fix(central-ui): Debug View picker — disabled-while-connected test; drop no-op handler; static label

Task 5 review follow-ups:

- New DebugViewInstancePickerTests.WhileConnected_ThePickerIsDisabled pins that
  a live connection locks the picker: both the input and the chevron carry
  `disabled`. It marks the page connected by reflection, the way the other
  DebugView page tests do (DebugViewAlarmTableTests) — driving the real gRPC
  stream is not available to a bUnit render.
- OnInstanceSelectionChanged() was already a no-op and its comment described the
  @bind that the picker replaced; deleted, and OnInstancePicked now just records
  the id (XML-documented).
- The ItemLabel lambda is hoisted to a private static InstanceLabel(Instance),
  passed as a method group.

Claude-Session: https://claude.ai/code/session_01NcMG6xXdsJbmD2wYAgkK29

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/DebugView.razor

@@ -83,7 +83,7 @@
             <div class="col-md-4">
                 <label class="form-label small">Instance</label>
                 <InstancePicker Areas="_siteAreas" Instances="_siteInstances"
-                                ItemLabel="@(i => $"{i.UniqueName} ({i.State})")"
+                                ItemLabel="InstanceLabel"
                                 SelectedInstanceId="_selectedInstanceId" SelectedInstanceIdChanged="OnInstancePicked"
                                 Disabled="@_connected" DataTestPrefix="debug-instance" />
             </div>
@@ -455,17 +455,22 @@
         }
     }
 
-    /// <summary>Handles a pick from the <c>InstancePicker</c> combobox.</summary>
+    /// <summary>
-    private void OnInstancePicked(int id)
+    /// The label the <c>InstancePicker</c> renders on a row and in its field:
-    {
+    /// the instance's unique name with its lifecycle state.
-        _selectedInstanceId = id;
+    /// </summary>
-        OnInstanceSelectionChanged();
+    /// <param name="instance">The instance to label.</param>
-    }
+    /// <returns>The display label, e.g. <c>Line1.Mixer (Enabled)</c>.</returns>
+    private static string InstanceLabel(Instance instance) =>
+        $"{instance.UniqueName} ({instance.State})";
 
-    private void OnInstanceSelectionChanged()
+    /// <summary>
-    {
+    /// Records the instance the operator picked in the <c>InstancePicker</c>.
-        // No-op; selection is tracked via _selectedInstanceId binding
+    /// Everything downstream (the Connect button's enablement, <c>Connect()</c>
-    }
+    /// itself) reads <c>_selectedInstanceId</c>, so there is nothing else to do.
+    /// </summary>
+    /// <param name="id">Id of the picked instance.</param>
+    private void OnInstancePicked(int id) => _selectedInstanceId = id;
 
     /// <summary>
     /// When the attribute filter changes, expand the tree so any branches holding

tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/DebugViewInstancePickerTests.cs

@@ -1,3 +1,4 @@
+using System.Reflection;
 using System.Security.Claims;
 using Bunit;
 using Microsoft.AspNetCore.Components.Authorization;
@@ -21,7 +22,8 @@ namespace ZB.MOM.WW.ScadaBridge.CentralUI.Tests.Deployment;
 /// <c>&lt;select&gt;</c> to the shared <c>InstancePicker</c> area-tree combobox
 /// (design 2026-09-08). Pins that the page hands the picker the site's areas and
 /// its Enabled-only instance list, that drilling down the tree selects an instance,
-/// and that the selection still enables <em>Connect</em>.
+/// that the selection still enables <em>Connect</em>, and that a live connection
+/// locks the picker down.
 /// </summary>
 public class DebugViewInstancePickerTests : BunitContext
 {
@@ -153,4 +155,22 @@ public class DebugViewInstancePickerTests : BunitContext
             .First(b => b.TextContent.Contains("Connect"));
         Assert.False(connect.HasAttribute("disabled"));
     }
+
+    [Fact]
+    public void WhileConnected_ThePickerIsDisabled()
+    {
+        RegisterServices();
+        var cut = Render<DebugViewPage>();
+        cut.Find("[data-test='debug-site-select']").Change(SiteId.ToString());
+
+        // Mark the page connected the way the other DebugView page tests do —
+        // driving the real gRPC stream is not available to a bUnit render.
+        cut.InvokeAsync(() => typeof(DebugViewPage)
+            .GetField("_connected", BindingFlags.Instance | BindingFlags.NonPublic)!
+            .SetValue(cut.Instance, true));
+        cut.Render();
+
+        Assert.True(cut.Find("[data-test='debug-instance-input']").HasAttribute("disabled"));
+        Assert.True(cut.Find("[data-test='debug-instance-toggle']").HasAttribute("disabled"));
+    }
 }