Fix IList<T> misclassified as interface on mutation error types

[glen-84]

Summary

Schema build for a mutation using FieldResult<TResult, TError> fails when the error type has a member typed as an array or collection interface (int[], IList<T>, ICollection<T>, IEnumerable<T>, IReadOnlyList<T>, ...). MutationConventionTypeInterceptor.EnsureTypeReferenceRegistered passed those raw to the type-discovery pipeline. For IList<int>, TypeDiscoveryInfo.IsInterface was set from TypeAttributes.Interface and the type got registered as InterfaceType<IList<Int32>>, surfacing as There is no object type implementing interface `ListOfInt32` under strict validation. For int[], the same path crashed earlier with ArgumentNullException in TryRegisterType.

The fix unwraps IsArrayOrList references to their ElementType before inference so the wrapper never reaches the discovery handler. A while loop handles nested cases (IList<IList<T>>).

Test plan

• New regression test Error_Type_With_IList_Property_Should_Be_Treated_As_List in AnnotationBasedMutations.cs — record-shape error type with an IList<int> positional parameter, asserts field type is [Int!]! and no spurious *List* interfaces are registered.
• Empirically verified that swapping the fixture's IList<int> for int[] was also broken pre-fix and is resolved by the same unwrap.
• Full Mutations test suite green on net8 / net9 / net10 (98/98).

[Copilot]

Pull request overview

Fixes a schema-build failure in mutation conventions where CLR collection types on mutation error objects (e.g., IList<T>, arrays) could be incorrectly forwarded into type discovery and registered as GraphQL interfaces, leading to strict validation errors (and in some cases earlier crashes).

Changes:

• Unwraps IsArrayOrList runtime type references to their element type before schema type inference/registration in MutationConventionTypeInterceptor.
• Adds a regression test ensuring an error type with an IList<int> member is treated as a GraphQL list ([Int!]!) and does not register spurious interface types.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/HotChocolate/Core/src/Types.Mutations/MutationConventionTypeInterceptor.cs	Unwraps list/array runtime type references before calling schema type inference to avoid misclassification as interfaces.
src/HotChocolate/Core/test/Types.Mutations.Tests/AnnotationBasedMutations.cs	Adds regression coverage for IList<int> on error types to ensure correct list handling and prevent accidental interface registration.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.