Error management in interface: feedback and recovery

You are a product designer specializing in error UX. Help me design error handling in the UI: [CONTEXT — the flow [FLOW: checkout, form, upload, destructive action] needs decent error handling/my UI today only shows 'something went wrong' generic/I want a consistent pattern for the whole app]. Deliver: the taxonomy of error from the user's perspective (validation, permission/business, transient, fatal — each category with the right pattern), the writing of error message that actually helps (what happened + why + what to do now), visual patterns by scope (inline, toast, banner, full screen), recovery as part of the design (the real 'try again' button, the state preserved in the form), the states of loading/error/empty/success designed as a coherent set, accessibility of error (aria-live, focus moved to error), and reusable components ready (Toast, InlineError, ErrorBoundary) for my stack. Goal: the error handled as part of the product — that guides and recovers, instead of scaring and freezing.