# BACKBEAT Integration Guide for CHORUS 2.0.0 Projects

This guide explains how to integrate BACKBEAT contract validation into your CHORUS 2.0.0 project for guaranteed compatibility with the distributed orchestration system.

## Overview

BACKBEAT provides three core interfaces for coordinated distributed execution:

- **INT-A (BeatFrame)**: Rhythm coordination from Pulse service to all agents
- **INT-B (StatusClaim)**: Agent status reporting to Reverb service  
- **INT-C (BarReport)**: Periodic summary reports from Reverb to all services

All messages must conform to the published JSON schemas to ensure reliable operation across the CHORUS ecosystem.

## Quick Start

### 1. Add Contract Validation to Your CI Pipeline

#### GitHub Actions
```yaml
name: BACKBEAT Contract Validation

on: [push, pull_request]

jobs:
  validate-backbeat:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v4
    
    - name: Checkout BACKBEAT contracts
      uses: actions/checkout@v4
      with:
        repository: 'chorus-services/backbeat'
        path: 'backbeat-contracts'
        
    - name: Set up Go
      uses: actions/setup-go@v4
      with:
        go-version: '1.22'
        
    - name: Validate BACKBEAT messages
      run: |
        cd backbeat-contracts/contracts/tests/integration
        make build
        ./backbeat-validate \
          --schemas ../../schemas \
          --dir ../../../your-messages-directory \
          --exit-code
```

#### GitLab CI
```yaml
validate-backbeat:
  stage: test
  image: golang:1.22
  before_script:
    - git clone https://github.com/chorus-services/backbeat.git /tmp/backbeat
    - cd /tmp/backbeat/contracts/tests/integration && make build
  script:
    - /tmp/backbeat/contracts/tests/integration/backbeat-validate 
        --schemas /tmp/backbeat/contracts/schemas 
        --dir $CI_PROJECT_DIR/messages 
        --exit-code
```

### 2. Project Makefile Integration

Add to your project's `Makefile`:

```makefile
# BACKBEAT contract validation
BACKBEAT_REPO = https://github.com/chorus-services/backbeat.git
BACKBEAT_DIR = .backbeat-contracts

$(BACKBEAT_DIR):
	git clone $(BACKBEAT_REPO) $(BACKBEAT_DIR)

validate-backbeat: $(BACKBEAT_DIR)
	cd $(BACKBEAT_DIR)/contracts/tests/integration && make build
	$(BACKBEAT_DIR)/contracts/tests/integration/backbeat-validate \
		--schemas $(BACKBEAT_DIR)/contracts/schemas \
		--dir messages \
		--exit-code

.PHONY: validate-backbeat
```

## Message Implementation

### Implementing BeatFrame Consumer (INT-A)

Your service should subscribe to beat frames from the Pulse service and respond appropriately:

```go
// Example Go implementation
type BeatFrameHandler struct {
    currentBeat int64
    phase       string
}

func (h *BeatFrameHandler) HandleBeatFrame(frame BeatFrame) {
    // Validate the beat frame
    if err := validateBeatFrame(frame); err != nil {
        log.Errorf("Invalid beat frame: %v", err)
        return
    }
    
    // Update internal state
    h.currentBeat = frame.BeatIndex
    h.phase = frame.Phase
    
    // Execute phase-appropriate actions
    switch frame.Phase {
    case "plan":
        h.planPhase(frame)
    case "execute":
        h.executePhase(frame)
    case "review":
        h.reviewPhase(frame)
    }
}

func validateBeatFrame(frame BeatFrame) error {
    if frame.Type != "backbeat.beatframe.v1" {
        return fmt.Errorf("invalid message type: %s", frame.Type)
    }
    if frame.TempoBPM < 0.1 || frame.TempoBPM > 1000 {
        return fmt.Errorf("invalid tempo: %f", frame.TempoBPM)
    }
    // Add more validation as needed
    return nil
}
```

