Moves one account onto the listed strategies with no template, in one accounts transaction: each entry keeps the unstamped managed sleeve on its strategy that already has its sleeve_name, else the lowest-id one on its strategy that no other entry took, else creates one, and winds down every other managed sleeve and the default sleeve. Funding and unmanaged sleeves are untouched. The account's buffer cash is cleared in the same transaction, so a template's cash target does not outlive it. If the account has a template assignment it is unassigned first; that is a separate write, so if the switch then fails the account is left untemplated with its old sleeves, and repeating the request finishes the switch.