feat: add v2 catalog schema support to snowflake/bigquery adapters

[aahel]

Problem

Implementing the catalogs.yml v2 spec requires per-(catalog_type, platform) config schemas (e.g. HorizonSnowflakeConfig, LinkedSnowflakeConfig, BiglakeMetastoreBigqueryConfig). Those schemas describe adapter-specific knowledge — Snowflake's external_volume semantics, BigQuery's gs:// requirements, etc. — and should live with the adapter that owns them, not in dbt-core. dbt-core needs a way to validate v2 catalogs.yml at parse time without knowing about adapter-specific schemas.

Solution

Each adapter declares its v2 catalog schemas as a CATALOG_V2_CONFIGS class attribute on the adapter class — mirroring the existing CATALOG_INTEGRATIONS pattern that already exists for v1 catalog integrations:

# dbt-snowflake/src/dbt/adapters/snowflake/impl.py
class SnowflakeAdapter(SQLAdapter):
    CATALOG_INTEGRATIONS = [...]                     # v1 (existing)
    CATALOG_V2_CONFIGS = {                           # v2 (new)
        "horizon": HorizonSnowflakeConfig,
        "glue": LinkedSnowflakeConfig,
        "iceberg_rest": LinkedSnowflakeConfig,
        "unity": LinkedSnowflakeConfig,
    }

dbt-core looks up via adapter_class.CATALOG_V2_CONFIGS.get(catalog_type) at parse time. Schemas are dbtClassMixin dataclasses, so cls.validate() handles structural checks (unknown keys, required fields, types) via jsonschema and __post_init__ covers semantic constraints (value ranges, enum values, cross-field rules).

Architecture

• BaseAdapter.CATALOG_V2_CONFIGS: Dict[str, Type[dbtClassMixin]] = {} — empty default; adapter subclasses override
• Schema definitions live with their owning adapter package (dbt-snowflake, dbt-bigquery)
• dbt-core never imports specific platform configs; it only walks adapter_class.CATALOG_V2_CONFIGS
• Declarative on the adapter class — no global registry, no side-effect imports, no order-sensitive registration

This is the first of three coordinated PRs:

1. This PR: base + snowflake + bigquery
2. dbt-core PR: v2 framework that consumes CATALOG_V2_CONFIGS for platform validation
3. dbt-databricks PR: declare UnityDatabricksConfig, HiveMetastoreDatabricksConfig on the Databricks adapter

Files changed

• dbt-adapters/src/dbt/adapters/base/impl.py — add CATALOG_V2_CONFIGS class attribute (empty default)
• dbt-snowflake/src/dbt/adapters/snowflake/catalogs/_v2.py (new) — HorizonSnowflakeConfig, LinkedSnowflakeConfig
• dbt-snowflake/src/dbt/adapters/snowflake/impl.py — declare CATALOG_V2_CONFIGS
• dbt-bigquery/src/dbt/adapters/bigquery/catalogs/_v2.py (new) — BiglakeMetastoreBigqueryConfig
• dbt-bigquery/src/dbt/adapters/bigquery/impl.py — declare CATALOG_V2_CONFIGS
• 24 unit tests (16 snowflake + 8 bigquery) covering schema validation and class-attribute registration

Note on commits

The first three commits (3db4ac99, e63f0001, 68621df5) explored a global registry pattern (register_catalog_config() / get_catalog_config()); the fourth commit (18e534cf) refactors to the class-attribute pattern after recognizing it aligns better with the existing CATALOG_INTEGRATIONS convention. Final design at HEAD is cleaner; happy to squash before merge if preferred.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

[QMalcolm]

Looks good to me!

[Copilot]

Pull request overview

Adds adapter-owned CATALOG_V2_CONFIGS schema registration so Snowflake and BigQuery can expose catalogs.yml v2 validation metadata without dbt-core importing adapter-specific config classes.

Changes:

• Adds BaseAdapter.CATALOG_V2_CONFIGS as the shared extension point for v2 catalog config schemas.
• Introduces new Snowflake and BigQuery v2 config dataclasses and registers them on each adapter.
• Adds unit tests plus changelog entries for the new schema-registration surface.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
dbt-snowflake/tests/unit/test_v2_catalog_configs.py	Adds unit tests for Snowflake v2 config registration and validation helpers.
dbt-snowflake/src/dbt/adapters/snowflake/impl.py	Registers Snowflake v2 catalog config classes on the adapter.
dbt-snowflake/src/dbt/adapters/snowflake/catalogs/_v2.py	Defines new Snowflake v2 config dataclasses and semantic validation.
dbt-snowflake/src/dbt/adapters/snowflake/catalogs/__init__.py	Re-exports the new Snowflake v2 config classes.
dbt-snowflake/.changes/unreleased/Features-20260429-231718.yaml	Adds Snowflake changelog entry for the feature.
dbt-bigquery/tests/unit/test_v2_catalog_configs.py	Adds unit tests for BigQuery v2 config registration and validation helpers.
dbt-bigquery/src/dbt/adapters/bigquery/impl.py	Registers the BigQuery v2 catalog config class on the adapter.
dbt-bigquery/src/dbt/adapters/bigquery/catalogs/_v2.py	Defines the BigQuery v2 config dataclass and semantic validation.
dbt-bigquery/src/dbt/adapters/bigquery/catalogs/__init__.py	Re-exports the new BigQuery v2 config class.
dbt-bigquery/.changes/unreleased/Features-20260429-231718.yaml	Adds BigQuery changelog entry for the feature.
dbt-adapters/src/dbt/adapters/base/impl.py	Adds the base adapter hook for v2 catalog schema registration.
dbt-adapters/.changes/unreleased/Features-20260429-231718.yaml	Adds dbt-adapters changelog entry for the new extension point.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.