delete_session/delete_sessions cascade-delete delegate children, but the
write-guard check only looked at the root. A guarded delegate child could be
removed out from under its live turn, and in bulk delete an active id that
was also another selected root's delegate child was reported in
skipped_active while the cascade deleted it anyway.
Check {root, *delegate children} via a small _guarded_ids helper: single
delete refuses, bulk delete skips the root, so the cascade never touches a
guarded row. Ports the delegate-protection idea from #124496.
Co-authored-by: JoaoMarcos44 <joaomarcosdias444@gmail.com>
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