The previous code result = await Runner.run(guardrail_agent, input_data, context=ctx.context) is correct. This run is used inside homework_guardrail function and which is further passed to the triage agent ininput_guardrails. This run will run in parallel to the main result = await Runner.run(triage_agent, "who was the first president of the united states?") and result = await Runner.run(triage_agent, "what is life").
Therefore, the previous code is correct. No need to change guardrail_agent to agent. Please review.