Make the sandbox easy to start, easy to extend internally, and safe to mutate. Prerequisite milestone for larger editor tools.
Make project content user-organized and production-like: file-manager operations, destination-first imports, path-agnostic stable registry/runtime catalog, static/skinned model material mapping and extraction, immutable DefaultGrid plus project fallback, live refresh, headless processing, reference repair, and completed runtime property blocks.
Add larger-world authoring and practical prop placement: terrain sculpting plus physics drop/settle.
Make Blacksite trustworthy for daily production: transactional scene writes, autosave and crash recovery, hardened hierarchy/prefab workflows, project launch/templates, asset integrity, and persistent editor sessions.