Terminal markdown renderer missing strikethrough and limited color support

Problem

The system prompt tells the model it can use GitHub-flavored Markdown:

"You can use Github-flavored markdown for formatting, and will be rendered in a monospace font using the CommonMark specification."

However, the terminal renderer has two significant gaps:

1. Strikethrough (~~text~~) does not render

GFM strikethrough syntax is silently stripped. The glow Markdown renderer handles this correctly in the same terminal (Ghostty), so it's not a terminal capability issue — it's the renderer.

2. Very limited color in output

Only 3 elements get any color treatment:

• inline code (blue)
• code blocks (syntax highlighting)
• Links (darker blue)

Everything else — headings, bold, italic, block quotes, list markers, horizontal rules — renders in the same default color. This makes it hard to visually scan long responses. Other terminal Markdown renderers (glow, mdcat, rich) demonstrate that much richer color treatment is possible.

I'll also note that only H1 renders with an underline. That could be used in more places for additional readability.

Suggested improvements

1. Render strikethrough — most modern terminals support SGR 9 (crossed-out). Consider falling back to Unicode strikethrough combining characters.

1. Add color to headings — could be different colors for h1-h6, or just a couple; anything to create visual hierarchy.

1. Color blockquote markers — dim or colored > prefix helps distinguish quoted content.

1. Color list markers — subtle color on -, *, 1. improves ease of scanning.

1. Table Headers — make them bold, and/or maybe add some color

Environment

• Terminal: Ghostty
• OS: macOS 26.3.1 (Tahoe)
• Claude Code: 2.1.84
• glow renders all of the above correctly in the same terminal

Related issues

• #26390 — Covered similar ground (closed as stale)
• #13600 — Broader markdown renderer feature request (open)