Implement a Feature with Four Progressive Levels (Meta OA)

Problem: Implement a Feature with Four Progressive Levels (Meta OA) Your Meta Online Assessment is not a classic algorithm problem but a feature-implementation task. The prompt typically defines Level 1 to Level 4 requirements, and you must progressively extend the same code while keeping all previous levels working correctly. Implement the feature described in the prompt: Level 1: Implement the core functionality for the simplest scenarios. Level 2: Extend Level 1 to support additional capabilities (e.g., more input types, more operations, stronger validation). Level 3: Add more complex constraints (e.g., thread safety, performance targets, dedup/caching, ordering/consistency rules, robust error handling). Level 4: Further extend Level 3 (e.g., batch requests, rollback/undo, permissions, persistence simulation, complex queries). What to submit Implement the required interfaces (functions/classes/modules) in the allowed language. Pass the provided examples and hidden tests. Constraints and complexity Follow the constraints in the prompt. If none are given, avoid obviously inefficient approaches (e.g., repeated O(N^2) scans) and aim for near O(1) or O(log N) operations where applicable. Note: The original post does not include the actual feature description (what to implement, the four levels, I/O format, constraints), so this is a standardized restatement template for this OA type. Without the missing details, a concrete fully-specified coding question with tests/solutions cannot be reconstructed.