Implement opal-task Phase 5: Recurrence Implementation

- Complete SpawnNextInstance() for creating recurring task instances
- Implement automatic next instance spawning on task completion
- Add support for 'until' date to expire recurrences
- Copy tags from template to new instances
- Add comprehensive recurrence tests (6 tests, all passing)
- Test pattern parsing, formatting, next due calculation
- Test end-to-end recurring task workflow
- Test expiration with until dates

opal-task/internal/engine/recurrence.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"strconv"
 	"time"
+
+	"github.com/google/uuid"
 )
 
 // ParseRecurrencePattern converts "1w", "2d", "1m" to time.Duration
@@ -58,12 +60,67 @@ func CalculateNextDue(currentDue time.Time, recurrence time.Duration) time.Time
 }
 
 // SpawnNextInstance creates a new task instance from completed recurring task
-// This will be implemented after we have the CRUD operations
 func SpawnNextInstance(completedInstance *Task) error {
 	if completedInstance.ParentUUID == nil {
 		return fmt.Errorf("task is not a recurring instance")
 	}
 
-	// TODO: Implement after GetTask is available
-	return fmt.Errorf("not implemented yet")
+	// Load template
+	template, err := GetTask(*completedInstance.ParentUUID)
+	if err != nil {
+		return fmt.Errorf("failed to load template: %w", err)
+	}
+
+	if template.RecurrenceDuration == nil {
+		return fmt.Errorf("template has no recurrence duration")
+	}
+
+	// Calculate next due date
+	var nextDue *time.Time
+	if completedInstance.Due != nil {
+		next := CalculateNextDue(*completedInstance.Due, *template.RecurrenceDuration)
+		nextDue = &next
+	}
+
+	// Check if we're past 'until' date
+	if template.Until != nil && nextDue != nil && nextDue.After(*template.Until) {
+		// Don't spawn, recurrence has expired
+		return nil
+	}
+
+	// Create new instance
+	now := time.Now()
+	newInstance := &Task{
+		UUID:        uuid.New(),
+		Status:      StatusPending,
+		Description: template.Description,
+		Project:     template.Project,
+		Priority:    template.Priority,
+		Created:     now,
+		Modified:    now,
+		Due:         nextDue,
+		Scheduled:   template.Scheduled,
+		Wait:        template.Wait,
+		Until:       template.Until,
+		ParentUUID:  &template.UUID,
+		Tags:        []string{},
+	}
+
+	if err := newInstance.Save(); err != nil {
+		return fmt.Errorf("failed to save new instance: %w", err)
+	}
+
+	// Copy tags from template
+	templateTags, err := template.GetTags()
+	if err != nil {
+		return fmt.Errorf("failed to get template tags: %w", err)
+	}
+
+	for _, tag := range templateTags {
+		if err := newInstance.AddTag(tag); err != nil {
+			return fmt.Errorf("failed to add tag: %w", err)
+		}
+	}
+
+	return nil
 }