Error Handling¶

The presentation error pipeline converts errors from any source (domain exceptions,
application failures, infrastructure problems) into a consistent, renderable form.
Three components compose to form the pipeline:

ErrorPresenter adapts errors into view models — it understands framework
Error objects, Result.Err values, plain exceptions, and aggregate errors.
ErrorStatusCodeMapper assigns HTTP-like status codes so clients can
distinguish validation errors (400) from rule violations (409).
ErrorViewModel carries the structured output — a list of messages with
title, detail, field, code, and status fields.

Error Presenter¶

ErrorPresenter converts errors into ErrorViewModel instances.

It handles framework Error objects, Result.Err values, plain exceptions, and unknown types. Aggregate errors like CombinedErrors and FieldErrors are recursively decomposed into individual messages.

Error Status Code Mapper¶

ErrorStatusCodeMapper assigns HTTP-like status codes:
- Validation errors → 400
- Rule violations → 409
- Aggregate/field errors → 422
- Unknown → 500

Error View Model¶

ErrorViewModel holds a list of ErrorMessageModel entries. Each message carries:
- title — Human-readable summary
- detail — Optional longer explanation
- field — Optional field reference (e.g. "username")
- code — Optional machine-readable error code
- status_code — Optional HTTP-like status code

When to use¶

Wire ErrorPresenter, ErrorStatusCodeMapper, and ErrorViewModel into a PresentationAdapter. Pass an ErrorPresenter to catch both Result.Err and raised exceptions. Use ErrorStatusCodeMapper to attach HTTP codes before rendering.

Presenter Port¶

PresenterPort[ResponseType] is an orthogonal rendering contract. Extends InboundPort. Has present(response) for success and present_error(error) for failures. An adapter may call both a Pipeline for processing and a PresenterPort for rendering.