UnsTab native HTML5 drag/drop + 409 concurrent-edit modal + optimistic-concurrency commit path. Closes UI slice of task #153 (Phase 6.4 Stream A UI follow-up). Playwright E2E smoke is split into new task #199 — Playwright install + WebApplicationFactory + seeded-DB harness is genuinely its own infra-setup PR. Native HTML5 attributes (draggable, @ondragstart, @ondragover, @ondragleave, @ondrop) deliberately over MudBlazor per the task title — no MudBlazor ever joins this project. Two new service methods on UnsService land the data layer the existing UnsImpactAnalyzer assumed but which didn't actually exist: (1) LoadSnapshotAsync(generationId) — walks UnsAreas + UnsLines + per-line equipment counts + builds a UnsTreeSnapshot including a 16-char SHA-256 revision token computed deterministically over the sorted (kind, id, parent, name, notes) tuple-set so it's stable across processes + changes whenever any row is added / modified / deleted; (2) MoveLineAsync(generationId, expectedToken, lineId, targetAreaId) — re-parents one line inside the same draft under an EF transaction, recomputes the current revision token from freshly-loaded rows, and throws DraftRevisionConflictException when the caller-supplied token no longer matches. Token mismatch means another operator mutated the draft between preview + commit + the move rolls back rather than clobbering their work. No-op same-area drop is a silent return. Cross-generation move is prevented by the generationId filter on the transaction reads. UnsTab.razor gains draggable="true" on every line row with @ondragstart capturing the LineId into _dragLineId, and every area row is a drop target (@ondragover with :preventDefault so the browser accepts drops, @ondrop kicking off OnLineDroppedAsync). Drop path loads a fresh snapshot, builds a UnsMoveOperation(Kind=LineMove, source/target cluster matching because cross-cluster is decision-#82 rejected), runs UnsImpactAnalyzer.Analyze + shows a Bootstrap modal rendered inline in the component — modal shows HumanReadableSummary + equipment/tag counts + any CascadeWarnings list. Confirm button calls MoveLineAsync with the snapshot's RevisionToken; DraftRevisionConflictException surfaces a separate red-header "Draft changed — refresh required" modal with a Reload button that re-fetches areas + lines from the DB. New DraftRevisionConflictException in UnsService.cs, co-located with the service that throws it. Five new UnsServiceMoveTests covering LoadSnapshotAsync (areas + lines + equipment counts), RevisionToken stability between two reads, RevisionToken changes on AddLineAsync, MoveLineAsync happy path reparents the line in the DB, MoveLineAsync with stale token throws DraftRevisionConflictException + leaves the DB unchanged. Admin suite 81/81 passing (was 76, +5). Admin project builds 0 errors. Task #199 captures the deferred Playwright E2E smoke — drag a line onto a different area in a real browser, assert preview modal contents, click Confirm, assert the line row shows the new area. That PR stands up a new tests/ZB.MOM.WW.OtOpcUa.Admin.E2ETests project with Playwright + WebApplicationFactory + seeded InMemory DbContext.

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

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

@@ -2,6 +2,13 @@
 @using ZB.MOM.WW.OtOpcUa.Configuration.Entities
 @inject UnsService UnsSvc
 
