fix(abcip): an unknown tag no longer throttles its whole device or reads as a comms error

Live read-only check against a production CompactLogix press: with one nonexistent tag
first in the read list, libplctag's create threw LibPlcTagException("ErrorNotFound"); the
driver counted it as a failed Forward-Open, opened the device's 05/STAB-8 connect-backoff
window, and every other cold tag on the device - all real (WW_InCycle, WW_ActualPress,
WW_WorkOrderNum) - read BadCommunicationError. In steady polling the bad tag re-opens
the window each attempt, so siblings ordered after it may never connect.

- A create that fails with a "controller answered" status (NotFound/NoMatch/BadDevice,
  the probe's existing reachable classification) records backoff SUCCESS, not failure.
  Genuine connection failures still open the window (falsification control test).
- Read exceptions map through the libplctag Status they carry: unknown tag ->
  BadNodeIdUnknown, decode past the buffer -> BadOutOfRange, timeout -> BadTimeout,
  instead of a blanket BadCommunicationError. One status-name parser
  (AbCipStatusMapper.TryGetStatus) now serves both the read path and the probe.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipDriver.cs

@@ -1,3 +1,4 @@
+using libplctag;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
 using ZB.MOM.WW.OtOpcUa.Commons.Observability;
@@ -818,10 +819,12 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
         }
         catch (Exception ex)
         {
-            // Transport exception — evict so the next read creates a fresh handle.
+            // Transport exception — evict so the next read creates a fresh handle. A libplctag
+            // exception carries its Status, so a tag the controller does not have reads
+            // BadNodeIdUnknown and a decode past the buffer BadOutOfRange, not a comms error.
             EvictRuntime(device, def.Name);
             results[fb.OriginalIndex] = new DataValueSnapshot(null,
-                AbCipStatusMapper.BadCommunicationError, null, now);
+                AbCipStatusMapper.MapException(ex), null, now);
             _logger.LogWarning(ex,
                 "AbCip read transport exception for tag {Tag} on device {Device}",
                 reference, def.DeviceHostAddress);
@@ -891,7 +894,7 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
         catch (Exception ex)
         {
             EvictRuntime(device, parent.Name);
-            StampGroupStatus(group, results, now, AbCipStatusMapper.BadCommunicationError);
+            StampGroupStatus(group, results, now, AbCipStatusMapper.MapException(ex));
             _logger.LogWarning(ex,
                 "AbCip whole-UDT read transport exception for parent {Parent} on device {Device}",
                 group.ParentName, parent.DeviceHostAddress);
@@ -1158,10 +1161,20 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
             {
                 await runtime.InitializeAsync(ct).ConfigureAwait(false);
             }
-            catch
+            catch (Exception ex)
             {
                 runtime.Dispose();
-                device.Backoff.RecordFailure(DateTime.UtcNow); // 05/STAB-8: open the backoff window
+                // 05/STAB-8: a failed create opens the backoff window — but only when the device did
+                // not answer. "Tag not found" means the controller replied over a working session; it
+                // is a config error on this one tag, and counting it as a failed Forward-Open throttled
+                // every sibling tag on the device (seen live: one typo blacked out the whole device).
+                if (ex is LibPlcTagException lpe
+                    && AbCipStatusMapper.TryGetStatus(lpe, out var status)
+                    && status != Status.Ok
+                    && AbCipDriverProbe.IsReachableStatus(status))
+                    device.Backoff.RecordSuccess();
+                else
+                    device.Backoff.RecordFailure(DateTime.UtcNow);
                 throw;
             }
             device.Backoff.RecordSuccess(); // 05/STAB-8: Forward-Open succeeded — reset the window

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipDriverProbe.cs

@@ -200,7 +200,7 @@ public sealed class AbCipDriverProbe : IDriverProbe
     internal static bool IsReachableException(LibPlcTagException ex)
     {
         var msg = ex.Message ?? string.Empty;
-        if (Enum.TryParse<Status>(msg.Trim(), ignoreCase: true, out var status) && Enum.IsDefined(status))
+        if (AbCipStatusMapper.TryGetStatus(ex, out var status))
             return IsReachableStatus(status);
 
         return msg.Contains("NOT_FOUND", StringComparison.OrdinalIgnoreCase)

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipStatusMapper.cs

@@ -76,6 +76,34 @@ public static class AbCipStatusMapper
     /// <returns>The mapped OPC UA StatusCode value.</returns>
     public static uint MapLibplctagStatus(int status) => MapLibplctagStatus((Status)status);
 
+    /// <summary>
+    ///     Recover the libplctag <see cref="Status"/> a <see cref="LibPlcTagException"/> was thrown on.
+    ///     The wrapper builds the exception from <c>Status.ToString()</c>, so the message is the enum
+    ///     name (<c>"ErrorNotFound"</c>).
+    /// </summary>
+    /// <param name="ex">The exception.</param>
+    /// <param name="status">The recovered status.</param>
+    /// <returns><c>true</c> when the message names a defined <see cref="Status"/>.</returns>
+    public static bool TryGetStatus(LibPlcTagException ex, out Status status)
+    {
+        ArgumentNullException.ThrowIfNull(ex);
+        return Enum.TryParse((ex.Message ?? string.Empty).Trim(), ignoreCase: true, out status)
+               && Enum.IsDefined(status);
+    }
+
+    /// <summary>
+    ///     Status for an exception thrown while creating / reading a tag: a libplctag exception maps
+    ///     through its <see cref="Status"/> (so a tag the controller does not have reads
+    ///     <see cref="BadNodeIdUnknown"/>, not a comms error); anything else is
+    ///     <see cref="BadCommunicationError"/>.
+    /// </summary>
+    /// <param name="ex">The exception.</param>
+    /// <returns>The OPC UA status code.</returns>
+    public static uint MapException(Exception ex) =>
+        ex is LibPlcTagException lpe && TryGetStatus(lpe, out var status)
+            ? MapLibplctagStatus(status)
+            : BadCommunicationError;
+
     /// <summary>
     ///     Map a libplctag.NET <see cref="Status"/> enum value to an OPC UA StatusCode. This is
     ///     the strongly-typed core of the mapper; the <c>int</c> overload exists only for the