fix(ui): Alarm Summary poll defers row rebuilds to the live path while IsLive (plan R2-07 T8)

docs/requirements/Component-CentralUI.md

@@ -191,7 +191,7 @@ Per-leaf alarm rendering (leaf nodes are individual conditions for native alarms
 - **Live updates** — the page is driven by a **transient, per-site central live alarm cache** (`ISiteAlarmLiveCache`, owned by the Communication component; see [Component-Communication](Component-Communication.md)). On site select the page subscribes to the cache; the cache runs one shared, reference-counted per-site aggregator that **seeds** from the snapshot fan-out and then stays warm on a single **site-wide, alarm-only** `SubscribeSite` gRPC stream (seed-then-stream, dedup by `(InstanceUniqueName, AlarmName, SourceReference)`). Applied deltas raise an in-process change event (mirroring `IDeploymentStatusNotifier`) that the Blazor circuit pushes to the browser via `StateHasChanged()` — no new SignalR hub. `AlarmSummaryService.BuildFromLiveAlarms` rebuilds the roll-up + rows from the cache's current alarm set. The cache is **purely in-memory on the active central node** — there is still **no persisted central alarm store**; on a NodeA↔NodeB failover the new active node re-seeds from scratch.
 - **View** — roll-up tiles (total active, worst severity, unacked count, per-`AlarmKind` counts) plus a flat, sortable, filterable table. Filters cover instance, `AlarmKind` (Computed / NativeOpcUa / NativeMxAccess), state, acked/unacked, severity threshold, and name search.
 - **Read-only** — there are no ack / shelve / suppress controls (native alarms remain read-only by design).
-- **Refresh** — manual refresh button plus the 15s poll timer (mirroring the Health dashboard), now retained as a **fallback + `NotReporting` authority** behind the live cache: when the cache reports `IsLive`, the page renders live-cache state; when a stream is unhealthy or a site has not yet seeded, the poll keeps the page fresh so a stream failure never blanks it. (Aggregated live stream **delivered 2026-07-10** — see `docs/plans/2026-07-10-aggregated-live-alarm-stream-plan.md`.)
+- **Refresh** — manual refresh button plus the 15s poll timer (mirroring the Health dashboard), now retained as a **fallback + `NotReporting` authority** behind the live cache: when the cache reports `IsLive`, the page renders live-cache state; when a stream is unhealthy or a site has not yet seeded, the poll keeps the page fresh so a stream failure never blanks it. When live, the poll updates only the `NotReporting` list and leaves the row set to the delta path, so a slow fan-out can never momentarily revert a fresher live delta (R2 N5). (Aggregated live stream **delivered 2026-07-10** — see `docs/plans/2026-07-10-aggregated-live-alarm-stream-plan.md`.)
 - **Reuse** — the alarm badge/formatter markup is factored out of Debug View into a shared `AlarmStateBadges` component consumed by both Debug View and this page.
 
 ### Parked Message Management (Deployment Role)

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Monitoring/AlarmSummary.razor

@@ -298,9 +298,20 @@
             {
                 return;
             }
-            _rows = result.Alarms;
+
+            // _notReporting is the poll's unique authority — the alarm-only live cache
+            // cannot compute it — so it is always refreshed.
             _notReporting = result.NotReportingInstances;
-            _rollup = AlarmSummaryService.ComputeRollup(_rows);
+
+            // While the cache is live, the live deltas own the row set: a poll whose fan-out
+            // started BEFORE a delta must not land after it and momentarily revert the alarm
+            // state (arch-review R2 N5). When not live (pre-seed / degraded stream / dead
+            // aggregator — see R2 N6), the poll remains the full-rebuild safety net.
+            if (!LiveAlarmCache.IsLive(siteId))
+            {
+                _rows = result.Alarms;
+                _rollup = AlarmSummaryService.ComputeRollup(_rows);
+            }
             RecomputeVisibleRows();
         }
         catch
@@ -348,10 +359,11 @@
     //     aggregated alarm set changes. We rebuild _rows/_rollup/_visibleRows from the
     //     immutable live snapshot — but deliberately DO NOT touch _notReporting, since
     //     the alarm-only live cache can't compute it.
-    //   • The 15s poll (RefreshAsync) still runs untouched: it is the authority for
-    //     _notReporting and the safety net when the cache is not live (pre-seed or a
-    //     degraded/failed stream — IsLive == false). When live, the poll simply
-    //     re-affirms the same snapshot; the live path just makes updates arrive sooner.
+    //   • The 15s poll (RefreshAsync) is the authority for _notReporting and the
+    //     full-rebuild safety net ONLY while the cache is not live (pre-seed or a
+    //     degraded/failed stream — IsLive == false); when live it deliberately leaves
+    //     _rows to the delta path, so a slow fan-out can never revert a fresher live
+    //     delta (arch-review R2 N5).
     //   • Both paths mutate shared state only via the Blazor dispatcher (the poll via
     //     its InvokeAsync callback, the live delta via OnLiveChanged's InvokeAsync), so
     //     they are serialized and never race. Each rebuild is an idempotent snapshot, so

tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Monitoring/AlarmSummaryRenderTests.cs

@@ -244,6 +244,40 @@ public class AlarmSummaryRenderTests : BunitContext
         });
     }
 
+    // ── arch-review R2 N5: while live, the poll updates only _notReporting ──────
+
+    [Fact]
+    public void PollWhileLive_UpdatesNotReportingOnly_DoesNotRegressLiveRows()
+    {
+        // Poll snapshot = Zeta/Alpha (constructor stub) + a not-reporting instance.
+        _summary.GetSiteAlarmsAsync(Arg.Any<int>(), Arg.Any<CancellationToken>())
+            .Returns(ci => Task.FromResult(new AlarmSummaryResult(
+                new List<AlarmSummaryRow>
+                {
+                    new("Zeta", new AlarmStateChanged("Zeta", "Z-alarm", AlarmState.Active, 900, DateTimeOffset.UtcNow)),
+                },
+                new[] { "OfflineInstance" })));
+
+        var cut = RenderWithSiteSelected();
+
+        // Go live with a fresher delta: Gamma only (arch-review R2 N5).
+        _liveCache.PushAlarms(new List<AlarmStateChanged>
+        {
+            new("Gamma", "G-alarm", AlarmState.Active, 300, DateTimeOffset.UtcNow),
+        });
+        cut.WaitForAssertion(() => Assert.Equal("Gamma", FirstRowInstance(cut)));
+
+        // A poll now completes: it owns _notReporting but must NOT rebuild the rows.
+        cut.Find("[data-test='alarm-summary-refresh']").Click();
+
+        cut.WaitForAssertion(() =>
+        {
+            Assert.Contains("OfflineInstance", cut.Markup);            // notReporting refreshed
+            Assert.Equal("Gamma", FirstRowInstance(cut));              // live rows NOT regressed
+            Assert.Single(cut.FindAll("tr[data-test='alarm-summary-row']"));
+        });
+    }
+
     /// <summary>
     /// Controllable in-memory fake of <see cref="ISiteAlarmLiveCache"/>: records
     /// subscribe/dispose counts and lets a test push a live snapshot (which flips