<skill_overview> Design predictable and ergonomic error handling in Rust

Designing error types Propagating errors with Result Mapping errors at API boundaries Choosing between panic and Result

The Rust Book - Error Handling

</skill_overview> <panic_vs_result> <use_panic_when> Unrecoverable, invariant-breaking failures Bug in the program (logic error) </use_panic_when> <use_result_when> Expected errors (not found, validation) I/O or external dependency failures </use_result_when> </panic_vs_result> <error_types>

Define a dedicated error enum for a module or service Implement Display and Error for custom errors Use From to convert lower-level errors

enum ServiceError { NotFound, InvalidInput, Io(std::io::Error) }

</error_types>

Use ? to propagate errors Add context with map_err or custom variants Preserve original error for debugging

<boundary_mapping>

Map internal errors to public error codes/messages Do not leak sensitive details to clients

</boundary_mapping> <anti_patterns> Avoid unwrap/expect for normal flow Avoid plain String errors without structure Do not panic on validation failures </anti_patterns>