hook_entity_type_alter function leads to infinite loop

Should this be reopened?

I think it's really a duplicate of #2924075: Plugin discovery hooks and event subscribers can cause infinite loops → .

Maybe. That issue seems oriented towards trying to prevent the problem. I am thinking more of how to document it. I am just not sure if there is a way to describe what's happening. Maybe not in 100% of the cases, but would "don't load an entity in this hook" be accurate?

I am thinking more of how to document it

While that would be good, I'm not sure how we would document all the ways this hook could cause a site to break (e.g your initial problem with tempstore isn't obvious it's loading an entity). If we instead are able to detect these loops as per #8 we'd know something is broken upfront.