Extend and optimize an existing CLI tool

You are given: - A short requirements doc for a command-line (CLI) tool that performs a set of concrete tasks (subcommands, flags, inputs/outputs). - An existing codebase that partially implements the tool. ### Tasks 1. **Understand the current implementation** - Read the codebase and explain the current architecture (modules, data flow, error handling, parsing of arguments, I/O boundaries). 2. **Gap analysis vs. requirements** - Identify which required features are missing or incorrectly implemented. - Prioritize what to fix/implement first. 3. **Implement missing features** - Add the missing functionality while keeping the code maintainable and consistent with existing style. - Add/adjust tests (unit and/or integration) to validate the behavior. 4. **Optimization and quality improvements** - Point out performance bottlenecks or unnecessary work. - Propose and implement at least one improvement (e.g., avoid repeated parsing, reduce I/O, simplify hot paths), without breaking correctness. ### What to discuss during the interview - Trade-offs you make while changing an existing codebase. - How you prevent regressions (tests, logging, incremental refactors). - Edge cases (invalid arguments, empty input, large input, error propagation).