Custom error types with thiserror for domain errors

For production code, I define custom error enums using thiserror. It auto-derives Display and Error trait implementations, making errors self-documenting and composable. Each variant can wrap underlying errors (#[from]) for automatic conversion with ?. This gives you typed errors with context rather than generic strings or Box<dyn Error>. I keep one error enum per module or domain, with variants for each failure mode. The #[error("...")] attribute provides user-facing messages with interpolation. When debugging, the full chain is preserved. This pattern scales well: it's zero-cost at runtime, compiler-checked, and far more maintainable than string-based errors. I use it in every Rust library I build.