PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

classValidatorShim can emit enum metadata from @IsIn(...), but when the plugin falls back to type: () => Object for a literal-union property, 11.4.1 keeps type: object in the generated schema. That produces an invalid schema for downstream tools.

Issue Number: N/A

What is the new behavior?

When schema metadata has enum and the inferred type is the plugin fallback Object, SchemaObjectFactory now infers the scalar schema type from the enum values instead of keeping object.

Example output:

{
  "type": "string",
  "enum": ["a", 1]
}

Does this PR introduce a breaking change?

• Yes
• No

Other information

• Added regression coverage in test/services/schema-object-factory.spec.ts for type: () => Object + enum metadata.
• Added plugin coverage in test/plugin/model-class-visitor.spec.ts for @IsIn(['a', 1]) on a literal-union property.