Prerequisite Diagnostic

Attempt before the pattern lessons. This checks programming, ownership and contracts already taught in Modules 1–3; it does not require knowing this module's pattern names.

1. A function accepts a callback that returns a price. Show how a fake callback records the number of calls. What would two invocations change if the callback had an external effect?
2. Two variables refer to the same list. Predict both observations after appending through one name. Then explain a shallow dictionary copy containing that list.
3. A constructor opens two resources; the second acquisition raises an exception. Identify what exists and who must release it. A cleanup plan is not an executed cleanup.
4. A test asserts only the final total. Explain which ordering, ownership or exception defects could still escape it.
5. A command is rejected before any state change. Explain why previously valid undo/redo state should remain intact under the earlier editor contract.

Record independent / with help / needs repair per item. Repair callback contracts in Module 1, characterization tests in Module 2, and lifecycle/history in Module 3. Use one new example after repair. Do not restart a whole earlier module because you cannot name Adapter or Builder yet. Diagnostic calibration is for after the attempt.