Schema arguments aren't validated

[suzuki-shunsuke]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

https://play.kcl-lang.io/?s=M4YwFgpgtghgBAVWBATgbRig5gLjgQWwF0cAoOCuAOxigj2ABcU4BeOAIgBIBvTLAHQQqANwBytCAF8OpUqEiwC2MpTjDxkvByYwsASypYOcAD6cADigD2AEwCuIRvutVZpAPr3kLdklQAFDxSAJRyXj5AA

schema User[arg: Arg]:
    name: str = "${arg.envName}"

schema Arg:
    envName: "staging" | "production"

_user = User({})

_user

kcl hello.k 

2. What did you expect to see? (Required)

An error occurs because the argument {} doesn't meet Arg.

Error: EvaluationError
 --> /Users/shunsukesuzuki/Documents/test/kcl/validation/hello.k:7:1
  |
7 | _user = User({})
  |  attribute 'envName' of Arg is required and can't be None or Undefined
  |

3. What did you see instead (Required)

KCL doesn't raise error. Instead, Undefined is outputted.

name: Undefined

4. What is your KCL components version? (Required)

$ kcl version
0.11.2

Note

Discussion on Slack: https://cloud-native.slack.com/archives/C05TC96NWN8/p1748181426486519

https://play.kcl-lang.io/?s=M4YwFgpgtghgBAVWBATgbRig5gLjgQWwF0cAoOCuAfUyzgF45bzKA7GKCPYAFxQbgAiACQBvWgDoIrAG4A5DhAC+g0qVCRYBbGUpxp8xXkG8YWAJassguAB8hABxQB7ACYBXED3PPWq0lTuyPyMSKgAFKJKAJRqgcGkQA

When I add _arg = arg to the schema User, arg is validated properly.

schema User[arg: Arg]:
    _arg = arg
    name: str = "${arg.envName}"

$ kcl hello.k
Error: EvaluationError
 --> /Users/shunsukesuzuki/Documents/test/kcl/validation/hello.k:8:1
  |
8 | _user = User({})
  |  attribute 'envName' of Arg is required and can't be None or Undefined
  |