One of the things that confused me about Dieppe is how it seems like Germany would’ve just launched a large counter offensive that would’ve overwhelmed the roughly 10,000 Allied soldiers even if a foothold was established. What were the Allied plans had they actually captured the beachhead? Were there large amounts of soldiers in Britain that were put on standby so they could swiftly reinforce a foothold? Did the Allied just plan on holding a small heavily fortified area and not immediately expand?
Dieppe was never intended as a permanent invasion of Europe. It was only ever planned as a 'raid', with the attacking forces to be withdrawn before the Wehrmacht could concentrate against them. The intention was to seize the flanks, land forces in the port, demolish installations and seize assets, and study the German response. The troops were to be out by the next morning.
Looking at the plan for Dieppe it is curious as to why it was undertaken: a major risk for little reward. But it was a learning exercise. The British had no real idea how difficult an opposed landing on a French port would be, but from Churchill down (remembering perhaps the flawed Gallipoli campaign of 1915) they were very wary. They were also under Soviet pressure to distract the Germans.
As it was Dieppe provided many key lessons that were used on D-Day: the specialised tanks of 79th Armoured Division were developed to ensure supporting tanks arrived with the first wave, could deal with concrete emplacements, and make it off the beach, the need for heavy-calibre, precise naval gunfire was recognised, and much was learned about the use of commandos.