Enforce a dbt model contract on an incremental model without breaking on_schema_change

Steps

1. Add contract: {enforced: true} to the model's config, or +contract: {enforced: true} at the project/folder level in dbt_project.yml.
2. Set on_schema_change to either append_new_columns or fail — dbt documents these as the only values compatible with a contracted incremental model.
3. Do not use on_schema_change: sync_all_columns on a contracted model — dbt explicitly calls this out as incompatible because it can drop columns, breaking the contract's guaranteed schema.
4. Declare the full column list with explicit data_type (and constraints where the warehouse supports them) in the model's YAML — the contract is enforced against this list, not inferred from the query.
5. Run a dbt build/test after any upstream schema change to confirm the model still compiles under the enforced contract before it reaches production.