So, at the end of my PT, I am now ~halfway through those eccentric calf lift thingies she gave me, and I have come to one particular conclusion: it's a good thing I went to an expert, i.e. PT, 'cause she figured my achilles tendons were loose and floppy from too much flexing in the past, so my muscles were screaming tight but I never lost any flexibility 'cause my tendons gave a long time ago. The calf stretches I was trying to help my suffering achilles were actually aggravating the problem by continuing to stretch/stress the tendons themselves, and not loosening my calves much at all.
The PT has had me focus on stretching my hamstrings, reducing their pull on the calves, so the calves are hopefully loosening up from the other end (in addition to the brutal manipulation of my calves she was doing, I mean; and focusing on keeping my heel at ~90 degree angle to shin unless there's a good reason).
I don't really have any assurance that my tendons will tighten back up again so I can more directly stretch the calves, so slow and steady it is for the foreseeable future. The eccentric calf lifts should strengthen some muscle(s) in my calves so they may take up some tendon slack, otherwise it's just wait and see.
I am going to try resuming running in Aug (after having cycled through the calf lifts w/ increasing weight and reps), 15 min every other day for... well, increase after 2 wks if I can keep it up that long. If I can keep it up, could be up to some 30 min runs by September.
All the while, I've maintained my minimal level of utility cycling, 60-90 miles/wk, so the injury hasn't completely crushed my lifestyle, like it could have. Just no weekend or lunchtime rides, or am or pm commute extensions. I no longer get achilles tension from biking home (even pretty vigorously). I ice my ankles more after the calf lifts than I do after bike rides.
So, some progress is happening, anyway.