Protect published snapshots and concurrent edits

apps/content/tests/integration/test_services.py

@@ -1,10 +1,13 @@
 import io
+from concurrent.futures import ThreadPoolExecutor
+from threading import Barrier
 
 import pytest
 from django.contrib.auth.models import Group, Permission
 from django.core.exceptions import ValidationError
 from django.core.exceptions import PermissionDenied
 from django.core.files.uploadedfile import SimpleUploadedFile
+from django.db import connection, connections, close_old_connections
 from PIL import Image
 
 from apps.content.models import EditorialPage, MediaAsset, PageRevision, PublicationAudit, SiteIdentity
@@ -103,6 +106,34 @@ def test_stale_publish_is_rejected_without_swapping_pointer():
     assert second.status == "draft"
 
 
+@pytest.mark.django_db(transaction=True)
+@pytest.mark.skipif(connection.vendor != "postgresql", reason="SQLite has no row-level select_for_update locking")
+def test_concurrent_publish_only_one_revision_wins():
+    page = EditorialPage.objects.create(slug="home", page_kind="sections")
+    user = actor("chief", superuser=True)
+    drafts = [save_page_draft(user, page, page_fields(title), home_sections()) for title in ("First", "Second")]
+    barrier = Barrier(3)
+
+    def attempt(revision_id):
+        close_old_connections()
+        barrier.wait()
+        try:
+            publish_page(user, PageRevision.objects.get(pk=revision_id), expected_published_id=None)
+            return "published"
+        except PublishConflict:
+            return "conflict"
+        finally:
+            connections.close_all()
+
+    with ThreadPoolExecutor(max_workers=2) as pool:
+        futures = [pool.submit(attempt, draft.pk) for draft in drafts]
+        barrier.wait()
+        outcomes = [future.result(timeout=15) for future in futures]
+    assert sorted(outcomes) == ["conflict", "published"]
+    page.refresh_from_db()
+    assert page.published_revision_id in {draft.pk for draft in drafts}
+
+
 def test_publish_rejects_incomplete_page_and_leaves_no_public_content():
     page = EditorialPage.objects.create(slug="home", page_kind="sections")
     user = actor("chief", superuser=True)
@@ -181,3 +212,7 @@ def test_revision_sections_and_audit_are_immutable():
     audit.operation = "publish"
     with pytest.raises(ValidationError):
         audit.save()
+    published = publish_page(user, PageRevision.objects.get(pk=draft.pk), expected_published_id=None)
+    published.status = "draft"
+    with pytest.raises(ValidationError):
+        published.save()