fix(ci): run nested smoke scripts on same host + UTF-8 BOM

Windows CI failed because smoke.ps1 nested bare 'powershell' (often 5.1)
to run verify-routing-coherence.ps1. PS5.1 mis-parsed UTF-8 Chinese source
without BOM, so nested verify exited 1 while the standalone pwsh verify step passed.

- Resolve SmokeHostExe from current process (pwsh on GHA windows-latest)
- Rewrite nested invocations to use $SmokeHostExe
- Write UTF-8 BOM on smoke.ps1 and verify-routing-coherence.ps1 for PS5.1 safety

skills/scripts/smoke.ps1

@@ -28,7 +28,23 @@ function Bad([string] $m) {
     [void]$fail.Add($m)
 }
 
-Write-Host ("=== reverse-skill smoke | LogDir={0} ===" -f $LogDir)
+# Prefer the same host that launched smoke (pwsh on GHA windows-latest).
+# Bare "powershell" often resolves to Windows PowerShell 5.1, which mis-parses
+# UTF-8 scripts without BOM when nested from pwsh.
+$SmokeHostExe = $null
+try {
+    $procPath = (Get-Process -Id $PID -ErrorAction Stop).Path
+    if ($procPath -and (Test-Path -LiteralPath $procPath)) { $SmokeHostExe = $procPath }
+} catch { }
+if (-not $SmokeHostExe) {
+    $cmd = Get-Command pwsh -ErrorAction SilentlyContinue
+    if ($cmd -and $cmd.Source) {
+        $SmokeHostExe = $cmd.Source
+    } else {
+        $SmokeHostExe = Join-Path $env:SystemRoot 'System32\WindowsPowerShell\v1.0\powershell.exe'
+    }
+}
+Write-Host ("=== reverse-skill smoke | LogDir={0} | Host={1} ===" -f $LogDir, $SmokeHostExe)
 
 # --- 1) routing coherence ---
 $verify = Join-Path $scriptDir 'verify-routing-coherence.ps1'
@@ -37,7 +53,7 @@ if (-not (Test-Path -LiteralPath $verify)) {
     $verifyExit = 1
 } else {
     $vLog = Join-Path $LogDir '01-verify.txt'
-    & powershell -NoProfile -ExecutionPolicy Bypass -File $verify 2>&1 | Tee-Object -FilePath $vLog | Out-Null
+    & $SmokeHostExe -NoProfile -ExecutionPolicy Bypass -File $verify 2>&1 | Tee-Object -FilePath $vLog | Out-Null
     $verifyExit = $LASTEXITCODE
     if ($verifyExit -eq 0) { Ok 'verify-routing-coherence exit 0' } else { Bad ("verify-routing-coherence exit {0}" -f $verifyExit) }
 }
@@ -106,7 +122,7 @@ if (-not (Test-Path -LiteralPath $mr)) {
 } else {
     foreach ($c in $cases) {
         $outFile = Join-Path $LogDir ("route-{0}.txt" -f $c.Name)
-        $raw = & powershell -NoProfile -ExecutionPolicy Bypass -File $mr -Hint $c.Hint 2>&1 | Out-String
+        $raw = & $SmokeHostExe -NoProfile -ExecutionPolicy Bypass -File $mr -Hint $c.Hint 2>&1 | Out-String
         $raw | Set-Content -Path $outFile -Encoding UTF8
         if ($raw -match [regex]::Escape($c.Expect)) {
             Ok ("route {0} -> {1}" -f $c.Name, $c.Expect)
@@ -128,7 +144,7 @@ if (-not (Test-Path -LiteralPath $appendEvidence)) {
     Bad 'append-evidence.ps1 missing for immutability check'
 } else {
     New-Item -ItemType Directory -Path $evidenceCase -Force | Out-Null
-    & powershell -NoProfile -ExecutionPolicy Bypass -File $appendEvidence `
+    & $SmokeHostExe -NoProfile -ExecutionPolicy Bypass -File $appendEvidence `
         -CaseRoot $evidenceCase `
         -Id 'E-IMMUTABLE' `
         -Title 'first write' `
@@ -142,7 +158,7 @@ if (-not (Test-Path -LiteralPath $appendEvidence)) {
         $beforeEvidence = (Get-FileHash -LiteralPath $evidencePath -Algorithm SHA256).Hash
         $beforeIndex = (Get-FileHash -LiteralPath $indexPath -Algorithm SHA256).Hash
 
-        & powershell -NoProfile -ExecutionPolicy Bypass -File $appendEvidence `
+        & $SmokeHostExe -NoProfile -ExecutionPolicy Bypass -File $appendEvidence `
             -CaseRoot $evidenceCase `
             -Id 'E-IMMUTABLE' `
             -Title 'second write' `

skills/scripts/verify-routing-coherence.ps1

@@ -1,4 +1,4 @@
-#Requires -Version 5.1
+#Requires -Version 5.1
 # reverse-skill routing + ops contract gates (skill-router only; no host platform runtime)
 param([string] $ScratchDir = '')
 $ErrorActionPreference = 'Stop'