Smart Creation

Known types of objects should create subtypes of objects easily. For example, saving a whole Manifest should make Sequences and Canvases automatically. Resolving a Manifest may also need to dereference some stuff.

For unknown items or properties without `@type` declarations, we should be able to read the `@context` to unwind it a bit, if needed.

The issue names no files, tests, or entry points, so first locate the code that creates and resolves Manifest objects. Read how known types, unknown properties, and @context are currently handled. Done means saving a Manifest can create its declared subtypes and resolution can dereference the required data, while unknown items can use @context when needed.

Written by the indexing model from the issue text.