Fix external DB manager upgrades with existing tables

[anmolxlight]

What

Fixes external DB manager upgrades when manager-owned tables already exist but the manager-specific Alembic version table does not.

Previously, BaseDBManager.upgradedb() treated that state as an empty database, called create_db_from_orm(), and stamped the manager to head. Because metadata.create_all() is a no-op for existing tables, migration bodies were skipped while Alembic believed the schema was current.

Why

This breaks upgrades such as Airflow 3.1 + edge3 1.x to Airflow 3.2 + edge3 3.4, where edge_job, edge_worker, and edge_logs already exist from the pre-EdgeDBManager era, but alembic_version_edge3 does not. The old path stamped edge3 to head without applying migrations that add columns like edge_worker.concurrency and edge_job.team_name.

How

• Detect existing manager-owned tables before falling back to ORM creation in BaseDBManager.upgradedb().
• If tables exist with no manager revision, stamp the manager to its base revision, then run Alembic upgrade to heads.
• Apply the same behavior to FABDBManager.upgradedb(), which has its own upgrade implementation.
• Add generic BaseDBManager tests plus edge3 and FAB coverage.

Tests

• uv run ruff check airflow-core/src/airflow/utils/db_manager.py airflow-core/tests/unit/utils/test_db_manager.py providers/edge3/tests/unit/edge3/models/test_db.py providers/fab/src/airflow/providers/fab/auth_manager/models/db.py providers/fab/tests/unit/fab/auth_manager/models/test_db.py
• uv run --project airflow-core pytest airflow-core/tests/unit/utils/test_db_manager.py -q
• uv run --project providers/edge3 pytest providers/edge3/tests/unit/edge3/models/test_db.py -q
• uv run --project providers/fab pytest providers/fab/tests/unit/fab/auth_manager/models/test_db.py -q

Fixes: #66524

[vincbeck]

LGTM but I'd like to have @jscheffl approval as well

[jscheffl]

In general GOOD! Thanks for the fix - actually ran into the same myself but had no time in discovering the root. But now seeing the PR this is opening my eyes!

Can you fix the nit?
Any maybe would be good to split the PRs such that we can make the airflow-core diff as backport into Airflow 3.2.2

[github-actions]

Hi maintainer, this PR was merged without a milestone set.
We've automatically set the milestone to Airflow 3.2.3 based on: backport label targeting v3-2-test
If this milestone is not correct, please update it to the appropriate milestone.

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[jscheffl]

@anmolxlight thanks for the patch!

As I requested to remove Providers I am not able to back-port such that it can get into 3.2.2. Are you planning to revamp another PR with the earlier proposed changes in providers? Would be great! (Alternatively I could but would leave the credit rather to you :-D)

[github-actions]

Backport successfully created: v3-2-test

Note: As of Merging PRs targeted for Airflow 3.X
the committer who merges the PR is responsible for backporting the PRs that are bug fixes (generally speaking) to the maintenance branches.

In matter of doubt please ask in #release-management Slack channel.

Status	Branch	Result
✅	v3-2-test

[anmolxlight]

Yes, I will open a separate provider-only PR restoring the edge3/FAB compatibility changes that were removed here. I will keep it scoped to providers and reference this PR for the core behavior.

[anmolxlight]

Opened the provider-only follow-up here: #66883. It restores the Edge3/FAB compatibility path only, with regression coverage for the existing-provider-tables/no-Alembic-version case.