Function validate_bootstrap_composition 

pub fn validate_bootstrap_composition(
    model: &ModelProto,
    target_name: &str,
) -> Result<(), CompileError>

Walk the bootstrap-call graph rooted at <target>__bootstrap and verify every reachable Call resolves to an existing FunctionProto.

target_name is the root function’s name (i.e. the body half of the top-level Module). Models whose root Module has no bootstrap recording are no-ops — the trait’s default fn bootstrap(&self, _g: &mut Graph) {} emits an empty bootstrap that Module::build drops on the floor.