Leaking AT fluid after Head gasket replacement

Hi- I recently took my 2002 Subaru Forester in to have the head gasket replaced as I was getting a small leak of coolant (according to the mechanic I always go to and trust). He referred me to another shop to have the head gasket replaced. While the engine was out, I also agreed to have the timing belt and water pump replaced ( I plan on keeping this car awhile–it’s paid for and a great car!) The mechanic also noted a bad solenoid and replaced that too. I noticed some spots on my driveway and blamed a guy that was doing some work on my home. It turns out the leak is from my car. Today, at a stop light, the person in the car in front of me told me he noticed a significant leak coming from my car when I was on the freeway. When I got home, I had several drops of reddish fluid leaking from the under side, from the midline, just at and behind my front tires (sorry, I don’t know much about the names of parts!) It seems to be transmission fluid–I plan to take it back to the shop, but it’s Monday, I work all week and drive over 30 miles a day to and from work, school etc. Is it safe to drive? I don’t want to destroy my auto transmission. I checked the ATF fluid (cold) and it appears very full. Should I just not drive it or can it be just overfull? How dangerous is this?

Since the engine was out it’s possible that the front pump seal (also called a torque converter seal) could have been damaged during the engine removal and install.
Whenever an engine or transmission is out both the front pump seal AND the engine rear main seal should be replaced.
Unfortunately, this is not always done even by shops and in my opinion it’s a non-negotiable issue. They ALWAYS get replaced.

There are a couple of possibilities here.
One is that someone damaged the seal while having to wrestle the engine in and out.
Two is that sometimes when the engine is removed the torque converter may come partially off the splines on the transmission. (There are 3 sets of splines)
If the engine is reinstalled without making 100% sure the converter is fully seated on all splines it’s possible for the seal to be damaged when the bolts holding the engine to the transmission are tightened. This can force the converter to seat fully and damage the seal.
In the worst cases the converter or flex plate may be damaged.

My feeling is that you should not drive this car at all since another motorist pointed this leak out to you. There are 2 risks involved.
One is the distinct possibility of roasting a transmission.
Two is the possibility of a fire if the the transmission fluid ignites on a hot catalytic converter.

Just offhand, it sounds like the shop made an error based on what I related above. You should contact them and let them be on the hook for a tow and fixing it.

Follow up question. You mention head gasket (singular). Does this mean only one was replaced? This should NEVER be done. Always in pairs.
Pardon the post length; just trying to cover the bases.