[BUG] Fullscreen TUI in VS Code terminal: mouse drag-select works only once, next selection requires switching terminal tabs

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

In fullscreen TUI mode running inside the VS Code integrated terminal, mouse drag-to-select works only for the first selection. After that first selection is made (and auto-copied via copy-on-select), subsequent click-and-drag attempts do nothing - no highlight appears at all.

The only reliable way to make selection work again is to switch away to another VS Code terminal tab / Claude Code session and switch back. After that focus round-trip, exactly one selection works again, then the cycle repeats.

Steps to reproduce:

1. VS Code, integrated terminal, Claude Code with "tui": "fullscreen".
2. Click and drag over assistant output - selection highlights and is copied on release (works).
3. Release the mouse, then try to click and drag a different piece of text.
4. Nothing highlights. Wheel scrolling still works.
5. Switch to another terminal tab and back - selection works again, once.

Notes:

• Pressing keys to clear the (invisible) previous selection does not seem to restore drag-select.
• Shift+drag (VS Code native selection bypass) works every time, so this is specific to Claude Code's in-app selection state, not the terminal.
• Likely related to the mouse-capture family tracked in #81472, but I did not find this exact "works once, needs terminal focus round-trip" variant filed.

What Should Happen?

Every click-and-drag should start a new in-app selection, replacing any previous one, without needing to switch terminal tabs to reset state.

Environment

• Claude Code: 2.1.231
• OS: macOS (Darwin 27.0.0, arm64)
• Terminal: VS Code integrated terminal (xterm.js)
• TUI: fullscreen ("tui": "fullscreen" in ~/.claude/settings.json)
• Env: CLAUDE_CODE_SCROLL_SPEED=3; no CLAUDE_CODE_DISABLE_MOUSE* variables set
• Copy on select: enabled (default)