v0.3.0

[0.3.0] - 2025-12-26

Added

• Error::with_cause_message() method for fluent builder-style cause attachment
• Domain error mapping documentation in API.md (thiserror pattern with From trait)
• API.md: Complete API reference extracted from README (364 lines)
• ERROR_CODES.md: Complete error codes reference with all 18 codes (167 lines)
• ARCHITECTURE.md: Visual architecture guide with 4 mermaid diagrams (272 lines)
• Four new examples:
  • domain_errors.rs - thiserror → error-envelope mapping via From trait
  • validation.rs - Field-level validation with structured error details
  • rate_limiting.rs - Rate limiting with retry_after and time windows
  • tracing.rs - Trace ID propagation through middleware

Changed

• README restructured as landing page (337→235 lines, 30% reduction)
• Hero example now compile-clean with struct definitions and proper HashMap types
• Hero example demonstrates validation errors with structured field details
• Quick Start reduced to minimal rate limiting example (demonstrates retry_after)
• Table of Contents now has clickable links to sections and external docs
• "Why error-envelope" section reframed around formal error contracts
• Overview section reordered to lead with anyhow and Axum integration
• anyhow integration description clarified: "at the HTTP boundary"
• Design Principles section condensed with link to ARCHITECTURE.md
• Stack architecture explicitly documented: anyhow → error-envelope → Axum
• Examples section reorganized to list all five examples with descriptions