Fix concurrent-session crash on GQL DataLoaders

[shangyian]

Summary

findNodesPaginated (and any GraphQL query whose resolution fires multiple DataLoaders concurrently) was intermittently failing with: This session is provisioning a new connection; concurrent operations are not permitted on a subset of edges.

The root cause was that get_context was unconditionally attaching its Depends(get_session) session to request.state.test_session, which session_context() then handed back to every DataLoader on the request. Concurrent DataLoaders sharing a single AsyncSession raced on connection acquisition; whichever lost raised the error. The original not hasattr(...) guard was a no-op since nothing upstream ever pre-attached the attribute.

The fix gates the attachment on app.dependency_overrides.get(get_session), where only tests register the overrides. In tests, the shared session is still attached so DataLoaders reuse the test transaction. In production, no attribute is set, so each DataLoader opens its own independent session via session_context().

Test Plan

Test coverage added for both code paths in test_main.py.

• PR has an associated issue: #
• make check passes
• make test shows 100% unit test coverage

Deployment Plan

[netlify]

✅ Deploy Preview for thriving-cassata-78ae72 canceled.

Name	Link
🔨 Latest commit	10d3b60
🔍 Latest deploy log	https://app.netlify.com/projects/thriving-cassata-78ae72/deploys/69ec6adbf843f80008103dd7