Hi there and welcome. The mantra with bronchiectasis is 'if you don't use it you lose it'
I have had bronchiectasis since I was 3 and am now 64. When I was six we found a wonderful consultant whose methods were considered to be way off the wall. antibiotics given through oxygen, (nebulised) physio to teach me to breathe and get the gunk up and exercise exercise exercise. I was marched up cliff paths, forced on to netball pitches and thrown into swimming poole. How I hated those ashma kids who were allowed to sit out of games sessios.
result, a normal life despite extensive area of bronchiectasis. Given that treatment for bronchiectasis is still not what it should be owing to governmental and medical emphasis on copd ( they get the money) looking after yourself is very important.
Yourbronchiectasis did not begin on the day that you were diagnosed with it. you had probably been living and running with it for years.
Listen to your body. If you have an exacerbation and need to take antibiotics lay off the running. Bronchiectasis can make you very debilitated so it is important to get the balance between keeping it working and being kind to yourself when needed.
Good luck, I am sure that you will be fine and happy running!