Every place a request's history breaks the provider contract: an assistant call turn whose calls
are not ALL answered by the run of tool turns directly after it (consecutive tool turns are one
provider message on every driver). Empty when the history is valid.
Every place a request's history breaks the provider contract: an assistant call turn whose calls are not ALL answered by the run of tool turns directly after it (consecutive tool turns are one provider message on every driver). Empty when the history is valid.