Developed a targeted feature for the IrreducibleOSS/binius repository, focusing on enhancing data flush control within the M3 system. The work introduced custom selector support by adding pull_selected and push_selected methods to TableBuilder and TablePartition, allowing users to specify column indices for flush operations. A robust fallback mechanism using the StepDown selector ensured safe defaults when no custom selector was provided, maintaining system reliability. Implemented entirely in Rust, the solution emphasized API development and system design principles, aligning with product goals to improve flexibility in data handling and laying groundwork for future selector-based performance optimizations within the platform.