Failures

• MissingValueError: a requested required field is unset.

• InterpolationError: contextual selection failed or a dependency cycle was detected.

• OwnershipError: attachment would create multiple owners or a structural cycle.

• FrozenError: a final/computed value was mutated, or a callback tried to mutate its resolving tree.

• ConfigError: field validation failed, export preceded finalization, or a value/normalization violated the config graph contract.

Unknown attributes raise AttributeError; unknown constructor keywords raise TypeError. User callbacks and checks retain their own exceptions. A failed finalization leaves the draft available for correction. Ownership changes validate the proposed attachment before modifying existing ownership.