Auto: focas-f4c — pmc_wrpmcrng with bit-level RMW

Closes #270

scripts/e2e/test-focas.ps1

@@ -47,6 +47,15 @@
   writes are the lowest-risk write surface (no parameter-write switch
   needed, no MDI mode required) so this stage runs whenever -Write is
   supplied.
+
+.PARAMETER PmcBitAddress
+  PMC bit address for the F4-c bit-write round-trip stage (default
+  R100.3). Only fires when -Write is supplied AND the operator
+  double-opts in via FOCAS_PMC_WRITE=1, mirroring the FOCAS_PARAM_WRITE
+  gate. PMC writes have a higher blast radius than PARAM/MACRO (a
+  mistargeted bit can move motion or latch a feedhold) so the gate is
+  off by default — see docs/v2/focas-deployment.md "Write safety / PMC
+  pre-checks".
 #>
 
 param(
@@ -57,7 +66,8 @@ param(
     [Parameter(Mandatory)] [string]$BridgeNodeId,
     [switch]$Write,
     [string]$ParamAddress = "PARAM:1815",
-    [string]$MacroAddress = "MACRO:500"
+    [string]$MacroAddress = "MACRO:500",
+    [string]$PmcBitAddress = "R100.3"
 )
 
 $ErrorActionPreference = "Stop"
@@ -146,6 +156,27 @@ if ($Write) {
     } else {
         Write-Host "[skip] FOCAS_PARAM_WRITE not set — parameter-write stage requires the CNC to be in MDI mode + parameter-write switch enabled (see docs/v2/focas-deployment.md 'Write safety')."
     }
+
+    # F4-c — PMC bit round-trip. PMC writes have a higher blast radius
+    # than PARAM/MACRO (a mistargeted bit can move motion or latch a
+    # feedhold) so the stage is gated on a separate FOCAS_PMC_WRITE=1
+    # opt-in. The bit write exercises the driver's read-modify-write
+    # path: write 'on' -> read returns 'on'; write 'off' -> read returns
+    # 'off'. Both halves run so a regression in either branch is caught.
+    if ($env:FOCAS_PMC_WRITE -eq "1" -or $env:FOCAS_PMC_WRITE -eq "true") {
+        $results += Test-DriverLoopback `
+            -Cli $focasCli `
+            -WriteArgs (@("write") + $commonFocas + @("-a", $PmcBitAddress, "-t", "Bit", "-v", "on")) `
+            -ReadArgs  (@("read")  + $commonFocas + @("-a", $PmcBitAddress, "-t", "Bit")) `
+            -ExpectedValue "True"
+        $results += Test-DriverLoopback `
+            -Cli $focasCli `
+            -WriteArgs (@("write") + $commonFocas + @("-a", $PmcBitAddress, "-t", "Bit", "-v", "off")) `
+            -ReadArgs  (@("read")  + $commonFocas + @("-a", $PmcBitAddress, "-t", "Bit")) `
+            -ExpectedValue "False"
+    } else {
+        Write-Host "[skip] FOCAS_PMC_WRITE not set — PMC bit-write round-trip is off by default because a mistargeted PMC bit can move motion or latch a feedhold (see docs/v2/focas-deployment.md 'PMC pre-checks')."
+    }
 }
 
 Write-Summary -Title "FOCAS e2e" -Results $results