Update:
The local NAPA shop was able to get me the parts overnight from their warehouse. NAPA "Adaptive One" polymer coated rotors, NAPA rebuilt calipers (one the TRW/Land Rover body), and the OEM TRW pads. Maybe not my preferreds, but "in stock" is golden.
With the parts in hand I pulled apart the right front brake assembly. The caliper was locked so tight on the disc that I had to use a pry bar to get it off. The top caliper pin was pretty well jammed with no wiggle. Took several hard tugs to get it out. The bottom pin had a little wiggle but still pretty stiff.
With the caliper hanging from a wire and still attached to the brake hose I put on a C-clamp and tried to push in the pistons. Even with reservoir cracked open, couldn't get the pistons to budge under the clamp. Then I tried again with the bleeder valve open. If the line were clogged or a problem at the booster/master, then an open bleeder ought to mitigate. Even with the bleeder open still could not get the pistons to budge. Took the caliper off and laid it on the bench without a banjo bolt installed. Still frozen.
Put on the new parts both sides and bled the front brakes. Had no issues running fluid into the caliper from the master. In fact it flowed by gravity. Test drove it and it feels good (in fact better than before this issue arose). All rotors at normal operating temperature (under 100 degrees) even after a freeway drive.
So seems obvious the mechanics claim of defective booster and master was bogus. Offering an $1800 brake system repair to replace a $150 rebuilt caliper. I recorded videos of my efforts to free the frozen caliper. Trying to decide what to do with them. Facebook, YouTube, Yelp?
Waterboy787: What's this about electronically resetting the brakes? Anyone else know of that? I have a Fox scanner device. Could I do it with that?
Thanks to everyone for your thoughts and advise. Much appreciated!