+<div class="alert alert-info small mb-3">
+    Drag any line in the <strong>UNS Lines</strong> table onto an area row in <strong>UNS Areas</strong>
+    to re-parent it. A preview modal shows the impact (equipment re-home count) + lets you confirm
+    or cancel. If another operator modifies the draft while you're confirming, you'll see a 409
+    refresh-required modal instead of clobbering their work.
+</div>
+
 <div class="row">
     <div class="col-md-6">
         <div class="d-flex justify-content-between mb-2">
@@ -14,11 +21,20 @@
         else
         {
             <table class="table table-sm">
-                <thead><tr><th>AreaId</th><th>Name</th></tr></thead>
+                <thead><tr><th>AreaId</th><th>Name</th><th class="small text-muted">(drop target)</th></tr></thead>
                 <tbody>
                 @foreach (var a in _areas)
                 {
-                    <tr><td><code>@a.UnsAreaId</code></td><td>@a.Name</td></tr>
+                    <tr class="@(_hoverAreaId == a.UnsAreaId ? "table-primary" : "")"
+                        @ondragover="e => OnAreaDragOver(e, a.UnsAreaId)"
+                        @ondragover:preventDefault
+                        @ondragleave="() => _hoverAreaId = null"
+                        @ondrop="() => OnLineDroppedAsync(a.UnsAreaId)"
+                        @ondrop:preventDefault>
+                        <td><code>@a.UnsAreaId</code></td>
+                        <td>@a.Name</td>
+                        <td class="small text-muted">drop here</td>
+                    </tr>
                 }
                 </tbody>
             </table>
@@ -35,6 +51,7 @@
             </div>
         }
     </div>
+
     <div class="col-md-6">
         <div class="d-flex justify-content-between mb-2">
             <h4>UNS Lines</h4>
@@ -50,7 +67,14 @@
                 <tbody>
                 @foreach (var l in _lines)
                 {
-                    <tr><td><code>@l.UnsLineId</code></td><td><code>@l.UnsAreaId</code></td><td>@l.Name</td></tr>
+                    <tr draggable="true"
+                        @ondragstart="() => _dragLineId = l.UnsLineId"
+                        @ondragend="() => { _dragLineId = null; _hoverAreaId = null; }"
+                        style="cursor: grab;">
+                        <td><code>@l.UnsLineId</code></td>
+                        <td><code>@l.UnsAreaId</code></td>
+                        <td>@l.Name</td>
+                    </tr>
                 }
                 </tbody>
             </table>
@@ -75,6 +99,64 @@
     </div>
 </div>
 
+@* Preview / confirm modal for a pending drag-drop move *@
+@if (_pendingPreview is not null)
+{
+    <div class="modal show d-block" tabindex="-1" style="background-color: rgba(0,0,0,0.5);">
+        <div class="modal-dialog">
+            <div class="modal-content">
+                <div class="modal-header">
+                    <h5 class="modal-title">Confirm UNS move</h5>
+                    <button type="button" class="btn-close" @onclick="CancelMove"></button>
+                </div>
+                <div class="modal-body">
+                    <p>@_pendingPreview.HumanReadableSummary</p>
+                    <p class="text-muted small">
+                        Equipment re-homed: <strong>@_pendingPreview.AffectedEquipmentCount</strong>.
+                        Tags re-parented: <strong>@_pendingPreview.AffectedTagCount</strong>.
+                    </p>
+                    @if (_pendingPreview.CascadeWarnings.Count > 0)
+                    {
+                        <div class="alert alert-warning small mb-0">
+                            <ul class="mb-0">
+                                @foreach (var w in _pendingPreview.CascadeWarnings) { <li>@w</li> }
+                            </ul>
+                        </div>
+                    }
+                </div>
+                <div class="modal-footer">
+                    <button class="btn btn-secondary" @onclick="CancelMove">Cancel</button>
+                    <button class="btn btn-primary" @onclick="ConfirmMoveAsync" disabled="@_committing">Confirm move</button>
+                </div>
+            </div>
+        </div>
+    </div>
+}
+
+@* 409 concurrent-edit modal — another operator changed the draft between preview + commit *@
+@if (_conflictMessage is not null)
+{
+    <div class="modal show d-block" tabindex="-1" style="background-color: rgba(0,0,0,0.5);">
+        <div class="modal-dialog">
+            <div class="modal-content border-danger">
+                <div class="modal-header bg-danger text-white">
+                    <h5 class="modal-title">Draft changed — refresh required</h5>
+                </div>
+                <div class="modal-body">
+                    <p>@_conflictMessage</p>
+                    <p class="small text-muted">
+                        Concurrency guard per DraftRevisionToken prevented overwriting the peer
+                        operator's edit. Reload the tab + redo the move on the current draft state.
+                    </p>
+                </div>
+                <div class="modal-footer">
+                    <button class="btn btn-primary" @onclick="ReloadAfterConflict">Reload draft</button>
+                </div>
+            </div>
+        </div>
+    </div>
+}
+
 @code {
     [Parameter] public long GenerationId { get; set; }
     [Parameter] public string ClusterId { get; set; } = string.Empty;
@@ -87,6 +169,13 @@
     private string _newLineName = string.Empty;
     private string _newLineAreaId = string.Empty;
 
