The navigator re-rendered the whole document on the UI thread on every revision, including
each drag step, and layer thumbnails re-rendered whole layers the same way. Both now keep the
last image while an interaction runs, render on a background worker once the document settles
(synchronously on wasm and in tests), and turn on image mips. Thumbnails are keyed by node id
with a Weak, not by a reusable address.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VmMmc1J8XeNLxhRihWv9cc