feat(windows): add recoverable existing-agent credential upgrade

agents/windows/tests/Test-MinerOpsNativeHarnessGetItemState.ps1

@@ -0,0 +1,48 @@
+[CmdletBinding()]
+param(
+    [Parameter(Mandatory = $true)]
+    [ValidateSet("NoExistingFunction", "ExistingFunction")]
+    [string]$Mode,
+    [Parameter(Mandatory = $true)][string]$SupportPath
+)
+
+$ErrorActionPreference = "Stop"
+. $SupportPath
+
+if ($Mode -ceq "NoExistingFunction") {
+    $before = Get-MinerOpsNativeGetItemState
+    if ([bool]$before.FunctionExisted) {
+        throw "Child process unexpectedly began with a global Get-Item function."
+    }
+    $observed = @(Invoke-MinerOpsNativeGetItemTrace -Action {
+        Get-Item -LiteralPath $SupportPath
+    })
+    if ($observed -cnotcontains $SupportPath) {
+        throw "Trace did not observe Get-Item."
+    }
+    Assert-MinerOpsNativeGetItemState -Expected $before `
+        -Context "no-preexisting-function child test"
+    return
+}
+
+$existing = { param($LiteralPath) "preexisting:$LiteralPath" }
+Set-Item -LiteralPath "Function:\global:Get-Item" -Value $existing -Force
+$before = Get-MinerOpsNativeGetItemState
+$observed = @(Invoke-MinerOpsNativeGetItemTrace -Action {
+    Get-Item -LiteralPath $SupportPath
+})
+if ($observed -cnotcontains $SupportPath) {
+    throw "Trace did not observe Get-Item over an existing global function."
+}
+$after = Get-MinerOpsNativeGetItemState
+Assert-MinerOpsNativeGetItemState -Expected $before `
+    -Context "preexisting-function child test"
+if ($after.FunctionScriptBlock.ToString() -cne $existing.ToString()) {
+    throw "Existing Get-Item ScriptBlock was not restored exactly."
+}
+if (-not [object]::ReferenceEquals(
+    $after.FunctionScriptBlock,
+    $before.FunctionScriptBlock
+)) {
+    throw "Existing Get-Item ScriptBlock instance changed."
+}