Remove LocalBackend from root exports

[Kovbo]

Summary

• remove LocalBackend from the root art.__all__ export list
• update the stale LangGraph docs snippet to import LocalBackend from art.local
• add an import-boundary regression test for root art imports and star imports

Context

LocalBackend was intentionally removed from eager root imports in #548 so lightweight import art does not pull backend-only dependencies. This keeps that behavior explicit instead of reintroducing a top-level art.LocalBackend export.

Alternative to #642.

Test plan

• uv run pytest tests/unit/test_model_support_import_boundary.py
• uv run ruff check src/art/__init__.py tests/unit/test_model_support_import_boundary.py
• manual uv run python check that LocalBackend is absent from art.__all__, absent from from art import *, and art.local is not loaded

[mintlify]

Preview deployment for your docs. Learn more about Mintlify Previews.

Project	Status	Preview	Updated (UTC)
openpipe-art	🟢 Ready	View Preview	Jun 4, 2026, 9:54 PM

💡 Tip: Enable Workflows to automatically generate PRs for you.