Battle of Cannae: "double" envelopment?

Well, Hannibal was in no position to call an audible, figuratively or literally, he spent the battle in the Center fighting for his life. His Lt on the flanks might have, the Romans seemed completely surprised. Now, the Centurions at Pydna, certainly did call audibles when they saw gaps appearing.
I like the term. Going to use it now.

Ah yes, but it’s also perforce all front. As legendary Marine Chesty Puller is said to have quipped, “We’re surrounded ? Excellent. Now we can shoot at them from every direction”.

Not necessarily. The traditional phalanx strategy was to put the heaviest, best equipped troops on the right flank because a) due to the shield being worn on the left hand, the right flank was perforce the least protected so heavier troops would fare better there and b) hopefully better fighters would quickly dispatch the relatively weak units a more traditional opponent had there and then be able to roll up the entire line.

When you have absolute air superiority and outnumber the in Arty…
Somehow I suspect, the AVR; *Aeris vires Romana * were absent that day.

Which is another thing which caused problems against the *Exercitus Romanus

This quite correct. The bigger the battle the harder for the top commander to control and sometimes to even have any idea if they are winning or losing. The OP mentioned smoke/dust and noise interfering and he is quite right that this was also a terrible challenge for commanders.

Using horns or drums or colored flags would be used to send commands over distances. Also they might send a runner to carry a message. Unfortunately this runner could get lost, blown up, or lose his nerve and terribly often the messages didn’t get thru or came late and after the circumstances had drastically changed. Later when technology permitted other communication methods could be used like sending up colored flares or rockets. At least at the starting years of World War II radios were very often in short supply or unreliable and still generals often had little idea what was happening with their troops.

Most always a smart move for the general was to keep several battalions in reserve nearby under his control to use if the situation called for it.

Or as Bedford Forrest once say: “Charge 'em both ways!”

I somehow in my mind had the battle of Cannae being Alexander the Great vs. the Persians and was so sure about this I didn’t bother to look it up. I apparently conflated a whole bunch of different things I read, providing a very good example of just how bad human memory can be.