You are given an existing Python codebase that defines multiple classes, including abstract base classes using abc.ABC and @abstractmethod decorators. Without modifying public interfaces or abstract base classes, implement the missing logic in the concrete subclasses so that the system works end-to-end. Constraints:
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Honor the Liskov Substitution Principle; any place expecting a base type must work with your concrete types.
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Do not change method signatures, inheritance, or module-level APIs; implement only TODOs in concrete classes.
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Clearly separate responsibilities (e.g., parsing, validation, and execution) using composition where appropriate.
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Ensure correct handling of edge cases and error propagation as indicated by docstrings and type hints.
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Provide unit tests that demonstrate the behavior of each implemented class and key interactions.
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Briefly explain how you navigated a large (≈200 lines) skeleton with abstract methods to identify implementation points and avoid confusion.