Phase 2: Fix data race in GetBoardsWithCards

Add mutex synchronization for writes to board slice elements
(Cards and Lists fields) from concurrent goroutines.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/internal/api/trello.go b/internal/api/trello.go
index a19bbea..67ffad0 100644
--- a/internal/api/trello.go
+++ b/internal/api/trello.go
@@ -169,6 +169,7 @@ func (c *TrelloClient) GetBoardsWithCards(ctx context.Context) ([]models.Board,
 	}
 
 	var wg sync.WaitGroup
+	var mu sync.Mutex // Protects writes to boards slice elements
 	sem := make(chan struct{}, 5) // Limit to 5 concurrent requests
 
 	for i := range boards {
@@ -186,14 +187,18 @@ func (c *TrelloClient) GetBoardsWithCards(ctx context.Context) ([]models.Board,
 				for j := range cards {
 					cards[j].BoardName = boards[i].Name
 				}
+				mu.Lock()
 				boards[i].Cards = cards
+				mu.Unlock()
 			}
 
 			lists, err := c.getLists(ctx, boards[i].ID)
 			if err != nil {
 				log.Printf("Error fetching lists for board %s: %v", boards[i].Name, err)
 			} else {
+				mu.Lock()
 				boards[i].Lists = lists
+				mu.Unlock()
 			}
 		}(i)
 	}