The _build_member_response helper tried to access member.user.preferred_name
but User model has no preferred_name field (it's on Settings). With lazy="raise"
this caused a 500 on GET /shared-calendars/{id}/members. Reverted to None —
the list_members endpoint already patches preferred_name from Settings.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>