[BUG] Tab indents lose the background colour in fullscreen mode

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)
• [ ] I am using the latest version of Claude Code

What's Wrong?

In fullscreen mode (CLAUDE_CODE_NO_FLICKER=1), the cells that a tab character expands to do not get the background of the text around them. Claude Code writes ESC[49m (default background) before the tab cells and sets the background again only for the text after them. So the terminal's own background shows through as a hole

This affects every background that Claude Code paints under text. I saw it in a user message (userMessageBackground) and under the text selection (selectionBg). On a dark terminal with a dark theme, the hole is almost the same colour as the background, so it is easy to miss. With a light terminal and a coloured background, each tab indent shows as a white block

What Should Happen?

The cells of a tab indent should have the same background as the rest of the line

Error Messages/Logs

# tmux capture-pane -e of a user message "Reply with just OK.\n\tone tab\n\t\ttwo tabs",
# with a custom theme that sets userMessageBackground to #0D0E0F
ESC[38;2;175;175;175mESC[48;2;13;14;15m❯ ESC[38;2;0;0;0mReply with just OK.ESC[39m
  ESC[49m      ESC[38;2;0;0;0mESC[48;2;13;14;15mone tabESC[39m
  ESC[49m              ESC[38;2;0;0;0mESC[48;2;13;14;15mtwo tabsESC[39m

Steps to Reproduce

1. Create ~/.claude/themes/probe.json:

``json
{"name": "probe", "base": "light", "overrides": {"userMessageBackground": "#0D0E0F", "selectionBg": "#0A0B0C"}}
``

1. In tmux, start Claude Code with a message that has tab-indented lines:

``sh
tmux new-session -d -x 100 -y 30 "CLAUDE_CODE_NO_FLICKER=1 CLAUDE_CODE_TMUX_TRUECOLOR=1 claude --settings '{\"theme\":\"custom:probe\"}' \"\$(printf 'Reply with just OK.\n\tone tab\n\t\ttwo tabs\n')\""
``

1. After the reply, run tmux capture-pane -e -p and look at the lines with tabs
2. The indent cells have ESC[49m, and the text after them has ESC[48;2;13;14;15m

In a real terminal with a light background, the indent shows as a white block inside the coloured message. Selecting tab-indented tool output shows the same holes in the selection

Claude Model

Opus

Is this a regression?

I don't know

Claude Code Version

2.1.280 (Claude Code). The latest release is 2.1.283, and I did not test it

Platform

Anthropic API

Operating System

Other Linux

Terminal/Shell

Other

Additional Information

NixOS, kitty 0.49.0 for the visual report, tmux 3.7c for the capture above