Rust Core Toolchain Conventions

Edition and Toolchain

• Target Rust 2024 edition. MSRV is set by the most-constrained transitive dependency, not the edition floor — pin it explicitly in Cargo.toml (rust-version = "...").
• Gate every change on cargo fmt --check, cargo clippy -- -D warnings, and cargo test.
• Prefer cargo nextest run for faster, isolated test execution when available.

Ownership and Borrowing

• Borrow by default, own only when necessary. Accept &str / &[T] in function signatures, not String / Vec<T>, unless the function must take ownership.
• Return owned values; let callers borrow. Avoid returning references tied to locals.
• Reach for Cow<'_, str> when a value is usually borrowed but occasionally owned.
• Use Rc/Arc only for genuine shared ownership; prefer passing references first.
• Interior mutability: Cell/RefCell for single-threaded, Mutex/RwLock (under Arc) for shared-state concurrency. Never hold a lock across an .await.