fix: break sync feedback loop, respect timestamps, surface errors

- Add migration v2: source column on change_log to distinguish local
  vs sync-originated entries, preventing the echo loop where synced
  tasks get re-pushed as local changes
- PushChanges handler now skips save when server version is newer
- Client PushChanges/pushQueuedChanges collect and report marshal errors
  instead of silently dropping them
- De-duplicate getLocalChanges/getLastSyncTime into exported sync
  package functions
- Fix logConflict winner detection via pointer identity instead of
  fragile UUID+timestamp comparison
- Fix sync down to actually parse, save, and tag-sync pulled changes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

opal-task/cmd/sync.go

@@ -224,8 +224,8 @@ var syncUpCmd = &cobra.Command{
 		client := sync.NewClient(cfg.SyncURL, cfg.SyncAPIKey, cfg.SyncClientID)
 
 		// Get local changes
-		lastSync := getLastSyncTime(cfg.SyncClientID)
-		localChanges, err := getLocalChanges(lastSync)
+		lastSync := sync.GetLastSyncTime(cfg.SyncClientID)
+		localChanges, err := sync.GetLocalChanges(lastSync)
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "Error getting local changes: %v\n", err)
 			os.Exit(1)
@@ -264,7 +264,7 @@ var syncDownCmd = &cobra.Command{
 		}
 
 		client := sync.NewClient(cfg.SyncURL, cfg.SyncAPIKey, cfg.SyncClientID)
-		lastSync := getLastSyncTime(cfg.SyncClientID)
+		lastSync := sync.GetLastSyncTime(cfg.SyncClientID)
 
 		changes, err := client.PullChanges(lastSync)
 		if err != nil {
@@ -277,7 +277,55 @@ var syncDownCmd = &cobra.Command{
 			return
 		}
 
-		fmt.Printf("✓ Pulled %d changes from server\n", len(changes))
+		// Parse changes into tasks
+		tasks, err := client.ParseChanges(changes)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error parsing changes: %v\n", err)
+			os.Exit(1)
+		}
+
+		// Apply each task locally
+		var applied int
+		for _, task := range tasks {
+			if err := task.Save(); err != nil {
+				fmt.Fprintf(os.Stderr, "Warning: failed to save task %s: %v\n", task.UUID, err)
+				continue
+			}
+
+			// Mark as sync-originated to prevent feedback loop
+			_ = engine.MarkChangeLogAsSync(task.UUID.String())
+
+			// Sync tags
+			savedTask, err := engine.GetTask(task.UUID)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Warning: failed to reload task %s: %v\n", task.UUID, err)
+				continue
+			}
+
+			currentTags, _ := savedTask.GetTags()
+			currentSet := make(map[string]bool)
+			for _, tag := range currentTags {
+				currentSet[tag] = true
+			}
+			desiredSet := make(map[string]bool)
+			for _, tag := range task.Tags {
+				desiredSet[tag] = true
+			}
+			for tag := range currentSet {
+				if !desiredSet[tag] {
+					savedTask.RemoveTag(tag)
+				}
+			}
+			for tag := range desiredSet {
+				if !currentSet[tag] {
+					savedTask.AddTag(tag)
+				}
+			}
+
+			applied++
+		}
+
+		fmt.Printf("✓ Pulled %d changes, applied %d tasks from server\n", len(changes), applied)
 	},
 }
 
@@ -414,63 +462,6 @@ func init() {
 	syncCmd.PersistentFlags().BoolVarP(&quietFlag, "quiet", "q", false, "Suppress progress output")
 }
 
-// Helper functions
-
-func getLastSyncTime(clientID string) int64 {
-	db := engine.GetDB()
-	if db == nil {
-		return 0
-	}
-
-	var lastSync int64
-	err := db.QueryRow("SELECT last_sync FROM sync_state WHERE client_id = ?", clientID).Scan(&lastSync)
-	if err != nil {
-		return 0
-	}
-
-	return lastSync
-}
-
-func getLocalChanges(since int64) ([]*engine.Task, error) {
-	db := engine.GetDB()
-	if db == nil {
-		return nil, fmt.Errorf("database not initialized")
-	}
-
-	rows, err := db.Query(`
-		SELECT DISTINCT task_uuid
-		FROM change_log
-		WHERE changed_at > ?
-		ORDER BY changed_at ASC
-	`, since)
-	if err != nil {
-		return nil, err
-	}
-	defer rows.Close()
-
-	var tasks []*engine.Task
-	for rows.Next() {
-		var uuidStr string
-		if err := rows.Scan(&uuidStr); err != nil {
-			continue
-		}
-
-		taskUUID, err := uuid.Parse(uuidStr)
-		if err != nil {
-			continue
-		}
-
-		task, err := engine.GetTask(taskUUID)
-		if err != nil {
-			continue
-		}
-
-		tasks = append(tasks, task)
-	}
-
-	return tasks, nil
-}
-
 func formatTimestamp(ts int64) string {
 	t := time.Unix(ts, 0)
 	now := time.Now()