diff --git a/scripts/install/Refresh-Services.ps1 b/scripts/install/Refresh-Services.ps1
index bd81e10b..40c441e4 100644
--- a/scripts/install/Refresh-Services.ps1
+++ b/scripts/install/Refresh-Services.ps1
@@ -118,6 +118,43 @@ Run {
         -c Release -o (Join-Path $PublishRoot "lmxopcua\WonderwareHistorian") | Out-Null
 } "dotnet publish (Host + sidecar)"
 
+# ------------------------------------------------------------------------
+# Step 4b: Assert the Wonderware historian sidecar deploy is COMPLETE
+# ------------------------------------------------------------------------
+# A partial/stale sidecar deploy (e.g. a hand-copy that bypassed the
+# `dotnet publish` above) silently drops the net48 binding-redirect
+# .exe.config and the transitive runtime DLLs MessagePack needs — most
+# notably System.Memory.dll. The sidecar then JIT-load-faults inside
+# PipeServer.RunOneConnectionAsync ("FileNotFoundException: System.Memory,
+# Version=4.0.1.2") and NSSM crash-loops it (exit 2 every ~2 min, ~120 s of
+# retry backoff before it gives up). Fail loudly here so an incomplete deploy
+# is caught at publish time instead of by a production crash-loop.
+# (Root-caused 2026-06-12; these four files have no alternate resolution path,
+# unlike the AVEVA SDK DLLs which the Historian install can also supply.)
+
+if (-not $WhatIf) {
+    Step "Verifying Wonderware historian sidecar deploy is complete"
+
+    $sidecarDir = Join-Path $PublishRoot "lmxopcua\WonderwareHistorian"
+    $sidecarRequired = @(
+        'OtOpcUa.Driver.Historian.Wonderware.exe',
+        'OtOpcUa.Driver.Historian.Wonderware.exe.config', # net48 binding redirects
+        'System.Memory.dll',                              # MessagePack's load-bearing dep
+        'MessagePack.dll'
+    )
+
+    $missing = $sidecarRequired | Where-Object { -not (Test-Path (Join-Path $sidecarDir $_)) }
+
+    if ($missing.Count -gt 0) {
+        $msg = "Wonderware historian sidecar deploy at '$sidecarDir' is INCOMPLETE — missing: " +
+               "$($missing -join ', '). It would crash-loop with a FileNotFoundException in PipeServer. " +
+               "Re-run the sidecar 'dotnet publish' into that folder (Step 4) — never hand-copy a partial build output."
+        throw $msg
+    }
+
+    Write-Host "  sidecar deploy OK — all $($sidecarRequired.Count) load-bearing files present" -ForegroundColor DarkGreen
+}
+
 # ------------------------------------------------------------------------
 # Step 5: Service env block — ensure OTOPCUA_HISTORIAN_ALARM_WRITE_ENABLED
 # is set on the Wonderware historian service (PR C.2 toggle).