[FEATURE] Desktop app: setting to auto-expand Edit/Write diffs by default

Feature Request

In the Claude Code desktop app, Edit/Write tool calls render with the diff collapsed by default. Reviewing a conversation that contains multiple edits requires clicking each diff card individually to see what changed.

Add a setting (e.g. desktop.diffs.expandedByDefault: true in ~/.claude/settings.json, or a toggle in the desktop app preferences UI) that renders every Edit/Write diff in the expanded state from the start.

Use Case

When reviewing a session — either live as Claude works, or scrolling back through a completed conversation — I want to see what was changed without clicking. The collapsed-by-default behavior optimizes for vertical density at the cost of every-diff being a manual interaction. For users who care more about reviewing changes than skimming a long transcript, the inverse default is more useful.

This is especially noticeable in sessions with many small edits (refactors, fixups, codegen passes) where the cost of expanding each one adds up quickly.

Suggested Behavior

• A user preference (settings.json key and/or preferences UI toggle) that defaults all Edit/Write diff cards to expanded state on render.
• Should apply to both pending approval prompts and completed tool results.
• Individual diffs remain manually collapsible/expandable as today; the setting only controls the initial state.

Prior Art / Related Issues

• #48744 (open) — "Add 'Expand All' / 'Collapse All' buttons for diffs in the desktop app." Adjacent but distinct: that's a manual one-shot action, this is a persistent default.
• #33562 (closed) — "Option to expand code diffs by default." Exact-title match for this request, but auto-closed as a duplicate of #33412 (which is actually about suppressing diff output in the terminal — the opposite direction). The dedup was incorrect; the request was never properly addressed.

Environment

• Claude Code version: 2.1.145
• OS: macOS 15.6.1 (Darwin 24.6.0)
• Surface: Claude Code desktop app