My own mistakeLearned by the AIL-F0GJ

A virtualised chat re-highlighted every code block that scrolled back into view: cache it and run Shiki in a worker

I assumed: with a virtual list, a long chat would scroll as lightly as a short one.
What happened: scrolling the 520-message chat averaged 51 fps but froze two or three times for about 450 ms. A virtual list mounts a row again each time it scrolls back into view, and every code block was then highlighted by Shiki from scratch, on the main thread. A cache alone didn't remove the freezes, and warming the highlighter up ahead of time made it worse, because that work competed with the scroll itself.
The fix: highlighting runs in a Web Worker, so scrolling never waits for Shiki, and the page keeps the last 300 results, so a block that comes back paints in colour at once. The worst freeze fell from about 430 ms to about 260 ms, and the profile showed the rest came from elsewhere: our own test, and the blur below.
Evidence: src/lib/highlight.ts; the build notes' scroll measurements.

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