docs: and skills

bin/.claude/skills/ddd-model/rules/error-handling.md

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+# Error Handling in DDD
+
+This document defines error handling principles that apply across all layers and languages.
+
+## Core Principles
+
+1. **No Silent Failures** - All errors must be explicitly handled or propagated
+2. **Layer-Specific Errors** - Each layer defines its own error types
+3. **Error Transformation** - Errors are transformed at layer boundaries
+4. **Proper Logging** - Original errors logged before transformation
+5. **Result Types Over Exceptions** - Prefer Result types (where supported) over exceptions
+
+## Language-Specific Implementation
+
+- **Java**: See [languages/java/error-handling.md](../languages/java/error-handling.md)
+- **Go**: Use error returns and custom error types
+
+## Error Hierarchy
+
+```
+Domain Errors (business rule violations)
+  ↓ transformed at boundary
+Application Errors (use case failures)
+  ↓ transformed at boundary  
+Infrastructure Errors (technical failures)
+```
+
+## Logging Strategy
+
+- **ERROR**: Infrastructure failures (database down, network error)
+- **WARN**: Business rule violations (insufficient funds, invalid state)
+- **INFO**: Normal operations (order placed, account created)
+- **DEBUG**: Detailed flow information
+- **TRACE**: Original errors when transforming between layers
+
+## Exception Boundary
+
+**Infrastructure Layer** is the exception boundary:
+- Infrastructure catches external exceptions (SQL, HTTP, etc.)
+- Transforms to domain error types
+- Logs original exception at ERROR level
+- Returns domain error type
+
+**Domain and Application** layers:
+- Never throw exceptions (use Result types or errors)
+- Only work with domain/application error types
+- No try/catch blocks needed