[FEATURE] Support DejaVu Sans Mono font / limit output to characters in the currently active font.

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When using xterm with a common default font of DejaVu Sans Mono, such as on OpenBSD, Claude Code frequently makes use of characters lacking glyphs in the font. Xterm does not use multiple fonts to fall back on and instead puts a rectangle in the output.

The work-around is to install and use a different font. JuliaMono seems to have the necessary glyphs. However, Claude Code shouldn't need to always use/mis-use glyphs for decorative output. It would be useful if there was a configuration to restrict output to characters available in the currently active font.

Proposed Solution

Add a configuration option to restrict output to the characters having glyphs in the currently active font.

Alternative Solutions

Workaround is to use JuliaMono font.

Priority

Low - Nice to have

Feature Category

Interactive mode (TUI)

Use Case Example

Example scenario:

1. I am working on a system with a minimal footprint, such as OpenBSD, that has DejaVu Sans Mono and xterm (and tmux) as the terminal setup.
2. Install node and Claude Code.
3. Observe that Claude Code frequently makes use of characters than can't be rendered.
4. Changing the font to support these characters is more work.

Additional Context

_No response_