NickJosevski · Aug 12, 2026 · Aug 12, 2026
diff --git a/source/Calamari.Common/Features/Scripting/DotnetScript/DotnetScriptBootstrapper.cs b/source/Calamari.Common/Features/Scripting/DotnetScript/DotnetScriptBootstrapper.cs
@@ -102,11 +102,31 @@ public static string FormatCommandArguments(string bootstrapFile, string? script
             var source = string.IsNullOrWhiteSpace(nugetSource) ? "https://api.nuget.org/v3/index.json" : nugetSource;
             var commandArguments = new StringBuilder();
             commandArguments.Append($"-s {source} ");
+            // dotnet-script 2.0 turned the isolated assembly load context on by default, which
+            // changes which assembly a script gets when it references a package that dotnet-script
+            // also carries: a script asking for Newtonsoft.Json 9.0.1 used to bind to the 13.0.3
+            // dotnet-script bundles, and under isolation it gets 9.0.1. That is arguably more
+            // correct, but it is a silent change to what customer scripts run against, so hold the
+            // existing behaviour here and treat adopting isolation as its own decision.
+            //
+            // Unless the customer asked for isolation themselves. When both flags are passed,
+            // --disable-isolated-load-context wins, so adding it unconditionally would override
+            // the one group of customers who made a deliberate choice here.
+            if (!HasIsolatedLoadContextFlag(scriptCommandArguments))
+                commandArguments.Append("--disable-isolated-load-context ");
             if (!string.IsNullOrWhiteSpace(scriptCommandArguments)) commandArguments.Append($"{scriptCommandArguments} ");
             commandArguments.AppendFormat("\"{0}\" -- {1} \"{2}\"", bootstrapFile, scriptArguments, encryptionKey);
             return commandArguments.ToString();
         }
 
+        /// <summary>
+        /// True when the caller already passed --isolated-load-context. Note that
+        /// --disable-isolated-load-context does not match: "--isolated-load-context" is not a
+        /// substring of it, because the character before "isolated" there is a single dash.
+        /// </summary>
+        static bool HasIsolatedLoadContextFlag(string? scriptCommandArguments)
+            => scriptCommandArguments?.IndexOf("--isolated-load-context", StringComparison.OrdinalIgnoreCase) >= 0;
+
         [return: NotNullIfNotNull("scriptParameters")]
         static (string? scriptCommandArguments, string? scriptArguments) RetrieveParameterValues(string? scriptParameters)
         {

diff --git a/source/Calamari.Scripting/DotnetScript/dotnet-script.1.6.0.zip b/source/Calamari.Scripting/DotnetScript/dotnet-script.1.6.0.zip
diff --git a/source/Calamari.Scripting/DotnetScript/dotnet-script.2.0.1.zip b/source/Calamari.Scripting/DotnetScript/dotnet-script.2.0.1.zip
diff --git a/source/Calamari.Scripting/DotnetScript/dotnet-script.runtimeconfig.json b/source/Calamari.Scripting/DotnetScript/dotnet-script.runtimeconfig.json
@@ -0,0 +1,14 @@
+{
+  "runtimeOptions": {
+    "tfm": "net8.0",
+    "rollForward": "LatestMajor",
+    "framework": {
+      "name": "Microsoft.NETCore.App",
+      "version": "8.0.0"
+    },
+    "configProperties": {
+      "System.Reflection.Metadata.MetadataUpdater.IsSupported": false,
+      "System.Runtime.Serialization.EnableUnsafeBinaryFormatterSerialization": false
+    }
+  }
+}
diff --git a/source/Calamari.Tests/Fixtures/DotnetScript/DotnetScriptBootstrapperFixture.cs b/source/Calamari.Tests/Fixtures/DotnetScript/DotnetScriptBootstrapperFixture.cs
@@ -22,6 +22,23 @@ public void FormatCommandArgumentsTest([CanBeNull] string scriptParameters, [Can
             formattedCommandArgument.Should().Contain($"{commandArguments}\"{bootstrapFile}\" -- {scriptArguments}");
         }
 
