How does coroutine cancellation work internally?

This tests your deep knowledge of cooperative cancellation in structured concurrency. A great answer explains that `job.cancel()` sets a flag, cooperative `suspend` functions check this flag at suspension points and throw `CancellationException`, and long-running, non-suspending computations must manually check the `isActive` property to become cancellable. A common red flag is assuming cancellation is preemptive, like a thread interruption, instead of a cooperative process that requires explicit check-in points.