[Feature] Native diff view for Claude Code AI edits (Cursor-style)

[RA1NCS]

Feature summary

When Claude Code writes output or edits a file, there's currently no automatic diff view. In VS Code with the Claude Code extension, every AI-generated file change automatically opens a split diff (or inline diff) in the editor so you can review what changed before accepting it. Athas doesn't have this yet, and it's a significant gap for AI-assisted workflows.

Requested behavior

• Every time Claude Code writes or modifies a file, the relevant file should automatically open in a diff view alongside the edit
• The diff should support both a side-by-side split view and an inline diff mode, with the user able to set a preference
• The diff view should show the full file context, with changed lines clearly highlighted (added/removed/modified)
• Ideally, there should be accept/reject controls per-hunk or per-file, similar to how Cursor handles it in non-auto-apply mode

Why this matters

Reviewing AI edits without a diff view means either manually checking git diff after the fact, or accepting changes blindly. The diff-first review flow is arguably the most important UX pattern for safe AI-assisted coding, and it's one of the primary reasons Cursor has the workflow feel it does.

Implementation context

Since Athas is built on Tauri (Rust + React) rather than Electron, it doesn't inherit VS Code's built-in diff editor from Monaco. The diff rendering would need to be implemented directly, either by building a custom diff component in React (using a library like diff or diff2html for the diffing logic and rendering), or by integrating Monaco Editor as the diff renderer specifically for this view. The Claude Code integration layer would need to emit file-change events that trigger the diff view to open with the before/after content.