Make Windows PATH install idempotent

install.ps1

@@ -299,6 +299,26 @@ function Assert-SafeUpdateCache($Path) {
     $full
 }
 
+function Add-UserPath($PathToAdd) {
+    $userPath = [Environment]::GetEnvironmentVariable("Path", "User")
+    $entries = @()
+    if ($userPath) {
+        $entries = @($userPath -split ';' | Where-Object { $_ })
+    }
+    $wanted = Normalize-PathForCompare $PathToAdd
+    foreach ($entry in $entries) {
+        if ((Normalize-PathForCompare $entry) -ieq $wanted) {
+            return
+        }
+    }
+    $next = if ($entries.Count -gt 0) {
+        (@($entries) + $PathToAdd) -join ';'
+    } else {
+        $PathToAdd
+    }
+    [Environment]::SetEnvironmentVariable("Path", $next, "User")
+}
+
 $bindir = Join-Path $Prefix "bin"
 $configDir = Join-Path $HOME ".config\dosh"
 New-Item -ItemType Directory -Force -Path $bindir, $configDir | Out-Null
@@ -447,10 +467,7 @@ predict = true
 "@ | Set-Content -NoNewline -Encoding utf8 $hostsConfig
 }
 
-$userPath = [Environment]::GetEnvironmentVariable("Path", "User")
-if (-not (($userPath -split ';') -contains $bindir)) {
-    [Environment]::SetEnvironmentVariable("Path", "$userPath;$bindir", "User")
-}
+Add-UserPath $bindir
 
 Write-Host "Installed Dosh client to $bindir"
 Write-Host "Configured UDP port $Port"

tests/release_scripts.rs

@@ -145,6 +145,20 @@ fn windows_installer_reuses_persistent_source_update_cache() {
     );
 }
 
+#[test]
+fn windows_installer_adds_user_path_idempotently() {
+    let ps1 = include_str!("../install.ps1");
+    assert!(ps1.contains("function Add-UserPath($PathToAdd)"));
+    assert!(ps1.contains("$wanted = Normalize-PathForCompare $PathToAdd"));
+    assert!(ps1.contains("-ieq $wanted"));
+    assert!(ps1.contains("(@($entries) + $PathToAdd) -join ';'"));
+    assert!(
+        !ps1.contains("\"$userPath;$bindir\""),
+        "Windows installer must not write a leading semicolon when user PATH is empty"
+    );
+    assert!(ps1.contains("Add-UserPath $bindir"));
+}
+
 #[test]
 fn unix_installer_rejects_unsafe_source_update_cache_paths() {
     let install = include_str!("../install.sh");