[BUG] Fullscreen renderer corrupts the SYSTEM-WIDE macOS clipboard (copy/paste breaks in ALL apps), Terminal.app

⚠️ Severity: system-wide, not app-local

The fullscreen renderer doesn't just break copy/paste inside Claude Code — while CC is running in fullscreen, copy/paste stops working across the entire macOS system, in other applications too (browser, editors, Finder, etc.). The system clipboard is effectively broken for as long as CC is in fullscreen mode.

This is why it's so hard to diagnose: the symptom shows up in unrelated apps, so users spend weeks blaming their OS/terminal/hardware before realizing a backgrounded Claude Code fullscreen session is the cause.

What happens

• Cmd+C (copy) and Cmd+V (paste) fail — both directions — and not only in Claude Code but in all applications while CC runs in the fullscreen renderer.
• Switching to the default renderer with /tui default immediately restores normal system-wide copy/paste.
• Switching back to /tui fullscreen breaks it again.

So the fullscreen renderer is the cause, and the blast radius is the whole OS clipboard, not just CC's UI.

Steps to reproduce

1. macOS, Apple Terminal.app.
2. Run Claude Code in the fullscreen renderer (confirm with /tui → "fullscreen"; it's the default — no CLAUDE_CODE_NO_FLICKER env var needed).
3. With CC running, switch to another app (browser, text editor) and try Cmd+C / Cmd+V there.
4. Clipboard copy/paste is broken system-wide.
5. Back in CC, run /tui default → system clipboard works again everywhere. /tui fullscreen → breaks again.

Expected

Claude Code's renderer must not interfere with the OS-native system clipboard for other applications. Cmd+C/Cmd+V should work everywhere (and inside CC), as they do in the default renderer.

Actual

While CC is in fullscreen, the macOS system clipboard is broken in all apps. Only /tui default restores it.

Workaround

/tui default (gives up fullscreen's flicker-free rendering to get the system clipboard back).

Environment

• Claude Code: 2.1.196
• Terminal: Apple_Terminal 470.2 (Terminal.app)
• OS: macOS 26.5.1 (arm64)
• TERM: xterm-256color
• CLAUDE_CODE_NO_FLICKER: unset (fullscreen is the default renderer in this version)

Notes

Existing related issues are WSL-specific (#64642 docs, #50605 closed WSL2 clipboard mojibake). This is macOS Terminal.app, both-directions, system-wide, and not previously reported for this platform. Given the system-wide impact, this seems higher severity than an in-app rendering quirk.