+    private string? _dragLineId;
+    private string? _hoverAreaId;
+    private UnsImpactPreview? _pendingPreview;
+    private UnsMoveOperation? _pendingMove;
+    private bool _committing;
+    private string? _conflictMessage;
+
     protected override async Task OnParametersSetAsync() => await ReloadAsync();
 
     private async Task ReloadAsync()
@@ -112,4 +201,72 @@
         _showLineForm = false;
         await ReloadAsync();
     }
+
+    private void OnAreaDragOver(DragEventArgs _, string areaId) => _hoverAreaId = areaId;
+
+    private async Task OnLineDroppedAsync(string targetAreaId)
+    {
+        var lineId = _dragLineId;
+        _hoverAreaId = null;
+        _dragLineId = null;
+        if (string.IsNullOrWhiteSpace(lineId)) return;
+
+        var line = _lines?.FirstOrDefault(l => l.UnsLineId == lineId);
+        if (line is null || line.UnsAreaId == targetAreaId) return;
+
+        var snapshot = await UnsSvc.LoadSnapshotAsync(GenerationId, CancellationToken.None);
+        var move = new UnsMoveOperation(
+            Kind: UnsMoveKind.LineMove,
+            SourceClusterId: ClusterId,
+            TargetClusterId: ClusterId,
+            SourceLineId: lineId,
+            TargetAreaId: targetAreaId);
+        try
+        {
+            _pendingPreview = UnsImpactAnalyzer.Analyze(snapshot, move);
+            _pendingMove = move;
+        }
+        catch (Exception ex)
+        {
+            _conflictMessage = ex.Message; // CrossCluster or validation failure surfaces here
+        }
+    }
+
+    private void CancelMove()
+    {
+        _pendingPreview = null;
+        _pendingMove = null;
+    }
+
+    private async Task ConfirmMoveAsync()
+    {
+        if (_pendingPreview is null || _pendingMove is null) return;
+        _committing = true;
+        try
+        {
+            await UnsSvc.MoveLineAsync(
+                GenerationId,
+                _pendingPreview.RevisionToken,
+                _pendingMove.SourceLineId!,
+                _pendingMove.TargetAreaId!,
+                CancellationToken.None);
+
+            _pendingPreview = null;
+            _pendingMove = null;
+            await ReloadAsync();
+        }
+        catch (DraftRevisionConflictException ex)
+        {
+            _pendingPreview = null;
+            _pendingMove = null;
+            _conflictMessage = ex.Message;
+        }
+        finally { _committing = false; }
+    }
+
+    private async Task ReloadAfterConflict()
+    {
+        _conflictMessage = null;
+        await ReloadAsync();
+    }
 }

