fix: make default initialization concurrency-safe

JobTrackerApi/Services/ApplicationChecklistService.cs

@@ -357,6 +357,7 @@ public sealed class ApplicationChecklistService : IApplicationChecklistService
         var missing = Defaults.Where(t => !existing.Contains(t.Key)).ToList();
         if (missing.Count == 0) return items;
 
+        var seeded = new List<ApplicationChecklistItem>(missing.Count);
         var order = 0;
         foreach (var template in Defaults)
         {
@@ -377,12 +378,27 @@ public sealed class ApplicationChecklistService : IApplicationChecklistService
                 };
                 _db.ApplicationChecklistItems.Add(item);
                 items.Add(item);
+                seeded.Add(item);
             }
             order++;
         }
 
-        await _db.SaveChangesAsync(ct);
-        return items;
+        try
+        {
+            await _db.SaveChangesAsync(ct);
+            return items;
+        }
+        catch (DbUpdateException)
+        {
+            foreach (var item in seeded) _db.Entry(item).State = EntityState.Detached;
+
+            var persisted = await LoadItemsAsync(ownerUserId, jobApplicationId, ct);
+            var persistedKeys = persisted.Where(i => i.SystemKey is not null)
+                .Select(i => i.SystemKey!)
+                .ToHashSet(StringComparer.Ordinal);
+            if (missing.Any(template => !persistedKeys.Contains(template.Key))) throw;
+            return persisted;
+        }
     }
 
     private async Task SyncAutoCompletionAsync(List<ApplicationChecklistItem> items, ChecklistSignals signals, CancellationToken ct)