Add Databricks Snowflake and MongoDB attribute stores

[longquanzheng]

Summary

• add Databricks and Snowflake Attribute Store dialects with startup schema validation and parameterized idempotent MERGE writes
• add a MongoDB Attribute Store using existing collections, Flow IDs as _id, partial BSON upserts, and field-level filtering
• preserve PostgreSQL/MySQL behavior while sharing SQL schema discovery, conversion, refresh, and lifecycle code
• add configuration, SQL contract, MongoDB integration, Temporal/Cadence workflow, CLI, CI, and bilingual documentation coverage
• make Attribute Sync integration label-gated in one workflow, so regular Server CI starts none of MySQL, PostgreSQL, or MongoDB

Rationale

Attribute Sync previously projected only into PostgreSQL and MySQL. Applications that use cloud warehouses or MongoDB needed a separate dual-write path. These backends keep Dex's existing asynchronous latest-state and at-least-once attempt semantics while making every destination write idempotent by Flow ID.

User impact

Server operators can configure databricks, snowflake, or mongodb stores without protobuf or SDK changes. SQL tables and MongoDB collections must already exist. Databricks and Snowflake require a logically unique string flowIdColumn; MongoDB writes one document per Flow. Dex does not create schemas, constraints, indexes, migrations, or automatic backfills.

Databricks and Snowflake are covered by local driver and SQL contract tests. This change does not claim live cloud warehouse wire-compatibility testing.

The Attribute Sync CI workflow contains independent relational and MongoDB jobs. A single ci:attribute-sync label runs attributeSyncIntegTests against MySQL/PostgreSQL and mongodbAttributeStoreIntegTests against MongoDB. Regular Server CI starts none of these databases.

Validation

• make -C server unitTests
• make -C cli test
• make -C server attributeSyncIntegTests
• make -C server mongodbAttributeStoreIntegTests
• make copyright-check
• cd docs && npm run check
• go mod tidy -diff in server and cli
• CI runner policy and actionlint validation for the Server and Attribute Sync workflows
• companion skill-dex-developer 0.9.0 package, source-fidelity, skill, Codex plugin, and Claude plugin validation
• all pull-request checks passing, including both label-gated Attribute Sync integration jobs

[codecov]

Codecov Report

❌ Patch coverage is 0.80645% with 861 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...erver/service/common/attributestore/sql_dialect.go	0.00%	349 Missing ⚠️
.../service/common/attributestore/value_conversion.go	0.00%	183 Missing ⚠️
server/service/common/attributestore/sql_store.go	0.00%	170 Missing ⚠️
...erver/service/common/attributestore/mongo_store.go	0.00%	127 Missing ⚠️
server/service/common/attributestore/manager.go	17.94%	31 Missing and 1 partial ⚠️

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