With block-level commit the open code fence grows by whole lines at the
throttle cadence, so the old reason to skip highlighting it (re-tokenizing
a growing block ~40x/sec) no longer applies: a partial fence now
highlights too, and streamed code arrives colored instead of colorizing
only when the fence closes. Fences beyond 300 lines fall back to plain
text until closed, keeping the repeated worker re-tokenization bounded.
A freshly committed block also enters with a short fade-and-rise. The
class goes on the block's children (the wrapper is display:contents and
cannot animate) and the transform is paint-only, so virtualized row
measurement is unaffected; reduced motion disables it.
Verified over CDP on a production build: streamed code inside a still-
open fence renders highlighted, and the code text's x-position is
identical during and after the stream.
Bohdan Triapitsyn
d71bcb5025