Fix issue where a detached relationship on RoleAssignment

[shangyian]

Summary

The bug: DJHTTPBearer and get_auth_context each get their own database session via Depends(get_session). The User is loaded with selectinload(role_assignments) in the bearer's session (S1), stored in request.state.user, then S1 closes, which expunges all its ORM objects, clearing the eagerly-loaded collection from the instance's state. When get_auth_context runs in session S2 and calls list(user.role_assignments), the User is detached and the collection is gone, triggering the lazy load error.

The fix is for get_effective_assignments to issue a fresh select for RoleAssignment filtered by user id using the current session. It never touches the detached relationship at all.

Test Plan

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

Deployment Plan

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