[FEATURE] Desktop: side-by-side (split) mode in the diff viewer, alongside the current inline view

Preflight Checklist

• [x] I have searched existing issues and this hasn't been requested yet
• [x] This is a single feature request

What Problem Does This Solve?

The Desktop diff viewer renders changes inline only. There is no way to switch to a split, side-by-side view with the old version on the left and the new one on the right.

Inline is a reasonable default for small edits, but it is the wrong shape for the reviews where the diff viewer matters most: a rewritten function, a reordered block, a file where an argument changed on twenty call sites. Reading those inline means mentally reconstructing "before" from interleaved - lines. Side-by-side is the standard display mode in GitHub, GitLab, VS Code, and every JetBrains IDE precisely because it makes that class of change legible at a glance.

This matters more in Desktop than in the CLI. Desktop is positioned for exactly this workflow — the docs say to "use Desktop when you want to … review changes visually" — and the diff viewer is already a serious review surface, with per-line comments that Claude reads and acts on, plus a Review code action. It is the one review UI in the product without a display-mode choice.

For anyone who moved off an IDE and now relies on Desktop for reading diffs, this is a step down from the tool they left: JetBrains IDEs open diffs side-by-side by default.

Proposed Solution

A toggle in the diff viewer's toolbar to switch between Inline and Side-by-side, remembered across sessions. Ideally it also applies to the per-file diffs shown as Claude edits, not just the full diff view opened from the +12 -1 indicator.

Per-line commenting should keep working in both modes — that is the feature that makes this viewer worth using over an external tool.

Current State

There is no hidden setting for it. app.asar contains no diffMode, splitView, sideBySide, or split-view strings; the only occurrences of "side-by-side" are unrelated diagram-authoring text, and "unified" appears only inside a bundled Microsoft Graph SDK. The docs describe a single layout — "a file list on the left and the changes for each file on the right" — with no mention of a view mode.

The phrase "side by side" in the docs refers to arranging panes (chat, diff, browser, terminal, editor) in the workspace, which is a different feature and already works well.

Environment

• Claude Desktop: 1.24012.11 (Linux beta, apt)
• Not platform-specific