Refactor image conversion to return success status and base64 content

app/MindWork AI Studio/Agents/AgentDataSourceSelection.cs

@@ -159,7 +159,9 @@ public sealed class AgentDataSourceSelection (ILogger<AgentDataSourceSelection>
             ContentText text => text.Text,
 
             // Image prompts may be empty, e.g., when the image is too large:
-            ContentImage image => await image.AsBase64(token),
+            ContentImage image => await image.TryAsBase64(token) is (success: true, { } base64Image)
+                ? base64Image 
+                : string.Empty,
 
             // Other content types are not supported yet:
             _ => string.Empty,

app/MindWork AI Studio/Agents/AgentRetrievalContextValidation.cs

@@ -219,7 +219,9 @@ public sealed class AgentRetrievalContextValidation (ILogger<AgentRetrievalConte
                 ContentText text => text.Text,
 
                 // Image prompts may be empty, e.g., when the image is too large:
-                ContentImage image => await image.AsBase64(token),
+                ContentImage image => await image.TryAsBase64(token) is (success: true, { } base64Image)
+                    ? base64Image 
+                    : string.Empty,
 
                 // Other content types are not supported yet:
                 _ => string.Empty,

app/MindWork AI Studio/Chat/ChatThread.cs

@@ -238,7 +238,7 @@ public sealed record ChatThread
         {
             var (contentData, contentType) = block.Content switch
             {
-                ContentImage image => (await image.AsBase64(token), Tools.ERIClient.DataModel.ContentType.IMAGE),
+                ContentImage image => (await image.TryAsBase64(token) is (success: true, { } base64Image) ? base64Image : string.Empty, Tools.ERIClient.DataModel.ContentType.IMAGE),
                 ContentText text => (text.Text, Tools.ERIClient.DataModel.ContentType.TEXT),
                 
                 _ => (string.Empty, Tools.ERIClient.DataModel.ContentType.UNKNOWN),

app/MindWork AI Studio/Chat/IImageSourceExtensions.cs

@@ -12,21 +12,25 @@ public static class IImageSourceExtensions
     /// <remarks>
     /// The images are directly converted to base64 strings. The maximum
     /// size of the image is around 10 MB. If the image is larger, the method
-    /// returns an empty string.
+    /// returns an empty string.<br/>
-    /// 
+    /// <br/>
     /// As of now, this method does no sort of image processing. LLMs usually
     /// do not work with arbitrary image sizes. In the future, we might have
-    /// to resize the images before sending them to the model.
+    /// to resize the images before sending them to the model.<br/>
+    /// <br/>
+    /// Note as well that this method returns just the base64 string without
+    /// any data URI prefix (like "data:image/png;base64,"). The caller has
+    /// to take care of that if needed.
     /// </remarks>
     /// <param name="image">The image source.</param>
     /// <param name="token">The cancellation token.</param>
     /// <returns>The image content as a base64 string; might be empty.</returns>
-    public static async Task<string> AsBase64(this IImageSource image, CancellationToken token = default)
+    public static async Task<(bool success, string base64Content)> TryAsBase64(this IImageSource image, CancellationToken token = default)
     {
         switch (image.SourceType)
         {
             case ContentImageSource.BASE64:
-                return image.Source;
+                return (success: true, image.Source);
             
             case ContentImageSource.URL:
             {
@@ -39,14 +43,15 @@ public static class IImageSourceExtensions
                     if(lengthBytes > 10_000_000)
                     {
                         await MessageBus.INSTANCE.SendError(new(Icons.Material.Filled.ImageNotSupported, TB("The image at the URL is too large (>10 MB). Skipping the image.")));
-                        return string.Empty;
+                        return (success: false, string.Empty);
                     }
 
                     var bytes = await response.Content.ReadAsByteArrayAsync(token);
-                    return Convert.ToBase64String(bytes);
+                    return (success: true, Convert.ToBase64String(bytes));
                 }
 
-                return string.Empty;
+                await MessageBus.INSTANCE.SendError(new(Icons.Material.Filled.ImageNotSupported, TB("Failed to download the image from the URL. Skipping the image.")));
+                return (success: false, string.Empty);
             }
 
             case ContentImageSource.LOCAL_PATH:
@@ -57,17 +62,18 @@ public static class IImageSourceExtensions
                     if(length > 10_000_000)
                     {
                         await MessageBus.INSTANCE.SendError(new(Icons.Material.Filled.ImageNotSupported, TB("The local image file is too large (>10 MB). Skipping the image.")));
-                        return string.Empty;
+                        return (success: false, string.Empty);
                     }
 
                     var bytes = await File.ReadAllBytesAsync(image.Source, token);
-                    return Convert.ToBase64String(bytes);
+                    return (success: true, Convert.ToBase64String(bytes));
                 }
 
-                return string.Empty;
+                await MessageBus.INSTANCE.SendError(new(Icons.Material.Filled.ImageNotSupported, TB("The local image file does not exist. Skipping the image.")));
+                return (success: false, string.Empty);
             
             default:
-                return string.Empty;
+                return (success: false, string.Empty);
         }
     }
 }

app/MindWork AI Studio/Settings/DataModel/DataSourceERI_V1.cs

@@ -74,7 +74,9 @@ public readonly record struct DataSourceERI_V1 : IERIDataSource
                 LatestUserPrompt = lastUserPrompt switch
                 {
                     ContentText text => text.Text,
-                    ContentImage image => await image.AsBase64(token),
+                    ContentImage image => await image.TryAsBase64(token) is (success: true, { } base64Image)
+                        ? base64Image 
+                        : string.Empty,
                     _ => string.Empty
                 },
                 

app/MindWork AI Studio/Tools/RAG/IRetrievalContextExtensions.cs

@@ -81,7 +81,9 @@ public static class IRetrievalContextExtensions
                 sb.AppendLine();
                 sb.AppendLine("Matched image content as base64-encoded data:");
                 sb.AppendLine("````");
-                sb.AppendLine(await imageContext.AsBase64(token));
+                sb.AppendLine(await imageContext.TryAsBase64(token) is (success: true, { } base64Image)
+                        ? base64Image 
+                        : string.Empty);
                 sb.AppendLine("````");
                 break;