DiffViewer refactor — 6-section plugin pattern + 1000-row cap. Closes task #156 (Phase 6.4 Stream C). Replaces the flat single-table rendering that mixed Namespace/DriverInstance/Equipment/Tag rows into one untyped list with a per-section-card layout that makes draft review actually scannable on non-trivial diffs. New DiffSection.razor reusable component encapsulates the per-section rendering — card header shows Title + Description + a three-badge summary (+added / −removed / ~modified plus a "no changes" grey badge when the section is empty) so operators can glance at a six-card page and see what areas of the draft actually shifted before drilling into any one table. Hard row-cap at DefaultRowCap=1000 per section lives inside the component so a pathological draft (e.g. 20k tags churned by a block rebuild) can't freeze the browser on render — excess rows are silently dropped with a yellow warning banner that surfaces "Showing the first 1000 of N rows" + a pointer to run sp_ComputeGenerationDiff directly for the full set. Body max-height: 400px + overflow-y: auto gives each section its own scroll region so one big section doesn't push the others off screen. DiffViewer.razor refactored to a static Sections table driving a single foreach that instantiates one DiffSection per known TableName. Sections listed in author-order (Namespace → DriverInstance → Equipment → Tag → UnsLine → NodeAcl) — six entries matching the task acceptance criterion. The first four correspond to what sp_ComputeGenerationDiff currently emits; the last two (UnsLine + NodeAcl) render as empty "no changes" cards today + will light up when the proc is extended (tracked in task #196 for NodeAcl; UnsLine proc extension is a natural follow-up since UnsImpactAnalyzer already tracks UNS moves). RowsFor(tableName) replaces the prior flat table — each section filters the overall DiffRow list by its TableName so the proc output format stays stable. Header-bar summary at the top of the page now reads "N rows across M of 6 sections" so operators see overall change weight at a glance before scanning. Two Razor-specific fixes landed along the way: loop variable renamed from section to sec because @section collides with the Razor section directive + trips RZ2005; helper method renamed from Group to RowsFor because the Razor generator gets confused by a parameter-flowing method whose name clashes with LINQ's Group extension (the source-gen output referenced TypeCheck<T> with no argument). Admin project builds 0 errors; Admin.Tests suite 76/76 (unchanged — the refactor is structural + no service-layer logic changed, so the existing DraftValidator + EquipmentService + AdminServicesIntegrationTests cover the consuming paths). No bUnit in this project so the cap behavior isn't unit-tested at the component level; DiffSection.OnParametersSet is small + deterministic (int counts + Take(RowCap)) + reviewed before ship.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.OtOpcUa.Admin/Components/Pages/Clusters/DiffSection.razor

@@ -0,0 +1,90 @@
+@using ZB.MOM.WW.OtOpcUa.Admin.Services
+
+@* Per-section diff renderer — the base used by DiffViewer for every known TableName. Caps
+   output at RowCap rows so a pathological draft (e.g. 20k tags churned) can't freeze the
+   Blazor render; overflow banner tells operator how many rows were hidden. *@
+
+<div class="card mb-3">
+    <div class="card-header d-flex justify-content-between align-items-center">
+        <div>
+            <strong>@Title</strong>
+            <small class="text-muted ms-2">@Description</small>
+        </div>
+        <div>
+            @if (_added > 0) { <span class="badge bg-success me-1">+@_added</span> }
+            @if (_removed > 0) { <span class="badge bg-danger me-1">−@_removed</span> }
+            @if (_modified > 0) { <span class="badge bg-warning text-dark me-1">~@_modified</span> }
+            @if (_total == 0) { <span class="badge bg-secondary">no changes</span> }
+        </div>
+    </div>
+    @if (_total == 0)
+    {
+        <div class="card-body text-muted small">No changes in this section.</div>
+    }
+    else
+    {
+        @if (_total > RowCap)
+        {
+            <div class="alert alert-warning mb-0 small rounded-0">
+                Showing the first @RowCap of @_total rows — cap protects the browser from megabyte-class
+                diffs. Inspect the remainder via the SQL <code>sp_ComputeGenerationDiff</code> directly.
+            </div>
+        }
+        <div class="table-responsive" style="max-height: 400px; overflow-y: auto;">
+            <table class="table table-sm table-hover mb-0">
+                <thead class="table-light">
+                    <tr><th>LogicalId</th><th style="width: 120px;">Change</th></tr>
+                </thead>
+                <tbody>
+                @foreach (var r in _visibleRows)
+                {
+                    <tr>
+                        <td><code>@r.LogicalId</code></td>
+                        <td>
+                            @switch (r.ChangeKind)
+                            {
+                                case "Added":    <span class="badge bg-success">@r.ChangeKind</span> break;
+                                case "Removed":  <span class="badge bg-danger">@r.ChangeKind</span> break;
+                                case "Modified": <span class="badge bg-warning text-dark">@r.ChangeKind</span> break;
+                                default:         <span class="badge bg-secondary">@r.ChangeKind</span> break;
+                            }
+                        </td>
+                    </tr>
+                }
+                </tbody>
+            </table>
+        </div>
+    }
+</div>
+
+@code {
+    /// <summary>Default row-cap per section — matches task #156's acceptance criterion.</summary>
+    public const int DefaultRowCap = 1000;
+
+    [Parameter, EditorRequired] public string Title { get; set; } = string.Empty;
+    [Parameter] public string Description { get; set; } = string.Empty;
+    [Parameter, EditorRequired] public IReadOnlyList<DiffRow> Rows { get; set; } = [];
+    [Parameter] public int RowCap { get; set; } = DefaultRowCap;
+
+    private int _total;
+    private int _added;
+    private int _removed;
+    private int _modified;
+    private List<DiffRow> _visibleRows = [];
+
+    protected override void OnParametersSet()
+    {
+        _total = Rows.Count;
+        _added = 0; _removed = 0; _modified = 0;
+        foreach (var r in Rows)
+        {
+            switch (r.ChangeKind)
+            {
+                case "Added":    _added++;    break;
+                case "Removed":  _removed++;  break;
+                case "Modified": _modified++; break;
+            }
+        }
+        _visibleRows = _total > RowCap ? Rows.Take(RowCap).ToList() : Rows.ToList();
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Admin/Components/Pages/Clusters/DiffViewer.razor

