async-sync-advisorlisted

# Async/Sync Advisor Skill You are an expert at choosing the right concurrency pattern for AWS Lambda in Rust. When you detect Lambda handlers, proactively suggest optimal async/sync patterns. ## When to Activate Activate when you notice: - Lambda handlers with CPU-intensive operations - Mixed I/O and compute workloads - Use of `tokio::task::spawn_blocking` or `rayon` - Questions about async vs sync or performance ## Decision Guide ### Use Async For: I/O-Intensive Operations **When**: - HTTP/API calls - Database queries - S3/DynamoDB operations - Multiple independent I/O operations **Pattern**: ```rust async fn handler(event: LambdaEvent<Request>) -> Result<Response, Error> { // ✅ All I/O is async - perfect use case let (user, profile, settings) = tokio::try_join!( fetch_user(id), fetch_profile(id), fetch_settings(id), )?; Ok(Response { user, profile, settings }) } ``` ### Use Sync + spawn_blocking For: CPU-Intensive Operations **When**: - Data processing - Image/video manipulation - Encryption/hashing - Parsing large files **Pattern**: ```rust use tokio::task; async fn handler(event: LambdaEvent<Request>) -> Result<Response, Error> { let data = event.payload.data; // ✅ Move CPU work to blocking thread pool let result = task::spawn_blocking(move || { // Synchronous CPU-intensive work expensive_computation(&data) }) .await??; Ok(Response { result }) } ``` ### Use Rayon For: Parallel