Auto: twincat-2.1 — ADS Sum-read / Sum-write

Closes #310

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

@@ -71,6 +71,70 @@ GVL_Fixture.nCounter := GVL_Fixture.nCounter + 1;
 - `PlcTask` — cyclic, 10 ms interval, priority 20
 - Assigned to `MAIN`
 
+## Performance scenarios
+
+PR 2.1 (ADS Sum-read / Sum-write) ships an opt-in perf-tier integration test
+(`TwinCATSumCommandPerfTests.Driver_sum_read_1000_tags_beats_loop_baseline_by_5x`)
+that reads 1000 DINTs in one shot and asserts the bulk path beats the per-tag
+loop by ≥ 5×. The fixture state required by that test is:
+
+### Global Variable List: `GVL_Perf`
+
+```st
+VAR_GLOBAL
+    // 1000-DINT array — exercised by the bulk Sum-read benchmark.
+    aTags       : ARRAY[1..1000] OF DINT;
+    fbPerfChurn : FB_PerfChurn;
+END_VAR
+```
+
+The XAE-form GVL ships at `PLC/GVLs/GVL_Perf.TcGVL`; import it into the PLC
+project alongside `GVL_Fixture`.
+
+### POU: `FB_PerfChurn`
+
+```st
+FUNCTION_BLOCK FB_PerfChurn
+VAR
+    nIndex : INT := 1;
+END_VAR
+
+GVL_Perf.aTags[nIndex] := GVL_Perf.aTags[nIndex] + 1;
+nIndex := nIndex + 1;
+IF nIndex > 1000 THEN
+    nIndex := 1;
+END_IF
+```
+
+The XAE-form POU ships at `PLC/POUs/FB_PerfChurn.TcPOU`. Wire it into `MAIN`
+so a value rotates each cycle:
+
+```st
+PROGRAM MAIN
+VAR
+END_VAR
+
+// existing GVL_Fixture line:
+GVL_Fixture.nCounter := GVL_Fixture.nCounter + 1;
+
+// PR 2.1 — keep aTags moving so caches don't short-circuit the read.
+GVL_Perf.fbPerfChurn();
+```
+
+### Running the perf tier
+
+```powershell
+$env:TWINCAT_TARGET_HOST  = '10.0.0.42'
+$env:TWINCAT_TARGET_NETID = '5.23.91.23.1.1'
+$env:TWINCAT_PERF         = '1'
+dotnet test tests\ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.IntegrationTests `
+    --filter "Category=Performance"
+```
+
+Without `TWINCAT_PERF=1` the perf test skips via `[TwinCATPerfFact]` even when
+the runtime is reachable — perf runs are opt-in to keep the default integration
+pass fast.
+
 ### Runtime ID
 
 - TC3 PLC runtime 1 (AMS port `851`) — the smoke-test fixture defaults