- do PANs automatically re-connect everything, once noise is down again?
Sure. I don't see why it shouldn't?
- if yes, is it instant, or after some lag?
I don't see why there should be a delay here...?
As soon as noise is too high between the device and the device you use to connect to the matrix = not part of your PAN.
As soon as noise not too high between the device and the device you use to connect to the matrix = part of your PAN.
- if not, what is the action to create a PAN and add things to it?
Most people are typically always connected to the matrix through their commlink which mean they typically always have a PAN. To manually add or remove devices to your PAN (either networking them or slaving them) you would probably take the Change Device Mode Anytime Minor Action (if you have DNI) or the Use Simple Device Initiative Major Action (if you don't have DNI).
I'm think of the case where a solo decker uses the jam action to disrupt the opposition PAN
You might want to consider using the Tar Pit action here, lowering the Data Processing rating of the opposition's commlink to zero will prevent him from taking the Send Message matrix action (making a call or send a text etc)
without causing a temporary blackout that will affect everything in the vicinity, including your own comms, and
even if the target PAN is more than 100 meters away. Using the Fork program let you disable two PANs at once (without splitting the pool).
...but then needs to drop the jamming in order to do their own hacking. As soon as the jamming stops, is everyone protected again? Or is there a window that you can take advantage of?
Again, I don't see why there should be a delay here...
If there is noise, then you are affected by noise.
If there is no noise, then you are not affected by noise.