The sync-frame guards (_fixMobileScrollJank / _suppressBrowserOverflowAnchor)
only cover the render frame itself. postProcessRenderedMessages() — syntax
highlight, inline diff/csv/pdf/html/excalidraw, katex/mermaid — is scheduled a
FRAME LATER via requestAnimationFrame(), after those guards have released. Each
of those can change the height of rows ABOVE the viewport; on mobile
(overflow-anchor:auto) the browser's native anchor engine then compensates
scrollTop a SECOND time in that unguarded frame, yanking an unpinned reader to
another turn (the residual mobile 往回大跳).
Wrap all three deferred post-process dispatches (fast-path cache branch, main
render tail, live-tool remount) in _postProcessWithAnchorSuppression(), which
routes through the shared _suppressBrowserOverflowAnchor() and holds suppression
one extra frame so late media/layout reflow is covered too. Desktop rests at
overflow-anchor:none so the wrapper is a verified no-op there.
Reproduced on an isolated debug instance with a cloned 1179-message session:
above-viewport +350px during the async settle window jumped scrollTop +350 on
mobile (auto) and 0 with the wrapper; desktop (none) 0 both ways. static/ui.js
only.
allenliang2022
7db6fd8650
