| name | swift-concurrency-safety |
| description | Design and review Swift 6 concurrency boundaries using structured tasks, actors, Sendable values, cancellation, and compiler-backed data-race safety. |
Swift Concurrency Safety
Use this skill for async features, Swift 6 migration, actor-isolation errors, Sendable warnings, task cancellation, or UI work that crosses concurrency domains.
Workflow
- Record the target's Swift language mode and concurrency-checking settings.
- Map mutable state and its owner before adding tasks or annotations.
- Keep UI state on the main actor. Move long-running work behind async service boundaries instead of blocking the actor.
- Prefer structured child tasks. Use detached or unstructured tasks only when lifetime and cancellation are explicitly owned.
- Pass immutable Sendable values across isolation boundaries. Do not hide warnings with unchecked conformance until invariants are documented and tested.
- Propagate cancellation and define what partial work is rolled back or retained.
- Compile with the project's strictest supported concurrency checks and test ordering, cancellation, failure, and reentrancy.
Review failures
- Actor annotations added only to silence diagnostics.
Task {} used as an ownership escape hatch.- UI-observable models mutated off the main actor.
- Mutable reference types crossing actors without an isolation plan.
- Continuations that can resume twice or never resume.
- Async APIs with no cancellation or timeout behavior.
Read references/migration.md before changing language mode or performing a broad migration.