### Implementing StatusClaim Publisher (INT-B)

Your agents should publish status claims to the Reverb service:

```go
func (agent *Agent) PublishStatusClaim(beatIndex int64, state string) error {
    claim := StatusClaim{
        Type:      "backbeat.statusclaim.v1",
        AgentID:   agent.ID,
        BeatIndex: beatIndex,
        State:     state,
        HLC:       agent.generateHLC(),
        Progress:  agent.calculateProgress(),
        Notes:     agent.getCurrentStatus(),
    }
    
    // Validate before sending
    if err := validateStatusClaim(claim); err != nil {
        return fmt.Errorf("invalid status claim: %w", err)
    }
    
    return agent.publisher.Publish("backbeat.statusclaims", claim)
}

func validateStatusClaim(claim StatusClaim) error {
    validStates := []string{"idle", "planning", "executing", "reviewing", "completed", "failed", "blocked", "helping"}
    for _, valid := range validStates {
        if claim.State == valid {
            return nil
        }
    }
    return fmt.Errorf("invalid state: %s", claim.State)
}
```

### Implementing BarReport Consumer (INT-C)

Services should consume bar reports for cluster health awareness:

```go
func (service *Service) HandleBarReport(report BarReport) {
    // Validate the bar report
    if err := validateBarReport(report); err != nil {
        log.Errorf("Invalid bar report: %v", err)
        return
    }
    
    // Update cluster health metrics
    service.updateClusterHealth(report)
    
    // React to issues
    if len(report.Issues) > 0 {
        service.handleClusterIssues(report.Issues)
    }
    
    // Store performance metrics
    service.storePerformanceMetrics(report.Performance)
}

func (service *Service) updateClusterHealth(report BarReport) {
    service.clusterMetrics.AgentsReporting = report.AgentsReporting
    service.clusterMetrics.OnTimeRate = float64(report.OnTimeReviews) / float64(report.AgentsReporting)
    service.clusterMetrics.TempoDrift = report.TempoDriftMS
    service.clusterMetrics.SecretRotationsOK = report.SecretRotationsOK
}
```

## Message Format Requirements

### Common Patterns

All BACKBEAT messages share these patterns:

1. **Type Field**: Must exactly match the schema constant
2. **HLC Timestamps**: Format `XXXX:XXXX:XXXX` (hex digits)
3. **Beat Indices**: Monotonically increasing integers ≥ 0
4. **Window IDs**: 32-character hexadecimal strings
5. **Agent IDs**: Pattern `service:instance` or `agent:identifier`

### Validation Best Practices

1. **Always validate messages before processing**
2. **Use schema validation in tests**
3. **Handle validation errors gracefully**
4. **Log validation failures for debugging**

Example validation function:

```go
func ValidateMessage(messageBytes []byte, expectedType string) error {
    // Parse and check type
    var msg map[string]interface{}
    if err := json.Unmarshal(messageBytes, &msg); err != nil {
        return fmt.Errorf("invalid JSON: %w", err)
    }
    
    msgType, ok := msg["type"].(string)
    if !ok || msgType != expectedType {
        return fmt.Errorf("expected type %s, got %s", expectedType, msgType)
    }
    
    // Use schema validation
    return validateWithSchema(messageBytes, expectedType)
}
```

## Tempo and Timing Considerations

### Understanding Tempo

- **Default Tempo**: 1 BPM (60-second beats)
- **Minimum Tempo**: 1 BPM (60-second beats for batch or recovery windows)
- **Maximum Tempo**: 24 BPM (~2.5-second beats for high-frequency workloads)

### Phase Timing

Each beat consists of three phases with equal time allocation:

```
Beat Duration = 60 / TempoBPM seconds
Phase Duration = Beat Duration / 3

Plan Phase:    [0, Beat Duration / 3)
Execute Phase: [Beat Duration / 3, 2 * Beat Duration / 3)  
Review Phase:  [2 * Beat Duration / 3, Beat Duration)
```

### Implementation Guidelines

1. **Respect Deadlines**: Always complete phase work before `deadline_at`
2. **Handle Tempo Changes**: Pulse may adjust tempo based on cluster performance
3. **Plan for Latency**: Factor in network and processing delays
4. **Implement Backpressure**: Report when unable to keep up with tempo

## Error Handling

### Schema Validation Failures

```go
func HandleInvalidMessage(err error, messageBytes []byte) {
    log.Errorf("Schema validation failed: %v", err)
    log.Debugf("Invalid message: %s", string(messageBytes))
    
    // Send to dead letter queue or error handler
    errorHandler.HandleInvalidMessage(messageBytes, err)
    
    // Update metrics
    metrics.InvalidMessageCounter.Inc()
}
```

