This one is very easy for me. When I pass a pedestrian on my bicycle, and I have to do it within close proximity, I pass with minimum speed disparity. I never yell "ON YOUR LEFT." Many don't know what it means. It will confuse or startle some. I will say "I am easing around your left." I most often exchange cordialities as I pass.
LOTS of pedestrians have buds. Pedestrians in parks and on paths tend to have very low situational awareness. They are often in la-la land and in sightseeing mode. Armed with that knowledge, it is incumbent upon me to expect unpredictable behavior. The best mitigating measure for me is passing with minimal speed disparity and communicating when possible.
I have seen pedestrians do remarkably absent minded stuff. Headphones on, walking with the flow of bicycles on a 10 foot wide path, wheel around and do a 180 without so much as a glance over the shoulder. Pedestrians cutting across paths without looking. Pedestrians with dogs on leashes taking up the entire path. One day I watches as an apparently homeless guy was walking on the levee path batture at an angle toward the path. Across the path in the direction he was walking was a street. I suspected he was going to connect to that street. I also saw a guy and gal cyclist riding on the levee path from the pedestrians blind side at a speed that would have them arriving at the same place at the same time. My wife and I were riding behind them. I could see it developing. Had I been the other cyclists, I would have slowed. They didn't and the pedestrian walked right into the path without looking.
Pedestrians do stupid stuff. Cyclists do stupid stuff. Motorists do stupid stuff. Situational awareness and a defensive posture are helpful.
Pedestrians always have the right away when I ride on shared trails. You should always slow way down passing a pedestrianor go ride on the highways and deal with traffic