+        [Test]
+        public void FormatCommandArguments_DisablesIsolatedLoadContext_ByDefault()
+        {
+            var result = DotnetScriptBootstrapper.FormatCommandArguments("Bootstrap.csx", null);
+            result.Should().Contain("--disable-isolated-load-context ");
+        }
+
+        [TestCase("--isolated-load-context -- \"Parameter 1\"")]
+        [TestCase("--isolated-load-context -d -- \"Parameter 1\"")]
+        public void FormatCommandArguments_LeavesIsolationOn_WhenTheCallerAskedForIt(string scriptParameters)
+        {
+            // Both flags together resolve to disabled, so we must not add ours on top of theirs.
+            var result = DotnetScriptBootstrapper.FormatCommandArguments("Bootstrap.csx", scriptParameters);
+            result.Should().NotContain("--disable-isolated-load-context");
+            result.Should().Contain("--isolated-load-context ");
+        }
+
         [Test]
         public void FormatCommandArguments_UsesCustomNuGetSource_WhenProvided()
         {

diff --git a/source/IncludeDotNetScript.targets b/source/IncludeDotNetScript.targets
@@ -3,13 +3,23 @@
     <Target Name="GetToolFiles" DependsOnTargets="RunResolvePackageDependencies">
         <ItemGroup>
             <DotnetScriptFiles Include="$(MSBuildProjectDirectory)/../Calamari.Scripting/DotnetScript/dotnet-script.*.zip"/>
+            <!--
+                Overwrites the runtimeconfig.json extracted from the zip. The upstream file requests
+                Microsoft.NETCore.App 8.0.0 with no rollForward, so the default Minor policy binds to
+                an 8.x runtime and nothing else: dotnet-script fails to launch (exit 150) on a target
+                that only has a newer runtime, and stays on .NET 8 on a target that has both.
+                Ours adds "rollForward": "LatestMajor". Keep it in sync with the zip when the
+                bundled dotnet-script version changes - the rest of the file is upstream's.
+            -->
+            <DotnetScriptRuntimeConfig Include="$(MSBuildProjectDirectory)/../Calamari.Scripting/DotnetScript/dotnet-script.runtimeconfig.json"/>
         </ItemGroup>
     </Target>
     <Target Name="CopyDotnetScriptFilesAfterBuild" AfterTargets="Build" DependsOnTargets="GetToolFiles">
         <ItemGroup>
             <DotnetScriptFilesExe Include="$(OutputPath)/dotnet-script/*.sh;$(OutputPath)/dotnet-script/*.exe"/>
         </ItemGroup>
         <Unzip SourceFiles="@(DotnetScriptFiles)" DestinationFolder="$(OutputPath)/" />
+        <Copy SourceFiles="@(DotnetScriptRuntimeConfig)" DestinationFolder="$(OutputPath)/dotnet-script/" />
         <Exec Command="chmod +x %(DotnetScriptFilesExe.Identity)" IgnoreExitCode="true" Condition="!$([MSBuild]::IsOSPlatform('Windows'))"/>
     </Target>
 
@@ -18,6 +28,7 @@
             <DotnetScriptFilesExe Include="$(PublishDir)/dotnet-script/*.sh;$(PublishDir)/dotnet-script/*.exe"/>
         </ItemGroup>
         <Unzip SourceFiles="@(DotnetScriptFiles)" DestinationFolder="$(PublishDir)/" />
+        <Copy SourceFiles="@(DotnetScriptRuntimeConfig)" DestinationFolder="$(PublishDir)/dotnet-script/" />
         <Exec Command="chmod +x %(DotnetScriptFilesExe.Identity)" IgnoreExitCode="true" Condition="!$([MSBuild]::IsOSPlatform('Windows'))"/>
     </Target>
 </Project>