes.

[reidliu41]

Thank you for the merge.