fixed image previews

backend/routes/upload.js

@@ -4,6 +4,7 @@ const { authenticateToken } = require("../middleware/auth");
 const { uploadPresignLimiter } = require("../middleware/rateLimiter");
 const s3Service = require("../services/s3Service");
 const S3OwnershipService = require("../services/s3OwnershipService");
+const { v4: uuidv4 } = require("uuid");
 const logger = require("../utils/logger");
 const MAX_BATCH_SIZE = 20;
 
@@ -63,6 +64,7 @@ router.post(
 /**
  * POST /api/upload/presign-batch
  * Get presigned URLs for uploading multiple files to S3
+ * All files in a batch share the same UUID base for coordinated variant uploads
  */
 router.post(
   "/presign-batch",
@@ -96,13 +98,17 @@ router.post(
         }
       }
 
+      // Generate one shared UUID for all files in this batch
+      const sharedBaseKey = uuidv4();
+
       const results = await Promise.all(
         files.map((f) =>
           s3Service.getPresignedUploadUrl(
             uploadType,
             f.contentType,
             f.fileName,
-            f.fileSize
+            f.fileSize,
+            sharedBaseKey
           )
         )
       );
@@ -111,9 +117,10 @@ router.post(
         userId: req.user.id,
         uploadType,
         count: results.length,
+        baseKey: sharedBaseKey,
       });
 
-      res.json({ uploads: results });
+      res.json({ uploads: results, baseKey: sharedBaseKey });
     } catch (error) {
       if (error.message.includes("Invalid")) {
         return res.status(400).json({ error: error.message });