[racket] instantiating multiple sandboxes with gui's

>> How does this handle dynamic and lazy requires?

It doesn't.

> Also: how do you know if the cache is stale?

I don't.

So my other idea was to do what dynamic-rerequire does and
parameterize current-load/use-compiled, and examine the dependencies.
However in the case where it detects racket/gui/base being loaded for
the first time, it would somehow need to abort the load,
dynamic-require racket/gui/base on the main custodian, then restart
the load as usual. That felt icky, so instead I tried the above, but
if it's the only way to handle dynamic and lazy requires, it's the
only way.