SwNtfy Fn 0004H: Session Is Now Active

  Expect: AX    0003H
          BX    ID of the session that is now active
          CX    flags: 0001H=this is a new session
                       0000H=resuming a previously-suspended session
          ES:DI addr of switcher's service-entry address
  Return: AX    0000H (you must return 0 in all cases)
    Info: Task switchers call this to let you know that a new session has
          been started or that a suspended session has been resumed.

          When called, interrupts are enabled you may use all DOS fns.

       BX will contain the session ID of the session that has been

    ES:SI will contain the task switcher's service entry address.  Use this
          address if you need to call any task switcher service fns.

  Return: AX=0000H (must be 0)

See Also: Switcher Services and Notifications
          INT 2fH 4bxxH (switcher functions)