fix(scroll): suppress pin-bottom repaint during MAM catch-up#925
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…once on completion Entering a room that needs forward MAM catch-up pages in history over ~1-2s; each merge grew scrollHeight and forced a WebKit repaint (~12ms) on every re-pin, so the bottom-follow loop never converged within its frame budget and the view visibly jumped once catch-up finally settled. The repaint is now suppressed while isLoadingOlder is true (WebKit never painted those intermediate positions anyway), and a single clean settle pin fires once catch-up completes.
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Summary
scrollHeightand forced a WebKit repaint (~12ms) on every re-pin, so the bottom-follow loop never converged within its frame budget — producing a visible jump once catch-up finally settled.shouldForceRepaintnow takes asuppressForBackgroundLoadflag: the forced repaint is skipped whileisLoadingOlder(MAM query in flight) is true, since WebKit never painted those intermediate positions anyway.isLoadingOldertransitions true → false while the reader is at the bottom, so the final position always lands correctly even when the last MAM page brings no further message-count change.