Jan Schumacher enhanced the aws/amazon-s3-encryption-client-java repository by delivering a feature that ensures reliable S3 instruction file uploads with accurate content length handling. He updated the InstructionFileConfig component to derive the content length from the actual byte length of the instruction file, addressing issues with incorrect PutObjectRequest headers. Jan implemented this solution in Java, leveraging his expertise in backend development and AWS S3 integration. To ensure robustness and prevent regressions, he added comprehensive unit tests for both synchronous and asynchronous S3 clients. This work improved the reliability of S3 uploads, reducing edge-case failures and enhancing the overall customer experience.