Function builtin_director 

pub async fn builtin_director(
    args: &[DslValue],
    ctx: &ReasoningBuiltinContext,
) -> Result<DslValue>

Execute the director builtin: decompose + delegate + synthesize.

Arguments (named via map):

• orchestrator_prompt: string — system prompt for the director
• workers: list of maps with {name, system} — worker agent definitions
• task: string — the task to accomplish

Returns a map with keys: result, plan, worker_results.