Auto: s7-d2 — UDT / STRUCT / nested-DB fan-out

Closes #300

src/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs

@@ -2,6 +2,7 @@ using System.Buffers.Binary;
 using System.Collections.Generic;
 using S7.Net;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.S7.SymbolImport;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.S7;
 
@@ -67,6 +68,14 @@ public sealed class S7Driver(S7DriverOptions options, string driverInstanceId)
     private readonly Dictionary<string, S7TagDefinition> _tagsByName = new(StringComparer.OrdinalIgnoreCase);
     private readonly Dictionary<string, S7ParsedAddress> _parsedByName = new(StringComparer.OrdinalIgnoreCase);
 
+    /// <summary>
+    ///     PR-S7-D2 — post-fan-out tag list, in declaration order. Mirrors
+    ///     <see cref="_tagsByName"/> as a list so <see cref="DiscoverAsync"/> can produce a
+    ///     stable browse-tree ordering. Always preserves the original declaration order;
+    ///     UDT tags are replaced in-place by their fanned-out leaf children.
+    /// </summary>
+    private readonly List<S7TagDefinition> _effectiveTags = new();
+
     private readonly S7DriverOptions _options = options;
     private readonly SemaphoreSlim _gate = new(1, 1);
 
@@ -141,8 +150,39 @@ public sealed class S7Driver(S7DriverOptions options, string driverInstanceId)
             // story this lets the Admin UI's "Save" round-trip stay sub-second on bad input.
             _tagsByName.Clear();
             _parsedByName.Clear();
+            _effectiveTags.Clear();
             foreach (var t in _options.Tags)
             {
+                // PR-S7-D2 — UDT-typed tags are fanned out into N scalar leaf member tags
+                // before any address parsing happens against the parent. Reads / writes /
+                // subscribes never see the parent UDT tag; only its scalar children.
+                if (!string.IsNullOrWhiteSpace(t.UdtName))
+                {
+                    if (t.ElementCount is int udtElems && udtElems > 1)
+                        throw new FormatException(
+                            $"S7 tag '{t.Name}' is UDT-typed (UdtName='{t.UdtName}') and ElementCount > 1; " +
+                            "array-of-UDT must be expressed via array members inside the UDT layout, " +
+                            "not at the parent-tag level");
+
+                    // Parse the parent-tag base address once so the fan-out can compute
+                    // member byte offsets relative to ByteOffset. Parser uses CpuType for
+                    // V-memory mapping on S7-200 / LOGO families.
+                    var parentParsed = S7AddressParser.Parse(t.Address, _options.CpuType);
+                    var leaves = S7UdtFanOut.Expand(t, _options.Udts, parentParsed);
+                    foreach (var leaf in leaves)
+                    {
+                        var leafParsed = S7AddressParser.Parse(leaf.Address, _options.CpuType);
+                        if (_tagsByName.ContainsKey(leaf.Name))
+                            throw new InvalidOperationException(
+                                $"S7 tag '{leaf.Name}' (fanned out from UDT '{t.UdtName}' on tag '{t.Name}') " +
+                                "collides with an existing tag name");
+                        _tagsByName[leaf.Name] = leaf;
+                        _parsedByName[leaf.Name] = leafParsed;
+                        _effectiveTags.Add(leaf);
+                    }
+                    continue;
+                }
+
                 // Pass CpuType so V-memory addresses (S7-200 / S7-200 Smart / LOGO!) resolve
                 // against the device's family-specific DB mapping.
                 var parsed = S7AddressParser.Parse(t.Address, _options.CpuType); // throws FormatException
@@ -161,6 +201,7 @@ public sealed class S7Driver(S7DriverOptions options, string driverInstanceId)
                 }
                 _tagsByName[t.Name] = t;
                 _parsedByName[t.Name] = parsed;
+                _effectiveTags.Add(t);
             }
 
             var plc = BuildPlc();
@@ -244,6 +285,9 @@ public sealed class S7Driver(S7DriverOptions options, string driverInstanceId)
         // Reset the snapshot so a post-shutdown diagnostics read doesn't display a stale
         // PDU size from the previous connection. Reinit will repopulate after OpenAsync.
         _negotiatedPduSize = 0;
+        // PR-S7-D2 — drop the post-fan-out tag list so a Reinit can rebuild it cleanly
+        // without the previous run's UDT leaves leaking into the new tag map.
+        _effectiveTags.Clear();
         _health = new DriverHealth(DriverState.Unknown, _health.LastSuccessfulRead, null);
         return Task.CompletedTask;
     }
@@ -1019,7 +1063,11 @@ public sealed class S7Driver(S7DriverOptions options, string driverInstanceId)
     {
         ArgumentNullException.ThrowIfNull(builder);
         var folder = builder.Folder("S7", "S7");
-        foreach (var t in _options.Tags)
+        // PR-S7-D2 — iterate the post-fan-out effective tag list so UDT leaves surface as
+        // browseable variables and the original parent UDT tag (which is no longer in the
+        // read/write pipeline) never appears in the address space.
+        var sourceTags = _effectiveTags.Count > 0 ? (IEnumerable<S7TagDefinition>)_effectiveTags : _options.Tags;
+        foreach (var t in sourceTags)
         {
             var isArr = t.ElementCount is int ec && ec > 1;
             folder.Variable(t.Name, t.Name, new DriverAttributeInfo(