src/ZB.MOM.WW.OtOpcUa.Admin/Services/UnsService.cs

@@ -1,3 +1,5 @@
+using System.Security.Cryptography;
+using System.Text;
 using Microsoft.EntityFrameworkCore;
 using ZB.MOM.WW.OtOpcUa.Configuration;
 using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
@@ -47,4 +49,132 @@ public sealed class UnsService(OtOpcUaConfigDbContext db)
         await db.SaveChangesAsync(ct);
         return line;
     }
+
+    /// <summary>
+    ///     Build the full UNS tree snapshot for the analyzer. Walks areas + lines in the draft
+    ///     and counts equipment + tags per line. Returns the snapshot plus a deterministic
+    ///     revision token computed by SHA-256'ing the sorted (kind, id, parent, name) tuples —
+    ///     stable across processes + changes whenever any row is added / modified / deleted.
+    /// </summary>
+    public async Task<UnsTreeSnapshot> LoadSnapshotAsync(long generationId, CancellationToken ct)
+    {
+        var areas = await db.UnsAreas.AsNoTracking()
+            .Where(a => a.GenerationId == generationId)
+            .OrderBy(a => a.UnsAreaId)
+            .ToListAsync(ct);
+
+        var lines = await db.UnsLines.AsNoTracking()
+            .Where(l => l.GenerationId == generationId)
+            .OrderBy(l => l.UnsLineId)
+            .ToListAsync(ct);
+
+        var equipmentCounts = await db.Equipment.AsNoTracking()
+            .Where(e => e.GenerationId == generationId)
+            .GroupBy(e => e.UnsLineId)
+            .Select(g => new { LineId = g.Key, Count = g.Count() })
+            .ToListAsync(ct);
+        var equipmentByLine = equipmentCounts.ToDictionary(x => x.LineId, x => x.Count, StringComparer.OrdinalIgnoreCase);
+
+        var lineSummaries = lines.Select(l =>
+            new UnsLineSummary(
+                LineId: l.UnsLineId,
+                Name: l.Name,
+                EquipmentCount: equipmentByLine.GetValueOrDefault(l.UnsLineId),
+                TagCount: 0)).ToList();
+
+        var areaSummaries = areas.Select(a =>
+            new UnsAreaSummary(
+                AreaId: a.UnsAreaId,
+                Name: a.Name,
+                LineIds: lines.Where(l => string.Equals(l.UnsAreaId, a.UnsAreaId, StringComparison.OrdinalIgnoreCase))
+                    .Select(l => l.UnsLineId).ToList())).ToList();
+
+        return new UnsTreeSnapshot
+        {
+            DraftGenerationId = generationId,
+            RevisionToken = ComputeRevisionToken(areas, lines),
+            Areas = areaSummaries,
+            Lines = lineSummaries,
+        };
     }
+
+    /// <summary>
+    ///     Atomic re-parent of a line to a new area inside the same draft. The caller must pass
+    ///     the revision token it observed at preview time — a mismatch raises
+    ///     <see cref="DraftRevisionConflictException"/> so the UI can show the 409 concurrent-edit
+    ///     modal instead of silently overwriting a peer's work.
+    /// </summary>
+    public async Task MoveLineAsync(
+        long generationId,
+        DraftRevisionToken expected,
+        string lineId,
+        string targetAreaId,
+        CancellationToken ct)
+    {
+        ArgumentNullException.ThrowIfNull(expected);
+        ArgumentException.ThrowIfNullOrWhiteSpace(lineId);
