[BUG] Cowork: Code block copy button not working in a new window (macOS)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

The copy button (clipboard icon) on code blocks does not work when the chat is opened in a NEW / separate window (multi-window).

• Clicking the copy button has no effect: nothing is copied, no "Copied!" feedback appears.
• Clipboard contents stay unchanged (Cmd+V pastes nothing / the previous content).
• The button looks clickable but produces no action.

This is essentially the same problem as the previously closed issue #18286, with the key difference that it reproduces specifically in a new (separate) window rather than the main window.

Workaround: manual drag-select + Cmd+C still works.

What Should Happen?

Clicking the copy button should copy the code block contents to the clipboard and show visual feedback (e.g. a "Copied!" tooltip), the same as in the main window.

Error Messages/Logs

Steps to Reproduce

1. Open a Claude Code / Cowork session in a NEW window (multi-window).
2. Ask Claude to generate any code block (e.g. bash commands or Python).
3. Click the copy button (clipboard icon) in the top-right corner of the code block.
4. Try to paste (Cmd+V) anywhere -> nothing is pasted.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude 1.11187.4 (584005) 2026-06-05T20:15:04.000Z

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Same behavior as the closed issue #18286 (Cowork: Code block copy button not working). The only difference here is that it occurs in a new / separate window. OS: macOS 15.7.3 (24G419).