# Enhanced file panel — diff display modes, inline comments, and in-browser file editing

## Why

BooCode's right-rail file panel has a solid foundation: a file tree (read-only), a Git diff tab
with unified display and stage/commit/discard. But it lacks features users expect from a modern
code review surface:

1. **Side-by-side diff** — was deferred under YAGNI in v1. The current unified-only view is hard
   to read on wide files and wastes horizontal space on desktop.
2. **Hide whitespace** — meaningless whitespace changes clutter diffs in code-generation workflows.
3. **Wrap long lines** — unified diffs of long lines require horizontal scrolling.
4. **Expand/collapse all** — only per-file expand exists; bulk toggling is missing.
5. **Inline diff comments** — was explicitly out-of-scope in v1. The user cannot annotate diffs.
6. **In-browser file editing** — the file tree is read-only. Editing requires agent tool calls or terminal.

## What Changes

### Frontend

- **GitDiffView.tsx** — toolbar row with: Unified/Split toggle, Hide whitespace toggle, Wrap lines
  toggle, Expand/Collapse all, Refresh (existing)
- **Diff rendering** — split-layout renderer (two panels side-by-side, aligned line numbers),
  CSS `pre-wrap` for wrapped lines
- **Inline comments** — `InlineReviewGutterCell` (hover → + button), `InlineReviewThread`,
  `InlineReviewEditor` (textarea saved via Zustand store)
- **Comment storage** — Zustand store persisted to localStorage, keyed by diff context
- **File editing** — double-click file in tree → inline textarea → Save/Cancel → server write API
- **Preferences hook** — `useDiffPreferences` → `{ layout, wrapLines, hideWhitespace }`

### Server

- **`git_diff.ts`** — add `ignoreWhitespace` param, pass `-w` to `git diff`
- **New route** — `POST /api/projects/:id/write_file` with pathGuard security

### Infrastructure

- No DB changes — comments client-side, file writes to disk
- No new WS frames — uses existing `git_diff_refresh` event
- No `@boocode/contracts` changes

## Risk

- **Side-by-side diff rendering** — biggest rendering risk; Paseo's `diff-layout.ts` is the reference
- **Inline comments** — lost on localStorage clear; acceptable for v1
- **File editing** — last-writer-wins for single-user is acceptable
