The generated config failed the real loader (KeyError: cuda). It now copies src/CelerisLab/configs/config_lbm.json and overrides only grid, physics, collision/streaming/storage, y walls, LES off and uniform inlet profile; inlet scheme and outlet mode stay the template's and are recorded in case.json. New CPU test loads the generated file with load_lbm_config. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>