@@ -28,36 +28,44 @@ else if (_rows.Count == 0)
 }
 else
 {
-    <table class="table table-hover table-sm">
+    <p class="small text-muted mb-3">
-        <thead><tr><th>Table</th><th>LogicalId</th><th>ChangeKind</th></tr></thead>
+        @_rows.Count row@(_rows.Count == 1 ? "" : "s") across @_sectionsWithChanges of @Sections.Count sections.
-        <tbody>
+        Each section is capped at @DiffSection.DefaultRowCap rows to keep the browser responsive on pathological drafts.
-        @foreach (var r in _rows)
+    </p>
-        {
+
-            <tr>
+    @foreach (var sec in Sections)
-                <td>@r.TableName</td>
+    {
-                <td><code>@r.LogicalId</code></td>
+        <DiffSection Title="@sec.Title"
-                <td>
+                     Description="@sec.Description"
-                    @switch (r.ChangeKind)
+                     Rows="@RowsFor(sec.TableName)"/>
-                    {
+    }
-                        case "Added":    <span class="badge bg-success">@r.ChangeKind</span> break;
-                        case "Removed":  <span class="badge bg-danger">@r.ChangeKind</span> break;
-                        case "Modified": <span class="badge bg-warning text-dark">@r.ChangeKind</span> break;
-                        default:         <span class="badge bg-secondary">@r.ChangeKind</span> break;
-                    }
-                </td>
-            </tr>
-        }
-        </tbody>
-    </table>
 }
 
 @code {
     [Parameter] public string ClusterId { get; set; } = string.Empty;
     [Parameter] public long GenerationId { get; set; }
 
+    /// <summary>
+    ///     Ordered section definitions — each maps a <c>TableName</c> emitted by
+    ///     <c>sp_ComputeGenerationDiff</c> to a human label + description. The proc currently
+    ///     emits Namespace/DriverInstance/Equipment/Tag; UnsLine + NodeAcl entries render as
+    ///     empty "no changes" cards until the proc is extended (tracked in tasks #196 + #156
+    ///     follow-up). Six sections total matches the task #156 target.
+    /// </summary>
+    private static readonly IReadOnlyList<SectionDef> Sections = new[]
+    {
+        new SectionDef("Namespace",      "Namespaces",      "OPC UA namespace URIs + enablement"),
+        new SectionDef("DriverInstance", "Driver instances","Per-cluster driver configuration rows"),
+        new SectionDef("Equipment",      "Equipment",       "UNS level-5 rows + identification fields"),
+        new SectionDef("Tag",            "Tags",            "Per-device tag definitions + poll-group binding"),
+        new SectionDef("UnsLine",        "UNS structure",   "Site / Area / Line hierarchy (proc-extension pending)"),
+        new SectionDef("NodeAcl",        "ACLs",            "LDAP-group → node-scope permission grants (proc-extension pending)"),
+    };
+
     private List<DiffRow>? _rows;
     private string _fromLabel = "(empty)";
     private string? _error;
+    private int _sectionsWithChanges;
 
     protected override async Task OnParametersSetAsync()
     {
@@ -67,7 +75,13 @@ else
             var from = all.FirstOrDefault(g => g.Status == GenerationStatus.Published);
             _fromLabel = from is null ? "(empty)" : $"gen {from.GenerationId}";
             _rows = await GenerationSvc.ComputeDiffAsync(from?.GenerationId ?? 0, GenerationId, CancellationToken.None);
+            _sectionsWithChanges = Sections.Count(s => _rows.Any(r => r.TableName == s.TableName));
         }
         catch (Exception ex) { _error = ex.Message; }
     }
+
+    private IReadOnlyList<DiffRow> RowsFor(string tableName) =>
+        _rows?.Where(r => r.TableName == tableName).ToList() ?? [];
+
+    private sealed record SectionDef(string TableName, string Title, string Description);
 }