Tiny World Visibility — Sticky Preview Reveal

The opacity torch is gone. The home board is always fully rendered; Preview cells reveal one-by-one as the camera pans into them, and stay revealed forever after that (a breadcrumb trail behind the user).

Mental model:

• Every user has one editable home board (size GRID, default 8).
• The home GRID x GRID region is always at full opacity, full color, full scale — never fades, never pops.
• Preview boards surround the home board and preview other users' content.
• Nothing is rendered in grayscale — all tiles use their full color.
• A Preview cell is hidden until it enters the visible square around target.x/z (renderVisibleSize wide). Once revealed, the cell is sticky: root.userData.revealed = true and it stays revealed for the rest of the session. Its final display opacity is controlled by the user-facing Preview opacity / floors / objects sliders.