Build the F# packages against the host's FSharp.Core, and reopen the namespaces in a C# notebook

Sources/AngouriMath/extension.dib

@@ -34,3 +34,16 @@ if (FindType("Numbers", "PeterO.Numbers.ERational") is { } rational)
     RegisterLatex(rational, o => $@"\frac{{{rational.GetProperty("Numerator").GetValue(o)}}}{{{rational.GetProperty("Denominator").GetValue(o)}}}");
 
 "Extensions for LaTeX loaded!"
+
+#!csharp
+
+// The namespaces a C# notebook writes without opening: `AngouriMath` and `AngouriMath.Extensions` are opened only
+// when the cell above was compiled against AngouriMath, which is when this kernel loaded the package rather than
+// another kernel of the same notebook, and the opening is deferred to this kernel's next submission.
+static object PropertyOf(object o, string name) => o?.GetType().GetProperty(name)?.GetValue(o);
+
+if (PropertyOf(PropertyOf(PropertyOf(Microsoft.DotNet.Interactive.Kernel.Current, "ScriptState"), "Script"), "Options") is { } options
+    && PropertyOf(options, "MetadataReferences") is System.Collections.IEnumerable references
+    && references.Cast<object>().Any(r => PropertyOf(r, "Display") is string path && System.IO.Path.GetFileName(path) == "AngouriMath.dll"))
+    Microsoft.DotNet.Interactive.Kernel.Current.DeferCommand(
+        new Microsoft.DotNet.Interactive.Commands.SubmitCode("using AngouriMath;\nusing AngouriMath.Extensions;"));

Sources/Tests/InteractiveWrapperUnitTests/HostCompatibility.fs

@@ -0,0 +1,28 @@
+//
+// Copyright (c) 2019-2026 Angouri.
+// AngouriMath is licensed under MIT.
+// Details: https://github.com/asc-community/AngouriMath/blob/master/LICENSE.md.
+// Website: https://am.angouri.org.
+//
+
+module AngouriMath.Interactive.Tests.HostCompatibility
+
+open System.Reflection
+open Xunit
+
+let private fsharpCoreReferencedBy (assembly : Assembly) =
+    assembly.GetReferencedAssemblies()
+    |> Array.find (fun name -> name.Name = "FSharp.Core")
+    |> fun name -> name.Version
+
+// A notebook host runs its own FSharp.Core and cannot give a package a newer one. Built against
+// FSharp.Core 10.1 under a host carrying 10.0, the kernel extension hung a C# kernel as it loaded,
+// and an F# kernel failed its first call into the wrappers unless the extension had loaded first:
+// https://github.com/asc-community/AngouriMath/issues/2108
+[<Fact>]
+let ``The wrappers ask for no newer FSharp.Core than the F# kernel is built against`` () =
+    let kernel = fsharpCoreReferencedBy typeof<Microsoft.DotNet.Interactive.FSharp.FSharpKernel>.Assembly
+    for wrapper in [ typeof<AngouriMath.InteractiveExtension.KernelExtension>.Assembly
+                     Assembly.Load "AngouriMath.FSharp" ] do
+        let asked = fsharpCoreReferencedBy wrapper
+        Assert.True(asked <= kernel, $"{wrapper.GetName().Name} asks for FSharp.Core {asked}, the F# kernel is built against {kernel}")

Sources/Tests/InteractiveWrapperUnitTests/InteractiveWrapperUnitTests.fsproj

@@ -10,6 +10,7 @@
   <ItemGroup>
     <Compile Include="AggressiveOperators.fs" />
     <Compile Include="HtmlOutput.fs" />
+    <Compile Include="HostCompatibility.fs" />
     <Compile Include="Program.fs" />
   </ItemGroup>
 

Sources/Wrappers/AngouriMath.FSharp/AngouriMath.FSharp.fsproj

@@ -27,6 +27,13 @@
     <Compile Include="Matrices.fs" />
   </ItemGroup>
 
+  <ItemGroup>
+    <!-- A notebook host runs its own FSharp.Core, so the wrappers ask for the lowest one they build
+         against rather than the SDK's: 8.0.403 is Plotly.NET's floor, and 10.1 hung a C# kernel under a
+         host carrying 10.0. https://github.com/asc-community/AngouriMath/issues/2108 -->
+    <PackageReference Update="FSharp.Core" Version="8.0.403" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\..\AngouriMath\AngouriMath.csproj" />
   </ItemGroup>

Sources/Wrappers/AngouriMath.Interactive/AngouriMath.Interactive.fsproj

@@ -47,6 +47,10 @@
     <PackageReference Include="Microsoft.DotNet.Interactive" Version="1.0.0-beta.23611.1" />
     <PackageReference Include="Microsoft.DotNet.Interactive.Formatting" Version="1.0.0-beta.23611.1" />
     <PackageReference Include="Plotly.NET" Version="6.0.0-preview.1" />
+    <!-- A notebook host runs its own FSharp.Core, so the wrappers ask for the lowest one they build
+         against rather than the SDK's: 8.0.403 is Plotly.NET's floor, and 10.1 hung a C# kernel under a
+         host carrying 10.0. https://github.com/asc-community/AngouriMath/issues/2108 -->
+    <PackageReference Update="FSharp.Core" Version="8.0.403" />
   </ItemGroup>
 
   <ItemGroup>