[AlexeyShalaev]

Fixes #78.

import sqlalchemy_foundation_kit failed on SQLAlchemy 2.1, which the metadata (sqlalchemy[asyncio]>=2.0.35,<3.0.0) lets every fresh install pick: base/engine.py imported FallbackAsyncAdaptedQueuePool, and SQLAlchemy 2.1 removed it together with the async_fallback mode it served.

Change

• base/engine.py registers fallback_async_adapted_queue only when sqlalchemy.pool still has the class (SQLAlchemy 2.0). On 2.1 the kit imports, the five other built-ins resolve as before, and resolving fallback_async_adapted_queue raises the registry's usual ValueError with the list of available pools. Nothing changes on SQLAlchemy 2.0.
• A regression test imports the engine module in a fresh interpreter after removing the class from sqlalchemy.pool, the way 2.1 looks to the kit. It fails on master with the ImportError from the issue and passes with the change.
• The tests that exercise the fallback pool itself are skipped where SQLAlchemy no longer has it, instead of breaking the whole module at import.
• CI gets a job, All tests (newest SQLAlchemy), that runs uv lock --upgrade-package sqlalchemy and the whole suite, so the next SQLAlchemy release that breaks the kit shows up in CI rather than in a user's install. It is part of All checks passed. uv.lock stays on 2.0.49, so the existing jobs keep testing 2.0.
• docs/agents.md and the PoolSettings docstring say that fallback_async_adapted_queue exists only on SQLAlchemy 2.0.

Checks run locally

• uv run ruff check ., uv run ruff format --check ., uv run mypy sqlalchemy_foundation_kit: clean; pre-commit on the changed files: passed.
• The regression test on master: fails with ImportError: cannot import name 'FallbackAsyncAdaptedQueuePool' from 'sqlalchemy.pool'; with the change it passes.
• Whole suite on the locked SQLAlchemy 2.0.49 with coverage (uv run pytest --cov=sqlalchemy_foundation_kit --cov-fail-under=90): 665 passed, coverage 94.24%.
• Whole suite on SQLAlchemy 2.1.6 (uv run --with "sqlalchemy[asyncio]==2.1.6" pytest, integration tests on postgres:17-alpine included): 662 passed, 3 skipped. The three skipped tests are the ones that exercise FallbackAsyncAdaptedQueuePool itself.
• uv lock --upgrade-package sqlalchemy, the new CI job's first step, resolves 2.1.6 (uv.lock was restored afterwards and is not part of this change).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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