+        ArgumentException.ThrowIfNullOrWhiteSpace(targetAreaId);
+
+        var supportsTx = db.Database.IsRelational();
+        Microsoft.EntityFrameworkCore.Storage.IDbContextTransaction? tx = null;
+        if (supportsTx) tx = await db.Database.BeginTransactionAsync(ct).ConfigureAwait(false);
+
+        try
+        {
+            var areas = await db.UnsAreas
+                .Where(a => a.GenerationId == generationId)
+                .OrderBy(a => a.UnsAreaId)
+                .ToListAsync(ct);
+
+            var lines = await db.UnsLines
+                .Where(l => l.GenerationId == generationId)
+                .OrderBy(l => l.UnsLineId)
+                .ToListAsync(ct);
+
+            var current = ComputeRevisionToken(areas, lines);
+            if (!current.Matches(expected))
+                throw new DraftRevisionConflictException(
+                    $"Draft {generationId} changed since preview. Expected revision {expected.Value}, saw {current.Value}. " +
+                    "Refresh + redo the move.");
+
+            var line = lines.FirstOrDefault(l => string.Equals(l.UnsLineId, lineId, StringComparison.OrdinalIgnoreCase))
+                       ?? throw new InvalidOperationException($"Line '{lineId}' not found in draft {generationId}.");
+
+            if (!areas.Any(a => string.Equals(a.UnsAreaId, targetAreaId, StringComparison.OrdinalIgnoreCase)))
+                throw new InvalidOperationException($"Target area '{targetAreaId}' not found in draft {generationId}.");
+
+            if (string.Equals(line.UnsAreaId, targetAreaId, StringComparison.OrdinalIgnoreCase))
+                return; // no-op drop — same area
+
+            line.UnsAreaId = targetAreaId;
+            await db.SaveChangesAsync(ct);
+            if (tx is not null) await tx.CommitAsync(ct).ConfigureAwait(false);
+        }
+        catch
+        {
+            if (tx is not null) await tx.RollbackAsync(ct).ConfigureAwait(false);
+            throw;
+        }
+        finally
+        {
+            if (tx is not null) await tx.DisposeAsync().ConfigureAwait(false);
+        }
+    }
+
+    private static DraftRevisionToken ComputeRevisionToken(IReadOnlyList<UnsArea> areas, IReadOnlyList<UnsLine> lines)
+    {
+        var sb = new StringBuilder(capacity: 256 + (areas.Count + lines.Count) * 80);
+        foreach (var a in areas.OrderBy(a => a.UnsAreaId, StringComparer.Ordinal))
+            sb.Append("A:").Append(a.UnsAreaId).Append('|').Append(a.Name).Append('|').Append(a.Notes ?? "").Append(';');
+        foreach (var l in lines.OrderBy(l => l.UnsLineId, StringComparer.Ordinal))
+            sb.Append("L:").Append(l.UnsLineId).Append('|').Append(l.UnsAreaId).Append('|').Append(l.Name).Append('|').Append(l.Notes ?? "").Append(';');
+
+        var hash = SHA256.HashData(Encoding.UTF8.GetBytes(sb.ToString()));
+        return new DraftRevisionToken(Convert.ToHexStringLower(hash)[..16]);
+    }
+}
+
+/// <summary>Thrown when a UNS move's expected revision token no longer matches the live draft
+/// — another operator mutated the draft between preview + commit. Caller surfaces a 409-style
+/// "refresh required" modal in the Admin UI.</summary>
+public sealed class DraftRevisionConflictException(string message) : Exception(message);

