- busyReason had no reader: the chat engine sets isBusy through the store's
generic set, like every other flag.
- The isSameDocument comment says the two "same document" rules disagree
in both directions, so neither is a subset of the other.
- The import boundary test bundles minified with one pako (the MCP core
resolves its own copy) and caps the canvas core at 160 KB (134 KB now).