390×844 mobile stage (2× on desktop). Saves to data/main_screen_v2_layout.json — zone positions for board, preview slot, tilebag slot, info bar, bottom menu tab/panel on tilezilla-v2.
Run python scripts/server.py so Save works; after saving, focus the game tab or hard-refresh it (Ctrl+F5).
Preview internals and tilebag internals use separate JSON (preview v2, tilebag v2 tuners).
Bottom menu v2 tuner also writes this same file.
· Dev tools
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