Plan a group SPLIT for the live day: given who goes in which subgroup (and optionally where each subgroup is), returns p

Plan a group SPLIT for the live day: given who goes in which subgroup (and optionally where each subgroup is), returns per-subgroup allowed/blocked saved places (each subgroup constrained only by its OWN members' stated no-gos from trip_member_prefs), the reconvene anchor (the day's next locked/protected stop), and a leave-by per subgroup with a 15-min margin. Travel is a walking estimate from straight-line distance unless you pass travelMinutesToAnchor. Read-only; writes nothing.