swift-concurrency-reviewlisted

# Swift Concurrency Review The Swift-concrete checklist for a dedicated concurrency pass over a branch diff. Each item is a bug class that has shipped past general review; the general design pass (`design-review-lens`) does not cover them. - **Actor reentrancy**: any state read before an `await` and used after it must be re-validated — the actor processed other work during the suspension. A guard checked before `await` proves nothing after it. - **`CheckedContinuation` discipline**: resumed exactly once on every path (including error paths); never leaked (an abandoned continuation suspends its task forever); never assumed cancellation-aware — `Task.cancel()` does NOT resume a checked continuation, the code owning it must resolve it on cancel explicitly. - **Terminal-state races**: periodic observation/progress loops must be stopped *before* a terminal state is written, or a late tick clobbers it. - **Cancellation propagation**: long async sequences check `Task.checkCancellation()` at the top and between phases; work that must not outlive its owner is not `Task.detached`. Never swallow `CancellationError` with `try?` around `Task.sleep` — catch it and stop. - **Callback ordering**: delegate callbacks arriving on framework queues that hop to `@MainActor` via `Task` lose ordering guarantees — two hops can land inverted. Any logic that depends on arrival order needs a single serialization point. - **`@unchecked Sendable`**: justified only by all-immutable st