Auto: twincat-4.1 — nested UDT browse via online type walker

Closes #315

tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.IntegrationTests/TwinCatProject/README.md

@@ -198,6 +198,45 @@ Options to eliminate the manual step:
   the rotation permanently, worth it if the integration host is
   long-lived.
 
+## Complex hierarchy
+
+PR 4.1 / #315 (nested-UDT browse via online type walker) exercises
+`TwinCATTypeWalker.Walk` against a real PLC symbol graph. The fixture
+state required:
+
+### DUTs
+
+- `PLC/DUTs/ST_NestedFlags.TcDUT` — mixed-atomic struct (BOOL / INT / REAL /
+  STRING) used for the per-member flatten coverage.
+- `PLC/DUTs/ST_AlarmRecord.TcDUT` — small two-field struct used as the
+  element type of the cutoff array.
+- `PLC/DUTs/ST_RecursiveCap.TcDUT` — struct with a `POINTER TO`
+  self-reference; verifies the walker's pointer-skip + cycle-guard
+  paths terminate without exploding the symbol stream.
+
+### GVL: `GVL_Plant`
+
+```st
+VAR_GLOBAL
+    stFlags        : ST_NestedFlags;
+    aAlarmRecords  : ARRAY[1..2000] OF ST_AlarmRecord;
+END_VAR
+```
+
+`stFlags` produces N atomic leaves where N = the number of `ST_NestedFlags`
+fields. `aAlarmRecords` has 2000 elements which exceeds the default
+`TwinCATDriverOptions.MaxArrayExpansion` (1024) — discovery surfaces it as
+a single `IsArrayRoot` leaf rather than 4000 per-element rows. Lower the
+cap on the driver instance to force per-element expansion (or raise it if
+the operator wants the per-element view).
+
+The XAE-form artefacts ship at `PLC/DUTs/*.TcDUT` + `PLC/GVLs/GVL_Plant.TcGVL`;
+import them into the PLC project alongside `GVL_Fixture` + `GVL_Perf`.
+
+The integration test that exercises this fixture lives at
+`tests/.../TwinCATUdtBrowseTests.cs` and skips via `[TwinCATFact]` when
+the XAR runtime isn't reachable.
+
 ## Online-change test scenario
 
 PR 2.3 (proactive Symbol-Version invalidation listener) ships an