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

packages/backend/server/src/__tests__/copilot.e2e.ts

@@ -385,6 +385,45 @@ test('should create message correctly', async t => {
     t.truthy(messageId, 'should be able to create message with valid session');
   }
 
+  {
+    // with attachment url
+    {
+      const { id } = await createWorkspace(app);
+      const sessionId = await createCopilotSession(
+        app,
+        id,
+        randomUUID(),
+        promptName
+      );
+      const messageId = await createCopilotMessage(app, sessionId, undefined, [
+        'http://example.com/cat.jpg',
+      ]);
+      t.truthy(messageId, 'should be able to create message with url link');
+    }
+
+    // with attachment
+    {
+      const { id } = await createWorkspace(app);
+      const sessionId = await createCopilotSession(
+        app,
+        id,
+        randomUUID(),
+        promptName
+      );
+      const smallestPng =
+        'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAgAAAAIAQMAAAD+wSzIAAAABlBMVEX///+/v7+jQ3Y5AAAADklEQVQI12P4AIX8EAgALgAD/aNpbtEAAAAASUVORK5CYII';
+      const pngData = await fetch(smallestPng).then(res => res.arrayBuffer());
+      const messageId = await createCopilotMessage(
+        app,
+        sessionId,
+        undefined,
+        undefined,
+        [new File([new Uint8Array(pngData)], '1.png', { type: 'image/png' })]
+      );
+      t.truthy(messageId, 'should be able to create message with blobs');
+    }
+  }
+
   {
     await t.throwsAsync(
       createCopilotMessage(app, randomUUID()),