This practice set combines the advanced units on unfamiliar workloads. The exercises ask you to protect a concrete invariant or user objective when two systems disagree about what happened. You'll identify lost updates, preserve publication intent, bound launch traffic and choose a safe recovery action.
A final design needs to admit its limits. An asynchronous replica can expose a loss window. A provider timeout can leave an unknown payment outcome. A cache or search index can help find an item without owning the right to sell it. Work through those boundaries explicitly. When a task asks for a number, keep the requested units and avoid adding unrequested headroom. When it asks for a reason, choose the one tied to the stated failure rather than an unsupported promise about a component.