feat(hosts): driver diagnostics channel on /hosts, S7 negotiated PDU size first (#640)

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Pages/Hosts.razor

@@ -189,6 +189,17 @@ else
                                                 @* Own line — inline after the name the two identifiers ran together. *@
                                                 <div class="mono small text-muted">@d.DriverInstanceId</div>
                                             }
+                                            @if (d.DiagnosticItems.Count > 0)
+                                            {
+                                                @* Driver-reported diagnostics (Gitea #640), e.g. S7 negotiated PDU size.
+                                                   Renders nothing for a driver with none. *@
+                                                <div class="small text-muted" data-testid="driver-diagnostics">
+                                                    @foreach (var kv in d.DiagnosticItems)
+                                                    {
+                                                        <div class="mono">@kv.Key: @kv.Value</div>
+                                                    }
+                                                </div>
+                                            }
                                         </td>
                                         <td>@(d.DriverType ?? "—")</td>
                                         <td><span class="chip @DriverChipClass(d.State)">@d.State</span></td>

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Hosts/HostsDriverView.cs

@@ -52,6 +52,8 @@ public sealed record HostsDriverInstanceInfo(
 ///     is no answer — the driver cannot report skips, or it faulted before building a tag table. Lets
 ///     "ignoring 20 of 22 tags" show even while every other column on the row — state, last read, error
 ///     count, last error — reads perfectly healthy (Gitea #541).</param>
+/// <param name="Diagnostics">Driver-reported diagnostics (e.g. S7 negotiated PDU size); null or empty when
+///     the driver has none to show (Gitea #640).</param>
 /// <param name="Enabled">Whether the matching configured instance is authored enabled; <see langword="true"/>
 ///     when no instance matched. Fed to the row's expandable <c>DriverStatusPanel</c> (Gitea #546). An
 ///     unmatched row defaults to enabled on purpose: the row only exists because a live snapshot arrived,
@@ -62,8 +64,16 @@ public sealed record HostsDriverRow(
     DateTime? RediscoveryNeededUtc = null, string? RediscoveryReason = null,
     IReadOnlyList<HostConnectivityStatus>? HostStatuses = null,
     SkippedTagReport? SkippedTags = null,
-    bool Enabled = true)
+    bool Enabled = true,
+    IReadOnlyDictionary<string, string>? Diagnostics = null)
 {
+    /// <summary>Diagnostics as ordered key/value pairs for rendering; empty when there are none, in which
+    /// case the page renders nothing.</summary>
+    public IReadOnlyList<KeyValuePair<string, string>> DiagnosticItems { get; } =
+        (Diagnostics ?? new Dictionary<string, string>())
+            .OrderBy(k => k.Key, StringComparer.Ordinal)
+            .ToList();
+
     /// <summary>Whether this driver is ignoring at least one authored tag — the condition the whole
     /// column exists to make visible.</summary>
     public bool HasSkippedTags => SkippedTags is { SkippedCount: > 0 };
@@ -177,7 +187,8 @@ public static class HostsDriverView
                         s.RediscoveryReason,
                         s.HostStatuses,
                         s.SkippedTags,
-                        instance?.Enabled ?? true);
+                        instance?.Enabled ?? true,
+                        s.Diagnostics);
                 })
                 .OrderBy(d => d.Name ?? d.DriverInstanceId, StringComparer.OrdinalIgnoreCase)
                 .ThenBy(d => d.DriverInstanceId, StringComparer.OrdinalIgnoreCase)