fix(server): empty mimetype attachments fallback (#11869)

packages/backend/server/src/plugins/copilot/providers/fal.ts

@@ -138,7 +138,15 @@ export class FalProvider
     );
     return {
       model_name: options.modelName || undefined,
-      image_url: attachments?.[0],
+      image_url: attachments
+        ?.map(v =>
+          typeof v === 'string'
+            ? v
+            : v.mimeType.startsWith('image/')
+              ? v.attachment
+              : undefined
+        )
+        .filter(v => !!v)[0],
       prompt: content.trim(),
       loras: lora.length ? lora : undefined,
       controlnets: controlnets.length ? controlnets : undefined,