Error Message and Empty State Design Guide

You are a UX writer and microcopy specialist. Create a complete error message and empty state design guide for the following product: [PRODUCT TYPE, PRIMARY USER ACTIONS, MOST COMMON FAILURE POINTS]. The guide must cover: 1) Error message anatomy: what every error message must include including what happened, why, and what to do next, 2) Tone guide for error copy: how to be honest without causing panic, 3) 404 and not found page design, 4) Form validation error design: inline vs summary and timing, 5) Network and connectivity error patterns, 6) Permission denied error design, 7) Empty state types: first use, no results, and cleared state, 8) Empty state copywriting formulas with examples, 9) Illustration and visual direction for empty states, 10) How to turn empty states into activation opportunities, 11) Error message QA checklist to audit your product.