[Fusion] Do not apply "InferKeysFromLookups" to invalid lookup fields

src/HotChocolate/Fusion/src/Fusion.Composition/SourceSchemaPreprocessor.cs

@@ -388,7 +388,15 @@ private void InferKeysFromLookups()
         var lookupFieldDefinitions =
             schema.Types
                 .OfType<MutableComplexTypeDefinition>()
-                .SelectMany(t => t.Fields.AsEnumerable().Where(f => f.Directives.ContainsName(Lookup)));
+                .SelectMany(t => t.Fields.AsEnumerable().Where(f =>
+                {
+                    if (f.Arguments.Count == 0 || f.Type.IsNonNullType() || f.Type.IsListType())
+                    {
+                        return false;
+                    }
+
+                    return f.Directives.ContainsName(Lookup);
+                }));
 
         foreach (var lookupFieldDefinition in lookupFieldDefinitions)
         {

src/HotChocolate/Fusion/test/Fusion.Composition.Tests/SourceSchemaPreprocessorTests.cs

@@ -359,6 +359,44 @@ type Person {
         Assert.False(schema.Types["Person"].Directives.ContainsName(WellKnownDirectiveNames.Key));
     }
 
+    [Fact]
+    public void Preprocess_InferKeysFromLookups_DoesNotApplyToInvalidLookups()
+    {
+        // arrange
+        var sourceSchemaText =
+            new SourceSchemaText(
+                "A",
+                """
+                type Query {
+                    personById(id1: ID!): Person @lookup
+                    personByIdNoArguments: Person @lookup
+                    personByIdNonNull(id2: ID!): Person! @lookup
+                    personByIdListType(id3: ID!): [Person] @lookup
+                }
+
+                type Person {
+                    id: ID!
+                }
+                """);
+        var compositionLog = new CompositionLog();
+        var sourceSchemaParser = new SourceSchemaParser(sourceSchemaText, compositionLog);
+        var schema = sourceSchemaParser.Parse().Value;
+        var preprocessor =
+            new SourceSchemaPreprocessor(
+                schema,
+                [],
+                compositionLog);
+
+        // act
+        var result = preprocessor.Preprocess();
+
+        // assert
+        Assert.True(result.IsSuccess);
+        Assert.Single(
+            schema.Types["Person"].Directives.Where(
+                d => d.Name == WellKnownDirectiveNames.Key).ToArray());
+    }
+
     [Fact]
     public void Preprocess_InheritInterfaceKeysEnabled_InheritsInterfaceKeys()
     {