When would you use ActionResult, typed results, or explicit result types in ASP.NET Core APIs?

In production I standardize success DTOs and ProblemDetails extensions, then verify generated OpenAPI against actual responses. Response typing does not replace authorization, validation, or exception mapping; it documents and constrains what the endpoint chooses to return. I test every meaningful branch, including conflict, forbidden, not found, and unexpected failure, and ensure no path silently returns 200 with an error payload. When framework conventions infer metadata, I still inspect the generated contract during upgrades. The preferred result style should reduce ambiguity across the service rather than become a syntax contest between endpoint models.