Fullscreen TUI mode breaks terminal text copy in browser-based terminals (code-server/xterm.js) due to mouse-tracking capture

Environment

• Claude Code version: 2.1.199
• Terminal: code-server (VS Code web) integrated terminal, built on xterm.js
• Access: browser, plain HTTP (not a factor in root cause, ruled out separately)
• ~/.claude/settings.json: "tui": "fullscreen" (enabled via the recent upgrade prompt)

Bug

When "tui": "fullscreen" is enabled, selecting text with the mouse in
Claude Code's terminal output no longer performs native browser/terminal
text selection. Instead, a status hint appears:

send N chars via OSC 52. if paste fails, hold shift while selecting for native copy

Both Ctrl+C and right-click "Copy" fail to copy anything to the
clipboard, with no console errors. The suggested workaround (hold Shift
while selecting, or Shift while right-clicking) does not work in this
environment.

Root cause (as far as we could tell)

Fullscreen mode requests terminal mouse-tracking/mouse-reporting, so
mouse drag events are forwarded to Claude Code's renderer instead of
triggering native OS/browser text selection — the same mechanism used
by vim/htop/tmux-with-mouse-on. Claude Code then relies on an OSC 52
based clipboard write as the copy path.

The documented "hold Shift to bypass" escape hatch is a convention
supported by many native terminal emulators (iTerm2, Windows Terminal,
Kitty, etc.), but does not appear to be implemented by code-server's
bundled xterm.js terminal component. This leaves users of Claude Code
inside code-server (or other web-based IDE terminals using xterm.js)
with no way to copy terminal output while fullscreen mode is on.

Workaround

Removing "tui": "fullscreen" from ~/.claude/settings.json (or
otherwise reverting to inline rendering) restores normal native text
selection and copy, since Claude Code no longer requests mouse
tracking.

Suggested fixes

• Detect terminals/environments where the Shift-bypass convention isn't

supported and fall back more gracefully (e.g. don't suppress native
selection unless OSC 52 copy is confirmed to work).

• Document this known limitation for browser-based/xterm.js-hosted

terminals (code-server, Theia, etc.) so users know to disable
fullscreen mode there.

• Consider a keyboard-only copy command that works regardless of mouse

capture state (independent of terminal-specific Shift conventions).