Your question is Timer Design with Callbacks Header. 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).
Write a header file for a timer design using callbacks.
Asked in the round 1 stage. Provide a practical C or C++ header suitable for embedded software. Define the public timer types, callback signature, configuration, lifecycle operations, one-shot and periodic behavior, error reporting, and ownership rules. State assumptions about callback context, thread safety, cancellation, and callback lifetime. Keep implementation out of the header, but make the API precise enough to implement and test.