* perf(app): keep large diffs responsive
Render file headers on the canvas and bound expensive text shaping to the active viewport while preserving sticky, hover, and horizontal-scroll behavior. Let native scroll cancellation arbitrate header presses so finger scrolling cannot expand files.
* test(app): assert canvas diff header accessibility
* test(app): assert canvas diff header semantics
Fast Refresh preserves refs while rerunning effects, so canceled paint requests must release their retained IDs or unseen diff regions stop rendering. Paint the final expanded body’s reserved boundary pixel because no following header owns that seam.
Keep diff headers and painted content on the same scroll clock while preserving native scrolling and independent per-file horizontal offsets.
Complete review, selection, typography, tree, and palette parity without returning line rendering to React.
Mohamed Boudra