fix(focas): a missing O-number or refused program sub-read goes Bad, not a Good 0

WireFocasClient.GetProgramInfoAsync defaulted every field the CNC did not report:
ONumber ?? 0 when the cnc_exeprgname2 payload was too short to carry it, and
Name '' / BlockCount 0 / Mode 0 when the sub-read was refused. 0 is a genuine
O-number (a 31i reports 0 for a path-executed program -- live Z-34184), a
genuine block count, and Mode 0 is MDI, a real operating mode.

FocasProgramInfo fields are now nullable; MapProgramInfo leaves unreported
fields null and the fixed tree publishes them BadNoData while the bundle's
other fields stay Good.

Ported from the sister ignitionoee FOCAS driver (101a3b1, 2026-08-12).

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDriver.cs

@@ -1307,8 +1307,8 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
                 "Program/MainNumber" => state.LastProgramAxisRef?.MainProgramNumber,
                 "Program/Sequence" => state.LastProgramAxisRef?.SequenceNumber,
                 "OperationMode/Mode" => state.LastProgramInfo?.Mode,
-                "OperationMode/ModeText" => state.LastProgramInfo is { } pi
-                    ? FocasOpMode.ToText(pi.Mode) : null,
+                "OperationMode/ModeText" => state.LastProgramInfo?.Mode is { } mode
+                    ? FocasOpMode.ToText(mode) : null,
                 "Timers/PowerOnSeconds" => TimerValue(state, FocasTimerKind.PowerOn),
                 "Timers/OperatingSeconds" => TimerValue(state, FocasTimerKind.Operating),
                 "Timers/CuttingSeconds" => TimerValue(state, FocasTimerKind.Cutting),
@@ -1317,6 +1317,18 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
             };
             if (value is not null)
                 return new DataValueSnapshot(value, status, sourceUtc, now);
+
+            // The program bundle has been read, but the CNC did not report this field (a refused
+            // sub-read, or no O-number in the payload). That is Bad — never a fabricated 0, and
+            // not "no such node" either.
+            if (state.LastProgramInfo is not null
+                && path is "Program/Name" or "Program/ONumber" or "Program/BlockCount"
+                    or "OperationMode/Mode" or "OperationMode/ModeText")
+                return new DataValueSnapshot(
+                    null,
+                    status == FocasStatusMapper.Good ? FocasStatusMapper.BadNoData : status,
+                    sourceUtc,
+                    now);
         }
         return null;
     }

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/IFocasClient.cs

@@ -238,12 +238,15 @@ public sealed record FocasSpindleName(string Name, string Suffix1, string Suffix
 ///     Program + operation-mode snapshot. Name is the currently-executing
 ///     program filename (e.g. "O0001.NC"); ONumber is its Fanuc O-number (1-9999).
 ///     Mode is the numeric code from <c>cnc_rdopmode</c> — see <see cref="FocasOpMode"/>.
+///     <b>A null field means the CNC did not report it</b> (its sub-read was refused, or the
+///     payload was too short to carry it); the driver publishes that node Bad. It is never
+///     defaulted to <c>0</c>, which is a genuine O-number, block count, and mode (MDI).
 /// </summary>
 public sealed record FocasProgramInfo(
-    string Name,
-    int ONumber,
-    int BlockCount,
-    int Mode);
+    string? Name,
+    int? ONumber,
+    int? BlockCount,
+    int? Mode);
 
 /// <summary>Human-readable text for the <see cref="FocasProgramInfo.Mode"/> integer.</summary>
 public static class FocasOpMode

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/Wire/WireFocasClient.cs

@@ -217,12 +217,29 @@ public sealed class WireFocasClient : IFocasClient
             throw new InvalidOperationException(
                 $"cnc_exeprgname2 failed EW_{nameResult.Rc} and cnc_rdopmode failed EW_{modeResult.Rc}.");
 
-        var wireName = nameResult.Value;
+        return MapProgramInfo(nameResult, blkResult, modeResult);
+    }
+
+    /// <summary>
+    ///     Combine the three program sub-reads into a <see cref="FocasProgramInfo"/>, leaving any
+    ///     field the CNC did not report null. A refused read, or an <c>cnc_exeprgname2</c> payload
+    ///     too short to carry the trailing O-number, used to publish a fabricated <c>0</c> at Good
+    ///     quality — indistinguishable from a real 0 (a 31i reports O-number 0 for a program run
+    ///     by path) and, for the mode, from MDI. Ported from the sister ignitionoee driver (101a3b1).
+    /// </summary>
+    /// <param name="name">The <c>cnc_exeprgname2</c> result.</param>
+    /// <param name="blockCount">The <c>cnc_rdblkcount</c> result.</param>
+    /// <param name="mode">The <c>cnc_rdopmode</c> result.</param>
+    /// <returns>The snapshot, null where the CNC did not say.</returns>
+    internal static FocasProgramInfo MapProgramInfo(
+        FocasResult<WireProgramName> name, FocasResult<int> blockCount, FocasResult<short> mode)
+    {
+        var wireName = name.IsOk ? name.Value : null;
         return new FocasProgramInfo(
-            Name: wireName?.Name ?? string.Empty,
-            ONumber: wireName?.ONumber ?? 0,
-            BlockCount: blkResult.IsOk ? blkResult.Value : 0,
-            Mode: modeResult.IsOk ? modeResult.Value : 0);
+            Name: wireName?.Name,
+            ONumber: wireName?.ONumber,
+            BlockCount: blockCount.IsOk ? blockCount.Value : null,
+            Mode: mode.IsOk ? mode.Value : null);
     }
 
     /// <inheritdoc />