Vacuum/visibility is busted

While stress testing Pavan's 2nd pass vacuum visibility patch, I realized that vacuum/visibility was busted.  But it wasn't his patch that busted it.  As far as I can tell, the bad commit was in the range 692079e5dcb331..168d3157032879

Since a run takes 12 to 24 hours, it will take a while to refine that interval.

I was testing using the framework explained here:

Except that I increased  JJ_torn_page to 8000, so that autovacuum has a chance to run to completion before each crash; and I turned off archive_mode as it was not relevant and caused annoying noise.  As far as I know, crashing is entirely irrelevant to the current problem, but I just used and adapted the framework I had at hand.

A tarball  of the data directory is available below, for those who would like to do a forensic inspection.  The table jjanes.public.foo is clearly in violation of its unique index.

Thanks for any help,

Jeff