Fix GUI background image generation race conditions

- Add file.Sync() after image download to ensure data is flushed to disk
- Add double-checking in UI updates to prevent wrong card updates
- Fix background job completion to reload files when user navigates back
- Add file size validation in image display widget
- Improve error messages for image loading failures

This fixes two issues:
1. 'png: invalid format: not enough pixel data' error when navigating during generation
2. Images not updating when navigating back to a card after background generation completes

1 files changed, 16 insertions, 3 deletions

diff --git a/internal/gui/widgets.go b/internal/gui/widgets.go
index 6ad428c..df74027 100644
--- a/internal/gui/widgets.go
+++ b/internal/gui/widgets.go
@@ -73,7 +73,20 @@ func (d *ImageDisplay) SetImage(imagePath string) {
 	}
 	defer file.Close()
 
-	img, _, err := image.Decode(file)
+	// Get file info to ensure it's fully written
+	stat, err := file.Stat()
+	if err != nil {
+		d.imageLabel.SetText(fmt.Sprintf("Error getting file info: %v", err))
+		return
+	}
+
+	// If file size is 0, it might still be writing
+	if stat.Size() == 0 {
+		d.imageLabel.SetText("Image file is empty")
+		return
+	}
+
+	img, format, err := image.Decode(file)
 	if err != nil {
 		d.imageLabel.SetText(fmt.Sprintf("Error decoding image: %v", err))
 		return
@@ -83,8 +96,8 @@ func (d *ImageDisplay) SetImage(imagePath string) {
 	d.imageCanvas.Image = img
 	d.imageCanvas.Refresh()
 
-	// Update label
-	d.imageLabel.SetText(filepath.Base(imagePath))
+	// Update label with format info
+	d.imageLabel.SetText(fmt.Sprintf("%s (%s)", filepath.Base(imagePath), format))
 }
 
 // SetImages sets multiple images but only displays the first one