Flash-free scroll restore on open (editor + chat) + chat batch-load fixes#2276
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…undation + editor)
On re-open the previous messages are still cached and rendered by the time a useLayoutEffect runs, so scroll straight to the target (last-read message, else bottom) BEFORE the first paint — the first frame is already positioned, with no stale 'past' frame and no jump, matching the editor's pre-paint restore. No hide or delay. init() refreshes asynchronously and re-confirms the same target; Chromium's overflow-anchor keeps the viewport stable. Keyed to the chat subId so in-place chat->chat switches re-position and same-chat dependency churn doesn't. Cold opens (no cache) fall through to init()'s normal async positioning.
…ndow) loadDeps destroys and re-subscribes the whole per-chat deps subscription to only the ids it is given. The batch-load paths passed only the NEW page, so already-loaded messages' image/file attachments were dropped from S.Detail and their images vanished on every batch load. Subscribe deps for the full window (existing + new) in loadMessages and subscribeMessages(non-clear), matching the live-message path (onMessageAdd) that was already correct.
The 'load older' prefetch is scroll-event driven (fires when scrollTop is within ~1 viewport of the top), and the chat relies on the browser's overflow-anchor to hold position on prepend. But overflow-anchor is suppressed at scrollTop 0, so a fast scroll that reaches the hard top pins the view at 0: the prepend doesn't shift it down and no further scroll event fires, so pagination stalls. Fix: only at scrollTop 0, capture the top message before the prepend and restore its position pre-paint (useLayoutEffect on dummy), landing the view just below the newly-loaded batch — off 0 — so the prefetch keeps firing as you scroll. For scrollTop > 0 nothing changes (overflow-anchor still handles it). The head is never evicted by a prepend, so the anchor always survives.
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Why
Opening an object or chat restored the saved scroll after the content had already painted at the top → a visible flash + jump. This makes the restore happen before the first paint, so the first frame is already in the right place. While testing the chat side, three related batch-loading bugs surfaced and are fixed here too.
Editor
useScrollRestorehook): save the topmost-visible block + offset on scroll; on open, position synchronously inuseLayoutEffect(before paint), anchored to the element so it stays exact even as async content settles. BoundedResizeObserverre-pins through the settle window; legacy pixelgetScrollkept as fallback.#blockLastfiller measure so a near-bottom target is reachable on frame one; skipfocus.scrollon open when a saved scroll exists.edit.tsx) — unnecessary latency once restore is pre-paint.Chat
overflow-anchorholds it acrossinit()'s async refresh.loadDepsdestroys + re-subscribes the whole per-chat deps subscription; the batch paths passed only the new page, dropping already-loaded messages' attachments fromS.Detail. Now subscribe deps for the full window.overflow-anchoris suppressed atscrollTop 0, so a fast scroll pinned the view there and the scroll-driven prefetch couldn't re-fire. AtscrollTop 0only, anchor the top message and restore its position pre-paint so the view lands off 0 and loads keep flowing.Tests / verification
src/ts/lib/util/scrollAnchor.test.ts(restore math + settle tracker).bun run typecheck+bun run lintclean.Notes
docs/superpowers/.