A’ye, sir. You are correct! My 15/16 wrench most definitely snuggles that 24mm bolt more so than any 24mm tool I’ve set on it. I’ve managed not to round the corners in my many, many attempts and the many, many slip-offs under wrenching load. A breaker/cheater bar isn’t a tool option for this job anyway, so I have no concern about any negative consequences that might result from using one.
Moving forward, my plan is this:
I ordered a ratchet extension drive bar–a tool purpose-built for my exact dilemma. I’m going to attach a 1/2-in wobble to it, and a 1/2-in 15/16-in shallow 6pt to the wobble. If this doesn’t work, then I will (tentatively) bail on that accursed fastener and remove the air plenum from the top of the engine with the hope that its absence will allow access to that part that I ACTUALLY NEED to work on!