Restores the coverage floor (94.85% → 95.19%). The diff-panel work landed
with diff_view.dart at 59% — the hunk header, the addition/removal/context
line rows, the new/deleted/renamed/binary metadata, and the error and
empty-state branches were never exercised. Adds four widget tests over an
injected controller; diff_view.dart goes 59% → 96%.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Adds diff as a fourth ui.open target. The diff extension now retains an
app-scoped DiffController and subscribes to its builtin.diff/selection
channel: a selection reveals the diff tab and focuses the file, which
the view scrolls into view and highlights. Retaining the controller in
the extension (not the view) lets a focus survive the tab being
revealed/remounted, mirroring the ReaderNav viewers.
Closes T-233.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
jpmschweitzerandClaude Opus 4.8