fix(centralui): cap retained event-log rows; hint keyword search 7-day window (review 2026-10-21 07/M-3, lane D follow-up)

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

@@ -24,6 +24,9 @@
     <ToastNotification @ref="_toast" />
 
     <div class="collapse show" id="event-logs-filters">
+        <div class="form-text mb-1" id="filter-keyword-hint">
+            Keyword search covers at most the last 7 days unless a narrower From/To is set.
+        </div>
         <div class="row mb-3 g-2 align-items-end">
             <div class="col-md-2">
                 <label class="form-label small" for="filter-site">Site</label>
@@ -67,6 +70,7 @@
                        type="text"
                        class="form-control form-control-sm"
                        aria-label="Message contains"
+                       aria-describedby="filter-keyword-hint"
                        @bind="_filterKeyword" />
             </div>
             <div class="col-md-2">
@@ -152,7 +156,13 @@
         </table>
 
         <div class="d-flex justify-content-between align-items-center">
-            <span class="text-muted small">Showing @_entries.Count entries</span>
+            <span class="text-muted small">
+                Showing @_entries.Count entries
+                @if (_droppedCount > 0)
+                {
+                    <text>(oldest @_droppedCount dropped — display is capped at @MaxRetainedRows rows)</text>
+                }
+            </span>
             <div>
                 @if (_hasMore)
                 {
@@ -194,6 +204,26 @@
     // moved every expansion onto the wrong row. The id is stable by construction.
     private readonly HashSet<string> _expandedRows = new();
 
+    /// <summary>Ceiling on rows retained across "Load more" pages (review 2026-10-21 07/M-3).</summary>
+    internal const int MaxRetainedRows = 1000;
+
+    private int _droppedCount;
+
+    /// <summary>
+    /// Appends a page to the retained list, dropping the oldest (head) rows beyond
+    /// <paramref name="cap"/> and un-expanding any dropped row. Returns the number dropped.
+    /// </summary>
+    internal static int AppendCapped(
+        List<EventLogEntry> entries, IEnumerable<EventLogEntry> page, HashSet<string> expandedRows, int cap)
+    {
+        entries.AddRange(page);
+        var excess = entries.Count - cap;
+        if (excess <= 0) return 0;
+        foreach (var dropped in entries.Take(excess)) expandedRows.Remove(dropped.Id);
+        entries.RemoveRange(0, excess);
+        return excess;
+    }
+
     private int ActiveFilterCount
     {
         get
@@ -225,6 +255,7 @@
     private async Task Search()
     {
         _entries = new();
+        _droppedCount = 0;
         _continuationToken = null;
         _expandedRows.Clear();
         await FetchPage();
@@ -276,7 +307,7 @@
             if (response.Success)
             {
                 _entries ??= new();
-                _entries.AddRange(response.Entries);
+                _droppedCount += AppendCapped(_entries, response.Entries, _expandedRows, MaxRetainedRows);
                 _hasMore = response.HasMore;
                 _continuationToken = response.ContinuationToken;
             }

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

@@ -0,0 +1,71 @@
+using Bunit;
+using Microsoft.AspNetCore.Components.Authorization;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using NSubstitute;
+using System.Security.Claims;
+using ZB.MOM.WW.ScadaBridge.CentralUI.Auth;
+using ZB.MOM.WW.ScadaBridge.CentralUI.Components.Pages.Monitoring;
+using ZB.MOM.WW.ScadaBridge.Commons.Entities.Sites;
+using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
+using ZB.MOM.WW.ScadaBridge.Commons.Messages.RemoteQuery;
+using ZB.MOM.WW.ScadaBridge.Communication;
+
+namespace ZB.MOM.WW.ScadaBridge.CentralUI.Tests.Monitoring;
+
+/// <summary>Review 2026-10-21 07/M-3 (retained-row cap) and the lane D keyword-window hint.</summary>
+public class EventLogsPageTests : BunitContext
+{
+    private static EventLogEntry Entry(int n) =>
+        new($"id-{n}", DateTimeOffset.UnixEpoch.AddSeconds(n), "T", "Info", null, "src", "m", null);
+
+    private static List<EventLogEntry> Page(int from, int count) =>
+        Enumerable.Range(from, count).Select(Entry).ToList();
+
+    /// <summary>Rows beyond the cap are dropped from the head and their expansion state cleared.</summary>
+    [Fact]
+    public void AppendCapped_DropsOldestRowsBeyondCap_AndUnexpandsThem()
+    {
+        var entries = Page(0, 8);
+        var expanded = new HashSet<string> { "id-0", "id-7" };
+
+        var dropped = EventLogs.AppendCapped(entries, Page(8, 4), expanded, cap: 10);
+
+        Assert.Equal(2, dropped);
+        Assert.Equal(10, entries.Count);
+        Assert.Equal("id-2", entries[0].Id);
+        Assert.Equal("id-11", entries[^1].Id);
+        Assert.DoesNotContain("id-0", expanded);
+        Assert.Contains("id-7", expanded);
+    }
+
+    /// <summary>Under the cap nothing is dropped.</summary>
+    [Fact]
+    public void AppendCapped_UnderCap_KeepsEverything()
+    {
+        var entries = Page(0, 3);
+        Assert.Equal(0, EventLogs.AppendCapped(entries, Page(3, 3), new HashSet<string>(), cap: 10));
+        Assert.Equal(6, entries.Count);
+    }
+
+    /// <summary>The page tells operators the keyword search window is bounded.</summary>
+    [Fact]
+    public void Page_ShowsKeywordWindowHint()
+    {
+        var identity = new ClaimsIdentity(new[] { new Claim(ClaimTypes.Name, "u") }, "T");
+        var auth = Substitute.For<AuthenticationStateProvider>();
+        auth.GetAuthenticationStateAsync().Returns(new AuthenticationState(new ClaimsPrincipal(identity)));
+        Services.AddSingleton(auth);
+        Services.AddScoped(_ => new SiteScopeService(auth));
+        var siteRepo = Substitute.For<ISiteRepository>();
+        siteRepo.GetAllSitesAsync().Returns(new List<Site>());
+        Services.AddSingleton(siteRepo);
+        Services.AddSingleton(new CommunicationService(
+            Options.Create(new CommunicationOptions()), NullLogger<CommunicationService>.Instance));
+
+        var cut = Render<EventLogs>();
+
+        Assert.Contains("at most the last 7 days", cut.Markup);
+    }
+}