Add regression test: #14596, type inference in task CE with recursive constraints

tests/FSharp.Compiler.ComponentTests/ConstraintSolver/TaskCETypeInference.fs

@@ -0,0 +1,41 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace FSharp.Compiler.ComponentTests.ConstraintSolver
+
+open Xunit
+open FSharp.Test.Compiler
+
+module TaskCETypeInference =
+
+    // https://github.com/dotnet/fsharp/issues/14596
+    [<Fact>]
+    let ``Issue 14596 - Type inference in backgroundTask CE should not produce FS0073`` () =
+        FSharp
+            """
+module UnresolvedTypeVarBug
+
+type IMarker<'T> = interface end
+type SomeAction<'T when 'T :> IMarker<'T>> = SomeAction of list<'T>
+type Spec<'Action> = { Dummy: unit }
+
+open System.Threading.Tasks
+
+let dummyTask (_spec: Spec<'Action>) (_action: 'Action) : Task<Result<unit, string>> = failwith "not implemented"
+
+let repro (spec: Spec<SomeAction<'T>>)
+    : Task<Result<unit, string>> =
+
+    backgroundTask {
+        let action = SomeAction []
+        let! res = dummyTask spec action
+
+        match res with
+        | Ok _ ->
+            return Ok ()
+        | Error err ->
+            return Error err
+    }
+            """
+        |> asLibrary
+        |> typecheck
+        |> shouldSucceed

tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj

@@ -403,6 +403,7 @@
     <Compile Include="ConstraintSolver\PrimitiveConstraints.fs" />
     <Compile Include="ConstraintSolver\MemberConstraints.fs" />
     <Compile Include="ConstraintSolver\ObjInference.fs" />
+    <Compile Include="ConstraintSolver\TaskCETypeInference.fs" />
     <Compile Include="Interop\DeeplyNestedCSharpClasses.fs" />
     <Compile Include="Interop\DIMSlotCoverageTests.fs" />
     <Compile Include="Interop\SimpleInteropTests.fs" />