I don’t think I flushed the pot any more vigorously than usual, but the plastic chain snapped off at the flush valve:
Some rummaging in the Chain Locker produced a steel chain from a long-ago flush valve that snapped into place:
Despite what you may think, I do not enjoy fiddling with this stuff, so I locked the link in place with a dab of hot melt glue:
Having recently repaired the other pot in the house, perhaps they’ll stay fixed for a while. It could happen!
The Smell of Molten Projects in the Morning 
Those unwelded chains are the worst. I bet someday soon you’ll get a slight tangle in the chain thereby shortening it. A strong tug on the toilet handle spreads a link open and then the chain comes apart after a few more flushes. Curses ensue.
Nah, they’re a close second behind fragile plastic chains.
A pox on their collective backside for cheapnifying a simple chain so it no longer works.