feat: Add winexec helper for running PowerShell from the agent

internal/winexec/encode.go

@@ -0,0 +1,24 @@
+// Package winexec runs PowerShell on Windows hosts.
+//
+// It exists because three subsystems — updates, workload collection and
+// workload logs — all need the same invocation, and because getting a
+// multi-line script past Go quoting, cmd.exe quoting and PowerShell's own
+// parser is a problem worth solving once.
+package winexec
+
+import (
+	"encoding/base64"
+	"unicode/utf16"
+)
+
+// EncodeCommand renders a script for powershell.exe -EncodedCommand: UTF-16LE,
+// no byte-order mark, base64. This is deliberately free of build tags so it is
+// tested on a Linux development machine like every other pure function here.
+func EncodeCommand(script string) string {
+	units := utf16.Encode([]rune(script))
+	b := make([]byte, 0, len(units)*2)
+	for _, u := range units {
+		b = append(b, byte(u), byte(u>>8))
+	}
+	return base64.StdEncoding.EncodeToString(b)
+}