# Story 1.4: Error Handling and Error Bus

## Metadata
- **Story ID**: 1.4
- **Title**: Error Handling and Error Bus
- **Epic**: 1 - Core Kernel & Infrastructure
- **Status**: Completed
- **Priority**: High
- **Estimated Time**: 4-5 hours
- **Dependencies**: 1.1, 1.3

## Goal
Implement centralized error handling with an error bus that captures, logs, and optionally reports all application errors.

## Description
This story creates a complete error handling system with an error bus that captures all errors, logs them with context, and provides a foundation for future error reporting integrations (like Sentry).

## Deliverables

### 1. Error Bus Interface (`pkg/errorbus/errorbus.go`)
- `ErrorPublisher` interface with `Publish(err error)` method
- Error context support
- Error categorization

### 2. Channel-Based Error Bus (`internal/errorbus/channel_bus.go`)
- Buffered channel for error publishing
- Background goroutine consumes errors
- Logs all errors with context (request ID, user ID, etc.)
- Error aggregation
- Optional: Sentry integration placeholder (Epic 6)

### 3. Panic Recovery Middleware
- Recovers from panics in HTTP handlers
- Publishes panics to error bus
- Returns appropriate HTTP error responses (500)
- Preserves error context

### 4. Integration
- Integration with DI container
- Integration with HTTP middleware stack
- Integration with logger

## Implementation Steps

1. **Create Error Bus Interface**
   - Create `pkg/errorbus/errorbus.go`
   - Define ErrorPublisher interface

2. **Implement Channel-Based Error Bus**
   - Create `internal/errorbus/channel_bus.go`
   - Implement buffered channel
   - Implement background consumer
   - Add error logging

3. **Create Panic Recovery Middleware**
   - Create middleware for Gin
   - Recover from panics
   - Publish to error bus
   - Return error responses

4. **Integrate with DI**
   - Create provider function
   - Register in container

5. **Integrate with HTTP Server**
   - Add panic recovery middleware
   - Test error handling

## Acceptance Criteria
- [x] Errors are captured and logged via error bus
- [x] Panics are recovered and logged
- [x] HTTP handlers return proper error responses
- [x] Error bus is injectable via DI
- [x] Error context (request ID, user ID) is preserved
- [x] Background error consumer works correctly
- [x] Error bus doesn't block request handling

## Related ADRs
- [ADR-0015: Error Bus Implementation](../../adr/0015-error-bus-implementation.md)
- [ADR-0026: Error Reporting Service](../../adr/0026-error-reporting-service.md)

## Implementation Notes
- Use buffered channels to prevent blocking
- Background goroutine should handle errors asynchronously
- Preserve error context (stack traces, request IDs)
- Consider error rate limiting in future
- Placeholder for Sentry integration in Epic 6

## Testing
```bash
# Test error bus
go test ./internal/errorbus/...

# Test panic recovery
# Trigger panic in handler and verify recovery
```

## Files to Create/Modify
- `pkg/errorbus/errorbus.go` - Error bus interface
- `internal/errorbus/channel_bus.go` - Error bus implementation
- `internal/server/middleware.go` - Panic recovery middleware
- `internal/di/providers.go` - Add error bus provider