How to keep specs consistent and up-to-date with spec-kit?

With `spec-kit`, each feature defines its own spec. This works well at first, but over time and with the multiplication of features, some descriptions become outdated or are enriched by new features.

## Example

- Feature **001 – User Login** defines that a user can log in with email + password.
- A few months later, feature **009 – Two-Factor Authentication** enhances the login by adding an extra step (OTP code).

In this case, the original spec of feature 001 becomes partially outdated or needs to be complemented by feature 009.

## Discussion

- Is there a recommended approach to **consolidate specs over time**?
- Should the original feature be modified, or is it better to keep the historical record and add links to subsequent evolutions?
- Are there patterns used by the community to manage the evolution and consistency of specs as new features are added?
- **Idea:** Would it be useful to introduce a `/close` command (or equivalent) to mark a feature as deprecated and automatically update a centralized project documentation?