# Cron Trigger System - Integration Complete

## Summary

The cron trigger system has been fully integrated into wg, enabling time-based task scheduling for operational workloads like nightly cleanups, health checks, and recurring maintenance tasks.

## Components Implemented

### 1. Core Cron Module (`src/cron.rs`) ✅
- **Cron expression parsing**: Supports both 5-field and 6-field cron formats
- **Schedule calculation**: Calculates next fire times based on cron expressions  
- **Due checking**: Determines when cron tasks are ready to trigger
- **Comprehensive test coverage**: Unit tests for all core functionality

### 2. Task Data Model (`src/graph.rs`) ✅
- **cron_schedule**: Optional string field for cron expressions
- **cron_enabled**: Boolean flag to enable/disable cron functionality
- **last_cron_fire**: Timestamp of last trigger (ISO 8601 format)
- **next_cron_fire**: Calculated next trigger time
- **Serialization support**: Full JSON serialization/deserialization

### 3. CLI Integration (`src/commands/add.rs`) ✅
- **--cron flag**: Enables creating cron tasks via `wg add --cron "expression"`
- **Expression validation**: Validates cron expressions at task creation time
- **Next fire calculation**: Pre-calculates initial next fire time
- **Error handling**: Clear error messages for invalid cron expressions

### 4. Coordinator Integration (`src/commands/service/coordinator.rs`) ✅
- **Cron trigger checking**: Integrated into coordinator tick loop (Phase 2.10)
- **Task instance creation**: Auto-creates task instances from cron templates
- **Timing updates**: Updates last/next fire times on template tasks
- **Conflict handling**: Handles overlapping executions gracefully

### 5. Test Coverage ✅
- **Unit tests**: Core cron module functionality
- **Integration tests**: End-to-end cron workflow testing
- **Serialization tests**: Verify cron fields persist correctly
- **Manual verification**: Script for testing complete workflow

## Usage Examples

### Create Cron Tasks
```bash
# Nightly cleanup at 2 AM
wg add "nightly cleanup" --cron "0 2 * * *" -d "Clean up old logs and temp files"

# Health check every 5 minutes
wg add "health check" --cron "*/5 * * * *" -d "Check service health"

# Weekly backup on Sundays at midnight
wg add "weekly backup" --cron "0 0 * * 0" -d "Backup important data"
```

### Start Coordinator
```bash
wg service start --max-agents 4
```
The coordinator will automatically check for due cron triggers and create task instances.

## Architecture

### Cron Template vs Instance Tasks
- **Template tasks**: Cron-enabled tasks that serve as blueprints
- **Instance tasks**: Auto-created copies when cron triggers fire
- **Unique IDs**: Instances get timestamp-suffixed IDs (e.g., `cleanup-2026-04-12-02-00-00`)
- **State isolation**: Instances start fresh with Open status, empty logs/artifacts

### Integration Points
- **Phase 2.10**: Cron checking runs in coordinator maintenance phase
- **File locking**: Safe concurrent access to graph during cron processing
- **Error handling**: Non-blocking - invalid cron expressions don't stop coordinator

## Validation Criteria Met ✅

- [x] All cron-related tests pass
- [x] No regressions in existing functionality  
- [x] End-to-end workflow validated
- [x] Documentation updated
- [x] Implementation ready for production use

## Files Modified/Added

### Core Implementation
- `src/cron.rs` - Core cron functionality
- `src/commands/add.rs` - CLI integration
- `src/commands/service/coordinator.rs` - Coordinator integration
- `src/graph.rs` - Task data model (cron fields already present)

### Tests
- `tests/test_cron_integration.rs` - Comprehensive integration tests
- `tests/test_cron_serialization.rs` - Serialization tests

### Documentation & Verification
- `cron_triggers_design.md` - Design document
- `CRON_INTEGRATION_COMPLETE.md` - This summary
- `verify_cron_integration.sh` - Manual verification script

## Production Readiness

The cron trigger system is complete and production-ready:

✅ **Robust error handling**: Invalid expressions don't crash the coordinator  
✅ **Concurrent safety**: Uses existing graph locking mechanisms  
✅ **Backwards compatibility**: No breaking changes to existing functionality  
✅ **Comprehensive testing**: Unit tests, integration tests, manual verification  
✅ **Clear documentation**: Usage examples and architecture explanation

The system enables wg to handle both event-driven coordination and time-driven operational tasks, providing a complete task orchestration platform.