OK, guys, I'm completely stuck.
My (single-class) mage main character has finished the sphere (valygar quest) and did not get the option to have it as a keep. When I carried out Lavok, he did not "give" it to me, nor did I meet any cowled wizards there (even days later).

My guess is that I either fouled up something or I've hit a bug. I'd really like a keep!
If this IS a bug, how might I be able to get it anyhow? I really don't wish to restart.
Any ideas?

? Try entering the keep. If nothing happens. I have no idea.

Been there, done that.

I think I'm pretty convinced that I have hit a bug. What I'm left wondering is this - I've heard people mentioning "cheating" to get more than one keep - how is this done? I simply want to get ONE!

Use the MoveToArea cheat and find out which area it is. (You can find it out at www.tgeweb.com/ironworks/baldursgate2) Goto the cheat section I think and then the area list. It might have it there.

The problem isn't getting in - I can do that easily enough. The problem is in getting it assigned to me as a keep.

I imagine that Shadowkeeper can do this - there is an area which assigns values to certain actions, such as keeps. I just don't know what values to enter!

the hint book states you must bring lavok outside so he can see his world for one last time. no idea what that means, I'm still trying to crush the cult of the unseeing eye...
it also says he'll hand over the sphere to be your new wizard's batcave...

I was under the impression you had to deliver the Knights of Solamnia back to their home plane before you could take the sphere as your own.

Well, if I must return the knights, then I definitely blew it. The sphere cannot be moved after it returns to Athkatla. However, I do not recall getting the option as to where to move it - nor do I have a save prior to returning.
As for Lavok, I did bring him out. He did not give it to me.

As said before, I am pretty sure I either blew it or found a bug. Does anyone know how to get it through Shadowkeeper or other means?

1.go talk to the knights.
2. go to Ribald.
3. Come back.

The planar sphere's dead. You're not meant to use it to sent the knights home, you have to find another way.