Proposal and authority are different roles
The producer is optimized to suggest useful application structure. The runtime boundary is responsible for deciding whether a proposed structure belongs to the supported execution surface. Combining those roles would let the same generative output both request and define its own authority.
Authority comes from the environment
Capabilities, permissions and supported operations are defined outside producer output. A graph can refer to known capabilities, but it cannot create a new executable capability merely by naming or embedding one.
Why arbitrary code changes the trust model
Arbitrary producer-written code is maximally expressive because it can introduce behavior that was not already represented by the closed capability vocabulary. Intent-space is specifically investigating whether useful software can be generated while keeping that escape hatch outside the producer's normal authority.
Bounded execution reduces expressiveness unless the capability surface grows. The project treats that cost as part of the thesis to evaluate, not as something to hide behind validation language.