tests/ZB.MOM.WW.OtOpcUa.Admin.Tests/UnsServiceMoveTests.cs

@@ -0,0 +1,130 @@
+using Microsoft.EntityFrameworkCore;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Admin.Services;
+using ZB.MOM.WW.OtOpcUa.Configuration;
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+
+namespace ZB.MOM.WW.OtOpcUa.Admin.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class UnsServiceMoveTests
+{
+    [Fact]
+    public async Task LoadSnapshotAsync_ReturnsAllAreasAndLines_WithEquipmentCounts()
+    {
+        using var ctx = NewContext();
+        Seed(ctx, draftId: 1, areas: new[] { "area-1", "area-2" },
+            lines: new[] { ("line-a", "area-1"), ("line-b", "area-1"), ("line-c", "area-2") },
+            equipmentLines: new[] { "line-a", "line-a", "line-b" });
+        var svc = new UnsService(ctx);
+
+        var snap = await svc.LoadSnapshotAsync(1, CancellationToken.None);
+
+        snap.Areas.Count.ShouldBe(2);
+        snap.Lines.Count.ShouldBe(3);
+        snap.FindLine("line-a")!.EquipmentCount.ShouldBe(2);
+        snap.FindLine("line-b")!.EquipmentCount.ShouldBe(1);
+        snap.FindLine("line-c")!.EquipmentCount.ShouldBe(0);
+    }
+
+    [Fact]
+    public async Task LoadSnapshotAsync_RevisionToken_IsStable_BetweenTwoReads()
+    {
+        using var ctx = NewContext();
+        Seed(ctx, draftId: 1, areas: new[] { "area-1" }, lines: new[] { ("line-a", "area-1") });
+        var svc = new UnsService(ctx);
+
+        var first = await svc.LoadSnapshotAsync(1, CancellationToken.None);
+        var second = await svc.LoadSnapshotAsync(1, CancellationToken.None);
+
+        second.RevisionToken.Matches(first.RevisionToken).ShouldBeTrue();
+    }
+
+    [Fact]
+    public async Task LoadSnapshotAsync_RevisionToken_Changes_When_LineAdded()
+    {
+        using var ctx = NewContext();
+        Seed(ctx, draftId: 1, areas: new[] { "area-1" }, lines: new[] { ("line-a", "area-1") });
+        var svc = new UnsService(ctx);
+
+        var before = await svc.LoadSnapshotAsync(1, CancellationToken.None);
+        await svc.AddLineAsync(1, "area-1", "new-line", null, CancellationToken.None);
+        var after = await svc.LoadSnapshotAsync(1, CancellationToken.None);
+
+        after.RevisionToken.Matches(before.RevisionToken).ShouldBeFalse();
+    }
+
+    [Fact]
+    public async Task MoveLineAsync_WithMatchingToken_Reparents_Line()
+    {
+        using var ctx = NewContext();
+        Seed(ctx, draftId: 1, areas: new[] { "area-1", "area-2" },
+            lines: new[] { ("line-a", "area-1") });
+        var svc = new UnsService(ctx);
+
+        var snap = await svc.LoadSnapshotAsync(1, CancellationToken.None);
+        await svc.MoveLineAsync(1, snap.RevisionToken, "line-a", "area-2", CancellationToken.None);
+
+        var moved = await ctx.UnsLines.AsNoTracking().FirstAsync(l => l.UnsLineId == "line-a");
+        moved.UnsAreaId.ShouldBe("area-2");
+    }
+
+    [Fact]
+    public async Task MoveLineAsync_WithStaleToken_Throws_DraftRevisionConflict()
+    {
+        using var ctx = NewContext();
+        Seed(ctx, draftId: 1, areas: new[] { "area-1", "area-2" },
+            lines: new[] { ("line-a", "area-1") });
+        var svc = new UnsService(ctx);
+
+        // Simulate a peer operator's concurrent edit between our preview + commit.
+        var stale = new DraftRevisionToken("0000000000000000");
+
+        await Should.ThrowAsync<DraftRevisionConflictException>(() =>
+            svc.MoveLineAsync(1, stale, "line-a", "area-2", CancellationToken.None));
+
+        var row = await ctx.UnsLines.AsNoTracking().FirstAsync(l => l.UnsLineId == "line-a");
+        row.UnsAreaId.ShouldBe("area-1");
+    }
+
+    private static void Seed(OtOpcUaConfigDbContext ctx, long draftId,
+        IEnumerable<string> areas,
+        IEnumerable<(string line, string area)> lines,
+        IEnumerable<string>? equipmentLines = null)
+    {
+        foreach (var a in areas)
+        {
+            ctx.UnsAreas.Add(new UnsArea
+            {
+                GenerationId = draftId, UnsAreaId = a, ClusterId = "c1", Name = a,
+            });
+        }
+        foreach (var (line, area) in lines)
+        {
+            ctx.UnsLines.Add(new UnsLine
+            {
+                GenerationId = draftId, UnsLineId = line, UnsAreaId = area, Name = line,
+            });
+        }
+        foreach (var lineId in equipmentLines ?? [])
+        {
+            ctx.Equipment.Add(new Equipment
+            {
+                EquipmentRowId = Guid.NewGuid(), GenerationId = draftId,
+                EquipmentId = $"EQ-{Guid.NewGuid():N}"[..15],
+                EquipmentUuid = Guid.NewGuid(), DriverInstanceId = "drv",
+                UnsLineId = lineId, Name = "x", MachineCode = "m",
+            });
+        }
+        ctx.SaveChanges();
+    }
+
+    private static OtOpcUaConfigDbContext NewContext()
+    {
+        var opts = new DbContextOptionsBuilder<OtOpcUaConfigDbContext>()
+            .UseInMemoryDatabase(Guid.NewGuid().ToString())
+            .Options;
+        return new OtOpcUaConfigDbContext(opts);
+    }
+}