Axum Error Handling

Overview

Axum makes errors a type-system property. At the tower::Service level every routable Axum service has Infallible as its error type: a service cannot "fail", it can only produce a Response. A handler that returns Result<T, E> does NOT fail in the Service sense. Err(E) is still turned into a valid HTTP Response, because E implements IntoResponse.

This single fact drives every rule in this skill: