Feature request: side-by-side diff option for Edit/Write/MultiEdit confirmation prompts

Summary

Add a setting to render the diff in the Edit / Write / MultiEdit confirmation prompt as side-by-side (before / after columns with character-level highlights) instead of the current stacked unified diff.

Current behavior

When the agent proposes a file change, the confirmation prompt shows a stacked unified diff:

6 -Old line of text here.
6 +New line of text here.

For long lines or refactors that move blocks around, this is hard to scan at a glance.

Proposed behavior

Add a setting in ~/.claude/settings.json (and /config):

{ "editorDiffStyle": "side-by-side" }

Possible values: unified (default, current behavior) and side-by-side. Render with the same character-level highlights git-delta --side-by-side produces.

Alternatives tried locally

• PostToolUse hook piping git diff to delta --side-by-side — works, but renders after approval, not in the confirmation prompt itself.
• PreToolUse hook writing rendered output to /dev/tty — fragile. Claude's TUI redraws (e.g. on terminal resize or when alternate-screen takes over) clobber the output, so the side-by-side disappears unpredictably.

A native toggle would solve both: rendered before approval, and not fighting the TUI for control of the screen.

Use cases

• Reviewing wording changes in long Markdown lines
• Refactors that move blocks of code around
• Edits where character-level highlights matter (e.g. Clojure keyword tweaks)

Environment

• Claude Code v2.1.132
• macOS, zsh