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)

src/Server/ZB.MOM.WW.OtOpcUa.ControlPlane/Telemetry/TelemetryProtoMapCentral.cs

@@ -130,7 +130,8 @@ public static class TelemetryProtoMapCentral
             RediscoveryNeededUtc: msg.RediscoveryNeededUtc?.ToDateTime(),
             RediscoveryReason: msg.HasRediscoveryReason ? msg.RediscoveryReason : null,
             HostStatuses: ToHostStatuses(msg),
-            SkippedTags: ToSkippedTags(msg));
+            SkippedTags: ToSkippedTags(msg),
+            Diagnostics: msg.HasDiagnostics ? new Dictionary<string, string>(msg.Diagnostics) : null);
     }
 
     /// <summary>

src/Server/ZB.MOM.WW.OtOpcUa.Host/Grpc/TelemetryProtoMapNode.cs

@@ -164,6 +164,14 @@ public static class TelemetryProtoMapNode
             msg.SkippedTags = payload;
         }
 
+        // Gitea #640. Presence flag first - an empty map cannot say whether the driver has the capability.
+        if (e.Diagnostics is not null)
+        {
+            msg.HasDiagnostics = true;
+            foreach (var kv in e.Diagnostics)
+                msg.Diagnostics[kv.Key ?? ""] = kv.Value ?? "";
+        }
+
         return msg;
     }
 

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/AkkaDriverHealthPublisher.cs

@@ -38,7 +38,8 @@ public sealed class AkkaDriverHealthPublisher : IDriverHealthPublisher
         DateTime? rediscoveryNeededUtc = null,
         string? rediscoveryReason = null,
         IReadOnlyList<HostConnectivityStatus>? hostStatuses = null,
-        SkippedTagReport? skippedTags = null)
+        SkippedTagReport? skippedTags = null,
+        IReadOnlyDictionary<string, string>? diagnostics = null)
     {
         var msg = new DriverHealthChanged(
             clusterId,
@@ -51,7 +52,8 @@ public sealed class AkkaDriverHealthPublisher : IDriverHealthPublisher
             rediscoveryNeededUtc,
             rediscoveryReason,
             hostStatuses,
-            skippedTags);
+            skippedTags,
+            diagnostics);
         DistributedPubSub.Get(_system).Mediator.Tell(new Publish(TopicName, msg));
         // Phase 5: fan the same snapshot into the node-local live-telemetry hub (no-op until a gRPC
         // client subscribes). The DPS publish above is unchanged — the hub is a strictly additive tap.

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverInstanceActor.cs

@@ -1153,6 +1153,28 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
         }
     }
 
+    /// <summary>Bounded driver diagnostics, or null when the driver is not an <see cref="IDriverDiagnostics"/>
+    /// (Gitea #640). Pulled fresh and called UNGUARDED for the same reasons as
+    /// <see cref="CurrentSkippedTags"/>; a throwing implementation loses only the diagnostics.</summary>
+    private IReadOnlyDictionary<string, string>? CurrentDiagnostics()
+    {
+        if (_driver is not IDriverDiagnostics diag) return null;
+        try
+        {
+            return DriverDiagnostics.Bound(diag.GetDiagnostics());
+        }
+        catch (Exception ex)
+        {
+            _log.Warning(ex, "DriverInstance {Id}: GetDiagnostics threw during health publish; omitting diagnostics", _driverInstanceId);
+            return null;
+        }
+    }
+
+    /// <summary>Value digest of the diagnostics bag for the publish fingerprint. Null in, null out. The bag is
+    /// already in ordinal key order (<see cref="DriverDiagnostics.Bound"/>), so equal facts digest equally.</summary>
+    private static string? DiagnosticsDigest(IReadOnlyDictionary<string, string>? d) =>
+        d is null ? null : string.Join('|', d.Select(kv => $"{kv.Key}={kv.Value}"));
+
     /// <summary>Records the driver's rediscovery raise and re-publishes health so the signal reaches the
     /// AdminUI promptly rather than waiting for the next 30 s heartbeat.
     /// <para><b>Advisory only.</b> The served address space is deliberately NOT rebuilt: v3 authors raw tags
@@ -1357,6 +1379,7 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
             var errorCount = ErrorCount5Min();
             var hostStatuses = CurrentHostStatuses();
             var skippedTags = CurrentSkippedTags();
+            var diagnostics = CurrentDiagnostics();
             // _rediscoveryNeededUtc is PART OF THE FINGERPRINT on purpose. A rediscovery raise on an
             // otherwise-unchanged Healthy driver leaves (state, lastSuccess, lastError, errorCount)
             // identical, so without it the dedup below would swallow the very publish that carries the
@@ -1375,14 +1398,20 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
             // is identical to a clean driver's and the publish that carries the signal is exactly the one
             // dedup would swallow. Flattened to a STRING for the same reason as the host digest — the
             // report holds an IReadOnlyList, which a tuple compares by reference.
+            //
+            // The diagnostics digest (Gitea #640) is the fourth instance: a diagnostic fact (S7's PDU size
+            // changing across a reconnect) moves none of the other components, so without it the publish
+            // that carries it is deduped away. Flattened to a STRING - the bag is a dictionary, which a
+            // tuple compares by reference.
             var fingerprint = (health.State, health.LastSuccessfulRead, health.LastError, errorCount,
-                _rediscoveryNeededUtc, HostStatusDigest(hostStatuses), SkippedTagDigest(skippedTags));
+                _rediscoveryNeededUtc, HostStatusDigest(hostStatuses), SkippedTagDigest(skippedTags),
+                DiagnosticsDigest(diagnostics));
             if (_lastPublishedFingerprint is { } prev && prev.Equals(fingerprint))
                 return observed;
             _lastPublishedFingerprint = fingerprint;
             _healthPublisher.Publish(
                 _clusterId, _driverInstanceId, health, errorCount, _rediscoveryNeededUtc, _rediscoveryReason,
-                hostStatuses, skippedTags);
+                hostStatuses, skippedTags, diagnostics);
         }
         catch (Exception ex)
         {
@@ -1418,7 +1447,8 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
 
     /// <summary>Fingerprint of the last <see cref="PublishHealthSnapshot"/> call; null until first publish.</summary>
     private (DriverState State, DateTime? LastSuccess, string? LastError, int ErrorCount,
-        DateTime? RediscoveryNeededUtc, string? HostStatusDigest, string? SkippedTagDigest)? _lastPublishedFingerprint;
+        DateTime? RediscoveryNeededUtc, string? HostStatusDigest, string? SkippedTagDigest,
+        string? DiagnosticsDigest)? _lastPublishedFingerprint;
 
     /// <inheritdoc />
     protected override void PostStop()