This is an early reference to transitively immutable. I transmogrify a point made there that seeing the private RSA key of a bank leads to the ability to cause great mischief even though it is highly immutable.

Here are some possible meanings:

  1. Access to something that is guaranteed to be the same in the future as it is now. (durable)
  2. Access via which you cannot cause a thing to change. (read-only)
  3. Access via which you cannot cause a thing to change but can acquire access like this. (sensory)
  4. Access to something unchangable in one or both of the above senses, but via which you can acquire access which does not conform to any of these limitations.
It seems clear that this list is neither orthogonal nor exhaustive. The sensory key is number 3. With a requestor's key to a discreet factory, one can gain access to mutable objects but it is nonetheless incapable of providing egress for data, for the mutable object is itself confined.

I won't propose terms for these but dead end might be a category for the factory requestor's key.