TwinCAT follow-up — Symbol browser via AdsClient + SymbolLoaderFactory. Closes task #188. Adds ITwinCATClient.BrowseSymbolsAsync — IAsyncEnumerable yielding TwinCATDiscoveredSymbol (InstancePath + mapped TwinCATDataType + ReadOnly flag) from the target's flat symbol table. AdsTwinCATClient implementation uses SymbolLoaderFactory.Create(_client, new SymbolLoaderSettings(SymbolsLoadMode.Flat)) + iterates loader.Symbols, maps IEC 61131-3 type names (BOOL/SINT/INT/DINT/LINT/REAL/LREAL/STRING/WSTRING/TIME/DATE/DT/TOD + BYTE/WORD/DWORD/LWORD unsigned-word aliases) through MapSymbolTypeName, checks SymbolAccessRights.Write bit for writable vs read-only. Unsupported types (UDTs / function blocks / arrays / pointers) surface with DataType=null so callers can skip or recurse. TwinCATDriverOptions.EnableControllerBrowse — new bool, default false to preserve the strict-config path. When true, DiscoverAsync iterates each device's BrowseSymbolsAsync, filters via TwinCATSystemSymbolFilter (rejects TwinCAT_*, Constants.*, Mc_*, __*, Global_Version* prefixes + anything empty), skips null-DataType symbols, emits surviving symbols under a per-device Discovered/ sub-folder with InstancePath as both FullName + BrowseName + ReadOnly→ViewOnly/writable→Operate. Pre-declared tags from TwinCATDriverOptions.Tags always emit regardless. Browse failure is non-fatal — exception caught + swallowed, pre-declared tags stay in the address space, operators see the failure in driver health on next read. TwinCATSystemSymbolFilter static class mirrors AbCipSystemTagFilter's shape with TwinCAT-specific prefixes. Fake client updated — BrowseResults list for test setup + FireNotification-style single-invocation on each subscribe, ThrowOnBrowse flag for failure testing. 8 new unit tests — strict path emits only pre-declared when EnableControllerBrowse=false, browse enabled adds Discovered/ folder, filter rejects system prefixes, null-DataType symbols skipped, ReadOnly symbols surface ViewOnly, browse failure leaves pre-declared intact, SystemSymbolFilter theory (10 cases). Total TwinCAT unit tests now 110/110 passing (+17 from the native-notification merge's 93); full solution builds 0 errors; other drivers untouched.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/ITwinCATClient.cs

@@ -66,11 +66,33 @@ public interface ITwinCATClient : IDisposable
         TimeSpan cycleTime,
         Action<string, object?> onChange,
         CancellationToken cancellationToken);
+
+    /// <summary>
+    ///     Walk the target's symbol table via the TwinCAT <c>SymbolLoaderFactory</c> (flat mode).
+    ///     Yields each top-level symbol the PLC exposes — global variables, program-scope locals,
+    ///     function-block instance fields. Filters for our atomic type surface; structured /
+    ///     UDT / function-block typed symbols surface with <c>DataType = null</c> so callers can
+    ///     decide whether to drill in via their own walker.
+    /// </summary>
+    IAsyncEnumerable<TwinCATDiscoveredSymbol> BrowseSymbolsAsync(CancellationToken cancellationToken);
 }
 
 /// <summary>Opaque handle for a registered ADS notification. <see cref="IDisposable.Dispose"/> tears it down.</summary>
 public interface ITwinCATNotificationHandle : IDisposable { }
 
+/// <summary>
+///     One symbol yielded by <see cref="ITwinCATClient.BrowseSymbolsAsync"/> — full instance
+///     path + detected <see cref="TwinCATDataType"/> + read-only flag.
+/// </summary>
+/// <param name="InstancePath">Full dotted symbol path (e.g. <c>MAIN.bStart</c>, <c>GVL.Counter</c>).</param>
+/// <param name="DataType">Mapped <see cref="TwinCATDataType"/>; <c>null</c> when the symbol's type
+///     doesn't map onto our supported atomic surface (UDTs, pointers, function blocks).</param>
+/// <param name="ReadOnly"><c>true</c> when the symbol's AccessRights flag forbids writes.</param>
+public sealed record TwinCATDiscoveredSymbol(
+    string InstancePath,
+    TwinCATDataType? DataType,
+    bool ReadOnly);
+
 /// <summary>Factory for <see cref="ITwinCATClient"/>s. One client per device.</summary>
 public interface ITwinCATClientFactory
 {