Implement request error handling

Every requests is just doing its thing, while we do not check for any error. This is a bit intentional because we do not know the error yet.

When we collect some common errors, we should add some error handlers.

The issue does not identify any files, request entry points, tests, or specific errors. First inspect the request implementations and existing tests, then establish which common errors are in scope; done means those agreed errors are handled and the behavior is covered by tests.

Written by the indexing model from the issue text.