As an English speaker I imagine that it is possible that there are a whole host of French victories where this kind of chivalric enthusiasm carried the day, but I am not aware of them

There were indeed many. The reason they aren't as remember as battles like Nicopolis or Agincourt is because they were seen as so unremarkable; heavy cavalry - especially French heavy cavalry - held an exulted and much respected position in medieval Europe, and heavy cavalry in general was often the deciding factor in most battles - this only started to change in the mid-to-late 15th century as infantry became increasingly more professional, well-equipped and well-trained.

I know the French eventually won the hundred years war, but my understanding of this relates to Joan of Arc and some sort of revitalization of popular support

Not really, no. Joan of Arc had very little effect on the overall French war effort; the French made major gains both before and after her thanks to the competent professional generals employed by the French government, most of whom were nobility, as well as France's enormous advantage in manpower over the English. Remember that the French failed to retake Paris when Joan was present with the army - it was finally retaken after her death.

Eventual French victory in the war was inevitable; France's vastly larger population all but ensured this. The only reason the English had made such dramatic gains in the 1350s-60s and later the 1410s-20s is because they were embroiled in huge and devastating civil wars, first with Navarre and then with Burgundy. As soon as these civil wars were over, the French made a rapid comeback and retook lost land. The English simply didn't have the resources to sustain such a long war of attrition, no matter what short-term victories they achieved.

Conversely, in the build up to Agincourt the French army had the opportunity to attack the English force on a number of occasions but deferred and waited for their host to grow in size. If their arrogance was so great why did they hesitate to give battle before Agincourt?

The reputation of the English armies was very high, even after decades of setbacks in the 1370s-90s. The legacy of Crecy and Poitiers still lingered, as revealed in many contemporary written records. Following these crushing defeats, King Charles V had made it the general doctrine to avoid pitched battles with the English at all costs, unless the French had a huge numerical advantage. This strategy worked - the English armies were excellent in pitched battles but not in sieges, and when the French constantly took shelter behind city walls they were usually safe and could not be dislodged. This doctrine had continued all the way to 1415, and informed the military strategy of the French commanders. Additionally, Henry V already had a fearful military reputation, due to his victories in Wales and at Harfleur. The French also weren't in much of a hurry - they had the distinct advantage of fighting on home soil with a larger recruitable population, and they had managed to cut off Henry's line of retreat to Calais. Several of the wiser commanders saw no harm in waiting for reinforcements.

My best guess is that this jockeying for the vanguard was some sort of internal French cultural or societal mechanic. For a French knight or Noble was this sort of consideration, to be the first into battle, essential to maintaining their power at home and in court?

This is the general gist of it. The code of warrior honour was extremely strong in the French nobility (i.e. the ones that made up the heavy cavalry, and the first to charge into battle), even by the standards of the era. They had complete and utter contempt for infantry, and did not want them to get the credit for victory over the English; they essentially wanted to get in there and score a dazzling success before anyone else, to bolster their own prestige/egos and to reaffirm their status as valiant knights and warriors. This mindset was not universally shared - the infantry did not hold the same views, and several French commanders present did not either. Unfortunately the ones that wanted to wait for reinforcements and not charge straight in were labeled as cowards and traitors, as was apt to happen in the medieval era (literally the exact same reason why King Guy marched into the desert towards Saladin at Hattin in 1187), and they were overruled by the more zealous commanders that gave in to the demands of the knights. Arguably the single greatest problem with the French army at Agincourt was the lack of unitary command, as neither the King nor the Dauphin were present, i.e. the two highest ranking nobles in France, who could overrule anyone else. As always, the division of command led to problems. Henry V obviously faced no such problem, and had total command of his army and its strategy and tactics.

Sources: The Hundred Years War, volumes I-IV by Jonathan Sumption; 1415: Henry V's Year of Glory by Ian Mortimer

Thank you for your excellent follow up response!