Carry the sx-vm-extensions loop's serving-JIT handoff notes, and add a
correction: the post-page slowness was the durable read count (fixed in
0a2f1a61), not the (long-gone) Smalltalk render path — so SX_SERVING_JIT is an
optional general speedup, not the perf blocker.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
