mRNA is the messenger, and what happens to it once the message is delivered is likely unimportant. The message is used to produce something that is designed and intended to remain indefinitely, if not permanently.
Yes T cell immunity. Just like what your body does with every other virus. Now you get the point. It stimulates your body to act like it was exposed to prevent sickness without getting sick
You do realize this is exactly what a virus does. Takes over your cell and pumps out RNA to replicate itself in tile the cell dies. Then your body creates antibodies to neutralize the infection. You guessed it through RNA. It leaves memory immunity.
It does not genetically modify you. It does not. Are new exposures dangerous. You are almost to understanding of why this works.