I got nerd-sniped on this, because I actually hadn't heard that before and would be horrified if it were true. It took some non-trivial digging to even get down into the "well, what does foo->>'bar' even map to in C?" level. I for sure am not claiming certainty, but based merely on "getIthJsonbValueFromContainer"
<https://sourcegraph.com/github.com/postgres/postgres@REL_17_...> it does seem that they do palloc copies for at least some of the JSONB calls
Postgres does have infrastructure to avoid this in cases where the result is reused, and that's used in other places, e.g. array constructors / accessors. But not for jsonb at the moment.
