Can't return Results on Tanstack Start server functions

[Joseevb]

When creating a Tanstack Start server function

class TestError extends TaggedError('TestError')<{ message: string }>() {}

const testServerFn = createServerFn().handler(() => {
  const random = Math.random()

  let result

  if (random < 0.5) {
    result = Result.ok('Success!')
  } else {
    result = Result.err(new TestError({ message: 'Something went wrong!' }))
  }

  return Result.serialize(result)
})

TypeScript gives the following error:

Argument of type '() => SerializedResult<string, TestError>' is not assignable to parameter of type 'ServerFn<Register, Method, undefined, undefined, SerializedResult<string, TestError>>'.
Type 'SerializedResult<string, TestError>' is not assignable to type 'ValidateSerializableMapped<SerializedOk, RegisteredSerializableInput> | ValidateSerializableMapped<...>'.
Type 'SerializedErr' is not assignable to type 'ValidateSerializableMapped<SerializedOk, RegisteredSerializableInput> | ValidateSerializableMapped<...>'.
Type 'SerializedErr' is not assignable to type 'ValidateSerializableMapped<SerializedErr, RegisteredSerializableInput>'.
The types of 'error.cause' are incompatible between these types.
Type 'unknown' is not assignable to type 'SerializationError<"Type may not be serializable"> | undefined'.

Without the Result.serialize()

class TestError extends TaggedError('TestError')<{ message: string }>() {}

const testServerFn = createServerFn().handler(() => {
  const random = Math.random()

  let result

  if (random < 0.5) {
    result = Result.ok('Success!')
  } else {
    result = Result.err(new TestError({ message: 'Something went wrong!' }))
  }

  return result
})

Argument of type '() => SerializedResult<string, TestError>' is not assignable to parameter of type 'ServerFn<Register, Method, undefined, undefined, SerializedResult<string, TestError>>'.
Type 'SerializedResult<string, TestError>' is not assignable to type 'ValidateSerializableMapped<SerializedOk, RegisteredSerializableInput> | ValidateSerializableMapped<...>'.
Type 'SerializedErr' is not assignable to type 'ValidateSerializableMapped<SerializedOk, RegisteredSerializableInput> | ValidateSerializableMapped<...>'.
Type 'SerializedErr' is not assignable to type 'ValidateSerializableMapped<SerializedErr, RegisteredSerializableInput>'.
The types of 'error.cause' are incompatible between these types.
Type 'unknown' is not assignable to type 'SerializationError<"Type may not be serializable"> | undefined'.

This makes it impossible to return the plain Result object on the server functions and handle them on the client/caller. How could this be solved?

[Joseevb]

This only happens when using TaggedErrors, when passing a plain object it's solved:

const testServerFn = createServerFn().handler(() => {
  const random = Math.random()

  let result

  if (random < 0.5) {
    result = Result.ok('Success!')
  } else {
    result = Result.err({ message: 'Something went wrong' })
  }

  return Result.serialize(result)
})