Rust

Writes, debugs, and optimizes Rust code, crates, and Cargo builds: ownership, lifetimes, traits, async, unsafe, and FFI. Use when the borrow checker rejects code, when rustc reports value moved, cannot borrow as mutable, does not live long enough, missing lifetime specifier, trait bound not satisfied, or not dyn compatible; when a future cannot be sent between threads, a Mutex guard crosses an await, a task blocks the async runtime, or select! loses data; when code deadlocks, panics on unwrap, or hits BorrowMutError; when cargo builds are slow, features unify unexpectedly, two versions of one crate collide, or the build fails only in CI; when writing unsafe, C FFI, proc macros, serde derives, no_std firmware, or wasm; when cross-compiling to musl or another target; when profiling, benchmarking, or shrinking a Rust binary. Not for C++ or language-agnostic concurrency theory.