Short version: No success removing LH fork cap.

Valkpilot to the rescue with an extra pair of forks!
Long version: Before escalating, I gave the pipe / strap wrench approach one more session, this time with 2 strap wrenches, with the only tangible result being a broken strap wrench. Next, I gave the cap an overnight dose of PB Blaster. I didn't think it would help, but it couldn't hurt. Next, I cut a slot in the rounded head and used the impact blade. (I learned it's actually a steering linkage adjustment tool.) It's not really impact duty, but it is certainly harder than the fork cap.

No good luck.
Next, I drilled two half-inch deep F bit holes, tapped them with a 5/16" - 18 tap, ran two bolts in, placed the fork in a vice wrapped in a rubber mat (really big strap wrench)and put the 24" pipe wrench on them. I used constant and momentary pressure with the only tangible result being a bent 5/16" bolt. Then, I broke out the heat gun.

No good luck.
At this point, I believe the threads are galled. Even if I were to eventually remove the cap, I'm almost certain the tube will not be useable. Sad to know that careless reassembly has claimed another good part.