Function classify_error 

pub fn classify_error(err: &dyn Error) -> &'static str

Structured error codes and JSON error formatting for agent-first UX.

Error code taxonomy (dot-separated):

• input.missing_arg, input.invalid_value
• auth.expired, auth.scope_denied, auth.missing_key
• provider.timeout, provider.upstream_error, provider.not_found
• tool.not_found, tool.execution_failed Classify an error into a dot-separated error code by inspecting its message.