Fix role setting for assistant-sent images in Anthropic API

Anthropic API does not support assistants sending images directly, so the role is adjusted to "user" for such messages. This ensures compatibility and prevents errors when processing image messages.

anthropic.go

@@ -71,6 +71,11 @@ func (a anthropic) requestToAnthropicRequest(req Request) anth.MessagesRequest {
 			}
 
 			for _, img := range msg.Images {
+				// anthropic doesn't allow the assistant to send images, so we need to say it's from the user
+				if m.Role == anth.RoleAssistant {
+					m.Role = anth.RoleUser
+				}
+
 				if img.Base64 != "" {
 					m.Content = append(m.Content, anth.NewImageMessageContent(
 						anth.NewMessageContentSource(