fix(driver-twincat): resolve Medium code-review finding (Driver.TwinCAT-010)

Replace yield break with cancellationToken.ThrowIfCancellationRequested()
in BrowseSymbolsAsync so a cancelled browse propagates as
OperationCanceledException instead of silently completing with a partial
symbol set.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

code-reviews/Driver.TwinCAT/findings.md

@@ -272,7 +272,7 @@ symbol set with no indication it was truncated. The `SymbolLoaderFactory.Create`
 `yield break` so a cancelled browse surfaces as cancellation, not as a successful but partial
 discovery.
 
-**Resolution:** _(open)_
+**Resolution:** Resolved 2026-05-22 — replaced `yield break` with `cancellationToken.ThrowIfCancellationRequested()` in the `foreach` loop so a cancelled browse propagates as `OperationCanceledException`, matching the `DiscoverAsync` expectation.
 
 ### Driver.TwinCAT-011
 

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/AdsTwinCATClient.cs

@@ -244,7 +244,12 @@ internal sealed class AdsTwinCATClient : ITwinCATClient
 
         foreach (ISymbol symbol in loader.Symbols)
         {
-            if (cancellationToken.IsCancellationRequested) yield break;
+            // ThrowIfCancellationRequested — not yield break — so a cancelled browse propagates
+            // as OperationCanceledException rather than a silent clean completion. DiscoverAsync
+            // has an explicit catch(OperationCanceledException){ throw; } to surface this
+            // distinctly from a genuine browse failure; a yield break would let a partial
+            // symbol set appear as a fully successful discovery (Driver.TwinCAT-010).
+            cancellationToken.ThrowIfCancellationRequested();
             var mapped = MapSymbolTypeName(symbol.DataType?.Name);
             var readOnly = !IsSymbolWritable(symbol);
             yield return new TwinCATDiscoveredSymbol(symbol.InstancePath, mapped, readOnly);