The changes builder getters now assert that their context was given,
but prepare-restore-component and generate-delete-shapes relied on them
returning nil to fall back to other data. The workspace restores
components with changes that carry no library data, so restoring a
main component or a variant from one of its copies failed.
Add has-library-data?, has-objects? and has-page? to the changes builder,
and check them in those fallbacks before calling the getters.
Add tests that restore a component, and a variant whose container was
deleted, with changes that carry no library data, as the workspace does.
AI-assisted-by: claude-opus-5-5
ae1b541208