Rust Async and Concurrency

Use this when work crosses task or thread boundaries, or when runtime and shutdown behaviour shape the design more than syntax does.

Working stance

• Decide who owns a task and how it stops before wiring the happy path.
• Prefer message passing over shared mutable state when ownership is unclear.
• Never hold a lock guard across an .await.
• Keep blocking and CPU-heavy work out of async executors.
• Treat Send and Sync errors as design feedback, not compiler trivia.
• Cancellation needs an explicit contract, not just dropped futures.

Decision surface