Resolve all 46 low-severity architecture review findings

src/ZB.MOM.WW.ScadaBridge.KpiHistory/KpiSourceAdmission.cs

@@ -0,0 +1,33 @@
+using ZB.MOM.WW.ScadaBridge.Commons.Entities.Kpi;
+
+namespace ZB.MOM.WW.ScadaBridge.KpiHistory;
+
+/// <summary>
+/// Root-provider-owned admission for source collections. Actor replacement must not
+/// start another call while an earlier cancellation-ignoring collection still owns its scope.
+/// Registration indices are stable because the root provider's service collection is immutable.
+/// </summary>
+internal sealed class KpiSourceAdmission
+{
+    private readonly object _gate = new();
+    private readonly Dictionary<int, Task<IReadOnlyList<KpiSample>>> _tasks = new();
+
+    internal bool TryStart(
+        int registrationIndex,
+        Func<Task<IReadOnlyList<KpiSample>>> collect,
+        out Task<IReadOnlyList<KpiSample>> collection)
+    {
+        lock (_gate)
+        {
+            if (_tasks.TryGetValue(registrationIndex, out var existing) && !existing.IsCompleted)
+            {
+                collection = existing;
+                return false;
+            }
+
+            collection = Task.Run(collect);
+            _tasks[registrationIndex] = collection;
+            return true;
+        }
+    }
+}