WebAPKs check whether they need to be updated at startup and perform the update if one is needed without telling the user. Once the update is complete the WebAPK is killed.

From the user's perspective the WebAPK getting killed after an update is indistinguishable from a crash.

I tested this by making a WebAPK for

https://webapk-test.appspot.com/generated.html?name=Long%20Train%20%F0%9F%9A%82&short_name=Short%20Train%20%F0%9F%9A%8B&scope=%2F&display=standalone&orientation=&start_url=&theme_color=purple&background_color=teal&icons=icon_hexagon_256&icon_sizes=true&update=true&update_name=Long%20Train%20%F0%9F%9A%82%F0%9F%9A%82&update_short_name=Short%20Train%20%F0%9F%9A%8B%F0%9F%9A%8B&update_scope=%2F&update_display=standalone&update_orientation=&update_start_url=&update_theme_color=purple&update_background_color=teal&update_icons=icon_hexagon_256&update_icon_sizes=true&seed=356