Auto: focas-f4a — write infrastructure + per-tag opt-in

Closes #268

scripts/e2e/test-focas.ps1

@@ -26,6 +26,14 @@
 
 .PARAMETER BridgeNodeId
   NodeId at which the server publishes the Address.
+
+.PARAMETER Write
+  Issue #268 / plan PR F4-a — opts the script into the post-F4-a write
+  stages. F4-a ships the write infrastructure (driver-level Writes.Enabled
+  flag + per-tag Writable opt-in) without any actual wire writes; F4-b/c
+  populate this stage with real macro / parameter / PMC write coverage.
+  Until then the switch is a no-op marker so the e2e harness records that
+  the write surface was deliberately exercised (or skipped).
 #>
 
 param(
@@ -33,7 +41,8 @@ param(
     [int]$CncPort = 8193,
     [string]$Address = "R100",
     [string]$OpcUaUrl = "opc.tcp://localhost:4840",
-    [Parameter(Mandatory)] [string]$BridgeNodeId
+    [Parameter(Mandatory)] [string]$BridgeNodeId,
+    [switch]$Write
 )
 
 $ErrorActionPreference = "Stop"
@@ -92,5 +101,13 @@ $results += Test-SubscribeSeesChange `
     -DriverWriteArgs (@("write") + $commonFocas + @("-a", $Address, "-t", "Int16", "-v", $subValue)) `
     -ExpectedValue "$subValue"
 
+if ($Write) {
+    # F4-a no-op stage. Real per-kind write coverage lands in F4-b/c which extend the wire
+    # client past the BadNotSupported short-circuit + populate this branch with
+    # macro / parameter / PMC write assertions. Logged here so the harness records that the
+    # operator deliberately requested the write path.
+    Write-Host "[skip] -Write requested; F4-a ships infrastructure only — wire-write stages land in F4-b/c (issue #268)."
+}
+
 Write-Summary -Title "FOCAS e2e" -Results $results
 if ($results | Where-Object { -not $_.Passed }) { exit 1 }