Exception Chaining

When a low-level failure causes a higher-level failure, there's a choice about which exception the code throws to the caller. Throwing only the high-level one loses the original stack trace, which is the main clue about what actually went wrong. Throwing only the low-level one leaks implementation details that the caller never agreed to know about. Exception chaining is the middle path: throw a new exception that fits the layer's abstraction and attach the original as its cause. The original stack trace is preserved, the caller still sees the API it expects, and the printed trace shows the full layered story.