Fix throttling issue with preview actor (baserow#6078)

Author: jrmi

backend/src/baserow/contrib/builder/preview/__init__.py

@@ -43,6 +43,7 @@ class BuilderPreviewActor:
 
     is_authenticated = True
     is_anonymous = False
+    is_staff = False
     user_source_authentication_header = "Authorization"
 
     @property

backend/tests/baserow/throttling/test_builder_preview_throttle.py

@@ -0,0 +1,32 @@
+import pytest
+from rest_framework.request import Request
+from rest_framework.test import APIRequestFactory
+
+from baserow.api.exceptions import ThrottledAPIException
+from baserow.contrib.builder.preview import BuilderPreviewActor
+from baserow.throttling.handler import ConcurrentUserRequestsThrottle
+
+
+def test_builder_preview_requests_are_throttled_and_release_their_slot(
+    settings, monkeypatch
+):
+    """Preview actors obey the concurrency limit and free their slot after a response."""
+
+    settings.BASEROW_THROTTLE_BLACKLIST_TTL_SECONDS = 0
+    monkeypatch.setattr(ConcurrentUserRequestsThrottle, "rate", 1, raising=False)
+    actor = BuilderPreviewActor(
+        builder_id=1, workspace_id=1, grant_id=12345, issued_by_user_id=1
+    )
+    request = Request(APIRequestFactory().get("/api/builder/preview/1/current/"))
+    request.user = actor
+
+    throttle = ConcurrentUserRequestsThrottle()
+    assert throttle.allow_request(request, None)
+    try:
+        with pytest.raises(ThrottledAPIException):
+            ConcurrentUserRequestsThrottle().allow_request(request, None)
+    finally:
+        ConcurrentUserRequestsThrottle.on_request_processed(request._request)
+
+    assert ConcurrentUserRequestsThrottle().allow_request(request, None)
+    ConcurrentUserRequestsThrottle.on_request_processed(request._request)

changelog/entries/unreleased/bug/fix_builder_preview_with_concurrency_throttling.json

@@ -0,0 +1,9 @@
+{
+    "type": "bug",
+    "message": "Fixed Application Builder previews failing when concurrent request throttling is enabled.",
+    "issue_origin": "github",
+    "issue_number": null,
+    "domain": "builder",
+    "bullet_points": [],
+    "created_at": "2026-09-14"
+}