Preview
Preview shows the configured solid in the browser after a successful generate.
What you are looking at
The viewer displays a mesh (STL) derived from the Fusion rebuild. It is for visual confirmation — not the manufacturing file. The manufacturing file is STEP (plus DXF when the process class requires it).
When preview updates
Preview updates after Apply / Generate succeeds. Slider motion alone does not rebuild Fusion. That keeps mid-call sizing cheap and reserves the work item for intentional generates.
If geometry status reports Fusion live as off, the viewer will not invent a model. Fix credentials or wait for a warm production path before a customer demo.