Restore the DB-less liveness fallback for event identities

A runtime whose database cannot be opened (the liveness smoke container
ships no writable SQLite scratch directory) raised
ImproperlyConfigured from _runtime_event_identity_snapshot and turned
/unified/ into a 500, breaking the container smoke gate. Fall back to
the build-time manifest identity snapshot for unavailable databases,
matching the existing query-forbidden fallbacks, and pin the behavior
with a regression test.

Author: alexeygrigorev

content/public_data.py

@@ -281,9 +281,10 @@ def _runtime_event_identity_snapshot() -> tuple[tuple[str, int, str], ...]:
             raise
         if isinstance(exc, RuntimeError) and "Database access not allowed" not in str(exc):
             raise
-        if isinstance(exc, (AssertionError, RuntimeError)):
-            return _manifest_event_identity_snapshot()
-        raise ImproperlyConfigured("Public Event UUID/public-ID mapping is unavailable.") from exc
+        # A runtime without a usable database (query-forbidden tests, the DB-less liveness
+        # container whose SQLite scratch directory is absent) serves the build-time manifest
+        # identities instead of failing every public page.
+        return _manifest_event_identity_snapshot()
 
 
 def _apply_runtime_event_public_paths(

events/tests/test_identity.py

@@ -6,8 +6,10 @@
 from copy import deepcopy
 from pathlib import Path
 from typing import ClassVar
+from unittest import mock
 
 from django.core.exceptions import ImproperlyConfigured
+from django.db import OperationalError
 from django.test import TestCase
 from django.urls import Resolver404, resolve
 
@@ -93,6 +95,22 @@ def test_manifest_rejects_missing_duplicate_and_renumbered_public_mappings(self)
         ):
             public_projection()
 
+    def test_unavailable_database_serves_the_manifest_identity_snapshot(self) -> None:
+        manifest = load_identity_manifest()
+        expected_paths = {item.canonical_path for item in manifest.events}
+
+        with mock.patch.object(
+            Event.objects,
+            "order_by",
+            side_effect=OperationalError("unable to open database file"),
+        ):
+            projection = public_projection()
+
+        self.assertEqual(
+            {event["public_path"] for event in projection["events"]},
+            expected_paths,
+        )
+
     def test_manifest_import_replay_is_byte_stable_and_a_preflight_noop(self) -> None:
         before = tuple(Event.objects.order_by("id").values_list("id", "public_id", "slug"))
         first = import_identity_manifest(dry_run=True)