Questions about TRD OR 4WD actuation

Does the TRD use any vacuum actuated components to engage 4WD? My understanding is that the front axles turn all the time. The transfer case is engaged by a solenoid w/o any vacuum actuated components. Since the front driveshaft turns freely in 2WD, I am not sure what is happening in the front diff to engage the front shafts? I also understand the rear locker is solenoid actuated as well w/o any vacuum components. Is my understanding correct and how is front shaft engaged with front diff?

 

After doing further reading it appears the ADD system is vacuum actuated. But loss of vacuum would fail system to 2WD. If that’s true, I think that is good. On my son’s F-150 a loss of vacuum fails the system to 4WD, which means damage can occur to driveline if on pavement or forced to drive on pavement. If Tacoma with ADD was in 4 WD and suffered a vacuum leak, would the sleeves separate and put it back in 2WD? I suppose if that happened you could still have the transfer case turning front shaft (until disengaged with selector switch) but no power to wheels thru half-shafts.