[setr]

Going solely off your description of the scenario; couldn’t you trivially model any history (H,H) node as two nodes —> (A, H’) —-> (H’, H) —> (H, B), and have it be deterministic again

I’m essentially thinking of H’ as a write-ahead-log prefixing any node

[ronin_niron]

Yes, you can — that's effectively what "expanding" the chart looks like. With a parent of N children you need N target nodes (one per possible "last-active" child) with deep history the cardinality is the size of the subtree's leaf set, which is exponential in nesting depth. That's exactly the explosion flat FSMs hit when you compose them — and the reason Harel introduced H notation in the first place, to elide it. So determinism is recoverable, just at the cost of the very property state charts were designed to deliver.

[anuramat]

you forgot to replace the em dashes :^)