What are guardrails in the context of OpenAI application development?

from agents import Agent, Runner, GuardrailFunctionOutput, InputGuardrail
from pydantic import BaseModel

# Define a guardrail that validates math homework requests
class HomeworkCheck(BaseModel):
    is_homework_question: bool
    reasoning: str

guardrail_agent = Agent(
    name="HomeworkGuardrail",
    instructions="Check if the user is asking for homework help.",
    output_type=HomeworkCheck,
)

async def homework_guardrail(ctx, agent, input):
    result = await Runner.run(guardrail_agent, input, context=ctx.context)
    if result.final_output.is_homework_question:
        raise GuardrailFunctionOutput(
            output_info=result.final_output,
            tripwire_triggered=True,  # block the request
        )
    return GuardrailFunctionOutput(output_info=result.final_output)

# Attach guardrail to the main agent:
main_agent = Agent(
    name="TutorAgent",
    instructions="Help students learn programming concepts.",
    input_guardrails=[InputGuardrail(guardrail_function=homework_guardrail)],
)

# For irreversible agent actions - require human approval:
def confirm_database_write(action_description: str) -> bool:
    print(f"Agent wants to: {action_description}")
    return input("Approve? (y/n): ").lower() == "y"