Flaky unit-test collection: KeyError importing feast.infra.mcp_servers.mcp_server under pytest -n #6633

Expected Behavior

make test-python-unit (pytest with -n / xdist) collects sdk/python/tests/unit/infra/feature_servers/test_mcp_server.py reliably.

Current Behavior

Intermittently, parallel unit-test collection fails on an xdist worker while importing the MCP server package, which aborts the whole session:

ERROR collecting tests/unit/infra/feature_servers/test_mcp_server.py
sdk/python/tests/unit/infra/feature_servers/test_mcp_server.py:8: in <module>
    from feast.infra.mcp_servers.mcp_config import McpFeatureServerConfig
sdk/python/feast/infra/mcp_servers/__init__.py:4: in <module>
    from .mcp_server import add_mcp_support_to_app
<frozen importlib._bootstrap>:946: in _load_unlocked
E   KeyError: 'feast.infra.mcp_servers.mcp_server'

The tests pass in isolation, so this surfaces as a flaky unit-test-python job failure (seen recently on unit-test-python (3.12, ubuntu-latest)).

Root cause: feast/infra/mcp_servers/mcp_server.py imports feast.feature_store.FeatureStore at module load but uses it only for a type annotation on add_mcp_support_to_app. Because the package __init__.py eagerly imports mcp_server, importing feast.infra.mcp_servers pulls in the whole feature_store import graph. Under parallel collection that heavy import races with an in-progress feature_store import; the partially-initialized mcp_server module is cleaned up, and the outer import's sys.modules.pop("feast.infra.mcp_servers.mcp_server") raises KeyError.

Steps to reproduce

Ordering-dependent, so not reliably reproducible in isolation; it surfaces under the full parallel unit-test run (make test-python-unit, pytest -n). Isolated collection (pytest --collect-only .../test_mcp_server.py) always succeeds.

Specifications

• Version: master (module unchanged through 0.65.x)
• Platform: CI unit-test-python (3.12, ubuntu-latest)
• Subsystem: infra/mcp_servers, unit-test collection

Possible Solution

Move the FeatureStore import in mcp_server.py under TYPE_CHECKING (it is only a type annotation), so importing mcp_server no longer drags in the feature_store graph. I have a fix ready and will open a PR referencing this issue.