Function prepare_child_runtime_config 

pub fn prepare_child_runtime_config(
    parent: &VTCodeConfig,
    spec: &SubagentSpec,
    parent_model: &str,
    parent_provider: &str,
    parent_reasoning_effort: ReasoningEffortLevel,
    max_turns: Option<usize>,
    model_override: Option<&str>,
    reasoning_override: Option<&str>,
    resolve_model: impl FnOnce(&VTCodeConfig, &str, &str, Option<&str>, Option<&str>, &str) -> Result<ModelId>,
) -> Result<(ModelId, ReasoningEffortLevel, VTCodeConfig)>