[Bug]: Cursor Steer waits for the turn to finish #14585

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

1. Set Follow-up behavior to Steer and pick a Cursor model.
2. Send: Use your shell tool to run sleep 45. Then reply with exactly DONE.
3. While sleep 45 runs, send: Stop and reply with exactly STEERED_NOW.

Expected behavior

Cursor gets the steer right away and answers STEERED_NOW, as it does for Grok.

Actual behavior

Steer acts like Queue. Cursor finishes sleep 45, answers DONE, and only then answers STEERED_NOW, about 50s after the steer was sent.

The ACP runtime runs one session/prompt at a time (#3156), and the Cursor adapter sends the steer as a second prompt without cancelling the first, so it waits behind it. Cursor steering (#3041) predates that change.

I use Cursor in T3 Code as a daily driver, and this breaks steering in everyday use. I know outside PRs are expected to stay small and start from a triaged issue. The fix here is scoped to this one behavior, but it touches the Cursor adapter plus a small contracts and web change for Queue, so I'm opening the PR alongside this issue rather than waiting.

Impact

Major degradation or frequent failure

Version or commit

main @ 5cc99e1

Environment

Cursor CLI 2026.09.28-64d2043 on macOS 27, Ubuntu (Node 24), and Windows 11

Workaround

Press Stop, then send the message again.