Proposal to add a method:

<U extends T> BeanBuilder<U> produceConstant(U instance);

This would be a shortcut so the common case when an existing instance whose lifecycle is not managed by CDI is exposed to CDI so instead of

Foo existing = getFoo();
builder.produceWith(() -> existing)

you can use

Foo existing = getFoo();
builder.produceConstant(existing)

The name is terrible and should really actually implement a better one. I can only think of:
produceConstant()
produceSingleton()
produceInstance()
produce()

at the moment but neither of them seems right so we should keep searching for a good one.