[ziqq]

Changed files now offer a Unified / Side-by-side switch in in-page file tabs and View full. Side-by-side aligns old/new change blocks and synchronizes vertical and horizontal scrolling. Switching layouts reuses the validated revisions and syntax tokens while preserving the source line and fractional scroll offset.

The layout is shared within the page and defaults to Unified after reload. Tabs and View full keep independent positions; tab metadata remains in unified coordinates so file/review switches, Refresh and reload restore the same source location. Both panes remain virtualized, and closing or replacing a viewer removes its controls and listeners.

Validation:

• npm run verify: 253/253 tests, formatting, lint, static checks, build and ZIP verification passed.
• Added 20 regressions for layout controls, unequal change blocks, two-axis scroll synchronization and bounds, source-line positions, per-file/review restoration, inline/dialog isolation, font/viewport changes and disposal.
• All 20 new scenarios fail on the pre-feature implementation. Mutation checks detect disabled synchronization, lost source anchors and unequal horizontal overflow.
• The regression fixtures use production content factories with controlled provider replies and synthetic viewport geometry. Installed-extension smoke verification on live GitHub/GitLab remains pending.