Your question is Edge Cases in Feature Storage. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
How do you handle edge cases when implementing a custom data structure for feature storage?
Discuss how you would define the data structure's contract before implementation, including behavior for missing keys, duplicate entries, invalid values, type mismatches, empty input, updates, and concurrent access. Explain how you would validate the implementation and preserve its invariants.
Scope: answer using a language and runtime you know well, with emphasis on practical implementation and testing decisions.