[CT-2378] [Bug] state:modified not catching breaking changes if model body also changes

[jtcohen6]

If I change both the contract and the body of a model with an enforced contract, state:modified selects the model without raising the exception added in #6869 / #7216.

Repro case

models:
  - name: my_model
    config:
      contract:
        enforced: true
    columns:
      - name: id
        data_type: int

select 1 as id

$ mkdir state
$ dbt parse
$ mv target/manifest.json state/

If I change just the yaml to data_type: string:

$ dbt ls -s state:modified --state state/
19:17:06  Found 1 model, 0 tests, 0 snapshots, 1 analysis, 522 macros, 0 operations, 1 seed file, 0 sources, 0 exposures, 0 metrics, 0 groups
19:17:06  Running with dbt=1.5.0-b5
...
dbt.exceptions.ModelContractError: Contract Error in model my_model (models/my_model.sql)
  There is a breaking change in the model contract because column definitions have changed; you may need to create a new version. See: https://docs.getdbt.com/docs/collaborate/publish/model-versions

But if I also change the model's SQL to select 1::text as id, such that the contract works again — but has still undergone a breaking change! — it's no longer being caught during the state:modified comparison:

$ dbt ls -s state:modified --state state/
19:17:26  Running with dbt=1.5.0-b5
19:17:26  Found 1 model, 0 tests, 0 snapshots, 1 analysis, 522 macros, 0 operations, 1 seed file, 0 sources, 0 exposures, 0 metrics, 0 groups
test.my_model

If I had to take a wild guess, this is because the model is first selected on the basis of the change to its body, before we get to the same_contract comparison?

---

If I had my druthers / as a UX improvement, the ModelContractError message would also make clear what in the contract changed (similar to #7209). In practice, the change would also be reflected in the git diff, which someone could inspect in order to understand the cause for the failing CI check.

[jtcohen6]

If I had to take a wild guess, this is because the model is first selected on the basis of the change to its body, before we get to the same_contract comparison?

Looks like yes:

dbt-core/core/dbt/contracts/graph/nodes.py

Lines 429 to 441 in 050161c

	def same_contents(self, old) -> bool:
	if old is None:
	return False
	return (
	self.same_body(old)
	and self.same_config(old)
	and self.same_persisted_description(old)
	and self.same_fqn(old)
	and self.same_database_representation(old)
	and self.same_contract(old)
	and True
	)

If I switch the order so that self.same_contract(old) comes first, before self.same_body(old), then I see the exception I was expecting:

dbt.exceptions.ModelContractError: Contract Error in model my_model (models/my_model.sql)
  There is a breaking change in the model contract because column definitions have changed; you may need to create a new version. See: https://docs.getdbt.com/docs/collaborate/publish/model-versions

Reason: As soon as same_body() returns False, Python doesn't evaluate the rest of the methods in the and'ed conditional. (Right?)