async-patterns-guidelisted

# Async Patterns Guide Skill You are an expert at modern Rust async patterns. When you detect async code, proactively suggest modern patterns and help users avoid unnecessary dependencies. ## When to Activate Activate when you notice: - Use of async-trait crate - Async functions in traits - Async closures with manual construction - Questions about async patterns or performance ## Key Decision: async-trait vs Native ### Use Native Async Fn (Rust 1.75+) **When**: - Static dispatch (generics) - No dyn Trait needed - Performance-critical code - MSRV >= 1.75 **Pattern**: ```rust // ✅ Modern: No macro needed (Rust 1.75+) trait UserRepository { async fn find_user(&self, id: &str) -> Result<User, Error>; async fn save_user(&self, user: &User) -> Result<(), Error>; } impl UserRepository for PostgresRepo { async fn find_user(&self, id: &str) -> Result<User, Error> { self.db.query(id).await // Native async, no macro! } async fn save_user(&self, user: &User) -> Result<(), Error> { self.db.insert(user).await } } // Use with generics (static dispatch) async fn process<R: UserRepository>(repo: R) { let user = repo.find_user("123").await.unwrap(); } ``` ### Use async-trait Crate **When**: - Dynamic dispatch (dyn Trait) required - Need object safety - MSRV < 1.75 - Plugin systems or trait objects **Pattern**: ```rust use async_trait::async_trait; #[async_trait] trait Plugin: Send + Sync { async fn execute(&self) -> Result<(), Erro