MAIN_MODEL_DEFAULT_SCOPE = DefaultModelScope(
noun='default',
hint='set default',
load=lambda: ModelConfig.load(Ctrl+S target for /model: the main agent model ([models].default).
Persisting is validation-free, but action_set_default refuses rows whose
provider integration is not installed (those can never build). -M/--model
outranks this key for a single launch.