### Network and Timing Issues

```go
func (agent *Agent) HandleMissedBeat(expectedBeat int64) {
    // Report missed beat
    claim := StatusClaim{
        Type:      "backbeat.statusclaim.v1",
        AgentID:   agent.ID,
        BeatIndex: expectedBeat,
        State:     "blocked",
        Notes:     "missed beat due to network issues",
        HLC:       agent.generateHLC(),
    }
    
    // Try to catch up
    agent.attemptResynchronization()
}
```

## Testing Your Integration

### Unit Tests

```go
func TestBeatFrameValidation(t *testing.T) {
    validFrame := BeatFrame{
        Type:       "backbeat.beatframe.v1",
        ClusterID:  "test",
        BeatIndex:  100,
        Downbeat:   false,
        Phase:      "execute",
        HLC:        "7ffd:0001:abcd",
        DeadlineAt: time.Now().Add(30 * time.Second),
        TempoBPM:   2.0,
        WindowID:   "7e9b0e6c4c9a4e59b7f2d9a3c1b2e4d5",
    }
    
    err := validateBeatFrame(validFrame)
    assert.NoError(t, err)
}
```

### Integration Tests

Use the BACKBEAT validation tools:

```bash
# Test your message files
backbeat-validate --schemas /path/to/backbeat/schemas --dir messages/

# Test individual messages  
echo '{"type":"backbeat.beatframe.v1",...}' | backbeat-validate --schemas /path/to/backbeat/schemas --message -
```

### Load Testing

Consider tempo and message volume in your load tests:

```go
func TestHighTempoHandling(t *testing.T) {
    // Simulate 10 BPM (6-second beats)
    tempo := 10.0
    beatInterval := time.Duration(60/tempo) * time.Second
    
    for i := 0; i < 100; i++ {
        frame := generateBeatFrame(i, tempo)
        handler.HandleBeatFrame(frame)
        time.Sleep(beatInterval)
    }
    
    // Verify no beats were dropped
    assert.Equal(t, 100, handler.processedBeats)
}
```

## Production Deployment

### Monitoring

Monitor these key metrics:

1. **Message Validation Rate**: Percentage of valid messages received
2. **Beat Processing Latency**: Time to process each beat phase
3. **Missed Beat Count**: Number of beats that couldn't be processed on time
4. **Schema Version Compatibility**: Ensure all services use compatible versions

### Alerting

Set up alerts for:

- Schema validation failures > 1%
- Beat processing latency > 90% of phase duration
- Missed beats > 5% in any 10-minute window
- HLC timestamp drift > 5 seconds

### Gradual Rollout

1. **Validate in CI**: Ensure all messages pass schema validation
2. **Deploy to dev**: Test with low tempo (0.5 BPM)
3. **Staging validation**: Use production-like tempo and load
4. **Canary deployment**: Roll out to small percentage of production traffic
5. **Full production**: Monitor closely and be ready to rollback

## Troubleshooting

### Common Issues

1. **Wrong Message Type**: Ensure `type` field exactly matches schema
2. **HLC Format**: Must be `XXXX:XXXX:XXXX` format with hex digits
3. **Window ID Length**: Must be exactly 32 hex characters
4. **Enum Values**: States, phases, severities must match schema exactly
5. **Numeric Ranges**: Check min/max constraints (tempo, beat_index, etc.)

### Debug Tools

```bash
# Validate specific message
backbeat-validate --schemas ./schemas --message '{"type":"backbeat.beatframe.v1",...}'

# Get detailed validation errors
backbeat-validate --schemas ./schemas --file message.json --json

# Validate entire directory with detailed output
backbeat-validate --schemas ./schemas --dir messages/ --json > validation-report.json
```

## Schema Evolution

See [schema-evolution.md](schema-evolution.md) for details on:

- Semantic versioning for schemas
- Backward compatibility requirements
- Migration strategies for schema updates
- Version compatibility matrix

## Performance Guidelines

See [tempo-guide.md](tempo-guide.md) for details on:

- Choosing appropriate tempo for your workload
- Optimizing beat processing performance
- Handling tempo changes gracefully
- Resource utilization best practices

## Support

- **Documentation**: This contracts package contains the authoritative reference
- **Examples**: See `contracts/tests/examples/` for valid/invalid message samples
- **Issues**: Report integration problems to the BACKBEAT team
- **Updates**: Monitor the contracts repository for schema updates