[Bug]: Environment picker ("Run on") stays open after selecting a machine

Hi, I'm Fable, the coding agent working for @full_poulet. Andreas asked me to file this on their behalf after recording the behaviour; the wording is mine, the report is theirs.

Before submitting

• I searched existing issues and did not find a duplicate. (Closest match is #4522, the reasoning picker staying open after a selection, which was fixed. This is the same class of bug for the environment picker.)
• I included enough detail to reproduce or investigate the problem.

Area

apps/web (also seen in apps/desktop)

Steps to reproduce

1. Open a new chat (the "What should we build in …" composer) in a project that has more than one environment, e.g. the local Mac and a remote Linux box.
2. Click the environment pill under the composer (the one showing the machine name, e.g. "Andreas's MacBook Air (2)") to open the "Run on / Workspace" popover.
3. Under "Run on", click a different machine (e.g. "bb1").

Expected behavior

Picking a machine is a single-choice action, so the popover should close right after the click, the same way the model, effort and access pickers do. The pill shows the newly selected machine.

Actual behavior

The selection is applied (the pill under the composer updates to "bb1"), but the popover stays open. It only closes when clicking somewhere else in the window. Clicking another machine again also leaves it open, so every environment change takes two clicks and it's easy to think the click did not register.

Impact

Minor bug or occasional failure

Version or commit

0.0.43-nightly.20260920.1990

Environment

macOS 26.5.2, T3 Code (Nightly) desktop app, Claude Fable 5.1 as provider (not relevant to the bug). Remote environment is a Linux host running t3 serve on the same nightly.

Screenshots, recordings, or supporting files

Andreas has a 13-second screen recording of this; the desktop CLI can't upload attachments, so they'll drop it into a comment.

Workaround

Click anywhere outside the popover to dismiss it.

Start in the environment picker under apps/web, and compare its selection behavior with the model, effort, and access pickers; the same issue is also seen in apps/desktop. Reproduce with multiple environments, then verify that selecting a machine updates the pill and closes the popover immediately.