diff --git a/src/servers/api/upload/upload.ts b/src/servers/api/upload/upload.ts
index b7cb970f..c932ec6f 100644
--- a/src/servers/api/upload/upload.ts
+++ b/src/servers/api/upload/upload.ts
@@ -2,6 +2,7 @@ import { createRouter } from '../../create-router';
 import { mkdir } from 'node:fs/promises';
 import { join } from 'node:path';
 import { getTmpAttachmentsDir, getAttachmentsDir } from '@@/data-path';
+import { writeAtomic } from '@@/write-atomic';
 
 const MAX_FILE_SIZE = 5 * 1024 * 1024; // 5 MB
 /** PDFs never enter a prompt whole — the agent reads them from disk — so the ceiling is storage, not context. */
@@ -49,8 +50,7 @@ uploadRouter.post('/', async (ctx) => {
       saveDir = getTmpAttachmentsDir(user.email);
     }
 
-    await mkdir(saveDir, { recursive: true });
-    await Bun.write(join(saveDir, filename), buffer);
+    await writeAtomic(join(saveDir, filename), buffer);
 
     // Only an image gets a data URL. Building one for a PDF would mean carrying megabytes through the
     // browser for a preview nothing renders.