swift-concurrency

# Swift Concurrency Treat isolation and cancellation as API contracts. Compile under the project's real Swift language and strict-concurrency settings. ## Core rules - Prefer structured child tasks and task groups. Detached tasks require an explicit ownership and context-transfer justification. - Keep mutable shared state actor-isolated or otherwise synchronized; do not silence diagnostics with unchecked `Sendable` without proof. - Propagate cancellation through loops, AsyncSequence production, continuations, and I/O adapters. - Resume checked continuations exactly once on every path; retain cancellation handles for callback APIs. - Do not block cooperative executors with synchronous I/O or locks held across suspension. - Preserve actor isolation in public protocols and closures. Use `@MainActor` only for UI/main-thread state, not as a general race workaround. - Define ordering, buffering, backpressure, termination, and cleanup for AsyncStream/AsyncSequence adapters. - Treat task-local values and priorities as contextual hints, not durable business state. ## Review sequence 1. Map task creation to owners and termination conditions. 2. Trace actor isolation and `Sendable` crossings. 3. Trace cancellation from caller to resources and continuations. 4. Identify blocking work, unbounded buffers, reentrancy assumptions, and priority inversions. 5. Add deterministic lifecycle tests using clocks, continuations, or event-driven coordination. 6. Run strict-concurrency compilation and stress the affected state transitions. ```bash swift build swift test ```