The context document should automatically be marked as used in the AsyncContext

If you have an async script which only manipulate the current document through $doc, that document won't be automatically marked as used and won't be invalidated when this document is modified.

It's of course possible to explicitly mark it as used using the async script service but it seems to be common enough to worth an automatic use and (valid) use cases where you enable the context document without using it is probably rare.