Lived-In by Design: Behavior-Grounded 3D Scene Generation via Functional-Group Assembly

We present Lived-In by Design, a framework for behavior-grounded agentic 3D scene generation by carrying everyday-activity context from prompt interpretation to room-scale layout. Unlike existing methods that construct scenes primarily from object inventories and pairwise spatial relations, our method models the functional dependencies and human-use constraints that organize objects in inhabited environments. Specifically, we first design a behavior-to-asset stage to convert plausible activities generated by agent into object requirements, quantities, shared resources, and functional relations. To preserve these relations during construction, we further introduce functional-group assembly, which organizes related objects into behavior-dependent local configurations. Finally, we design a lived-in scene layout stage to place these groups jointly at room scale while considering architectural constraints, accessibility, and human usage space. Evaluations on 179 room-level prompts using automatic metrics, qualitative comparisons, controlled ablations, and human judgments demonstrate improved functional organization and lived-in plausibility.