InstallStream.getPackage() returns unimplemented

[zenhack]

Package installation via the UI works now, but the call to getPackage() is returning an unimplemented error for reasons I don't yet understand -- the method is indeed implemented on the server side, but print debugging reveals that the method is never actually being called. As a result, we get an error message and the package isn't added to our app list until we refresh the page.

[zenhack]

I'm hitting something similar with a call to viewsPuller.Sync. It's definitely implemented and definitely not being called. I'm starting to suspect a go-capnp bug (cc @lthibault)

[zenhack]

Note that in both of these cases we're calling the failing method on a promise, so that's probably important.

[zenhack]

I pushed a workaround for these, just waiting on the necessary promises. I'm going to keep this open though, since it's not a proper solution.

[zenhack]

I opened capnproto/go-capnp#521 to track the underlying issue.