[Feature] Raise an error when a custom `dbt_valid_to_current` is configured for a pre-existing snapshot

[dbeatty10]

Is this your first time submitting a feature request?

• [X] I have read the expectations for open source contributors
• [X] I have searched the existing issues, and I could not find an existing issue for this feature
• [X] I am requesting a straightforward extension of existing dbt functionality, rather than a Big Idea better suited to a discussion

Describe the feature

The dbt_valid_to_current config is intended for net-new snapshots rather than being applied to snapshots that already exist (i.e., the relevant table exists in the database). The reason is that dbt is not supplying automated migration paths (https://github.com/dbt-labs/dbt-core/issues/10325), and its up to users to migrate in the best way they see fit.

So similar to https://github.com/dbt-labs/dbt-core/issues/10185 for the snapshot_meta_column_names config, dbt should throw an error if the user has an existing snapshot and they try to add/change the dbt_valid_to_current config.

• this should error on insert if you change the meta field names, but [one idea] we could try to throw an error before running the snapshot DML by running adapters.get_columns_in_relation() on the existing snapshot and comparing the meta fields that exist in the current config to what exists in the warehouse

Describe alternatives you've considered

No response

Who will this benefit?

No response

Are you interested in contributing this feature?

No response

Anything else?

No response

[graciegoheen]

this should error on insert if you change the meta field names

This config doesn't change the name of the meta fields. It changes the value that means "current" for the dbt_valid_to field. How could we throw an error in that case?