A flick through the feed no longer drags background work through the middle of it. "When I flick to scroll, it's not getting up to speed very quickly, and clicking around in the app feels a bit sluggish at times" (Adam, 2026-11-07). Measured on his Pixel 9 in the installed PWA: idle is quiet (0.16 s of script in 10 s), but three real flicks through Following spent 1.7 s of 9 on the main thread, frames up to 200 ms, and the work was the avatar thumbnailer finishing faces as they scrolled in: a synchronous canvas.toDataURL WebP encode per face (229 ms), the profile cache JSON.stringified twice per half-second flush (once just to measure it, up to ~2 MB with thumbnails), and a whole-page repaint per finished face that changes nothing on screen (feed rows keep the face they were admitted with). Now: the crop, resize and encode happen off the main thread (createImageBitmap with resizeWidth/Height, OffscreenCanvas.convertToBlob, FileReader), with the old canvas path as the fallback; a finished face is recorded once the page settles; scheduleRepaint holds while a finger is down or the page scrolled in the last 200 ms (at most 1.5 s), and the profile flush likewise (at most 5 s, forced on an account switch) and sizes the blob by summing rows instead of stringifying it. Tests: the create flow's heads-up / passphrase / check steps from earlier today broke every test that made a wallet by waiting for the words and clicking "Skip verification"; tools/puppeteer.js exports seedWords() and skipSeedCheck() and the 96 tests use them. room-faces and avatar-profile fail the same way on 8858591 (row.hover, scrollIntoView), before today's changes

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01VMan6Ts5Tktega8VbLg31q

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