A repository defines infrastructure with AWS CDK. Before deployment, operations wants to inspect the proposed infrastructure differences against the deployed stack. Which CDK command provides this review?

1. Run cdk bootstrap and assume its completion proves the application stack has no differences.
2. Run cdk synth and treat its generated template alone as a comparison with the deployed resources.
3. Run cdk destroy and use the deleted resource list as a safe change preview.
4. Run cdk diff for the target stack and inspect the reported changes before cdk deploy.