David 'Arsehole' Hansen wrote:

One way such systems can fail is if the arm breaks off. This risk is
controlled by not having arms generally not striking trainstops and
so not suffering the fatigue this involves. An arm at the front of
the train will only strike a trainstop on rare occasions.

The risk is so remote as to be of no concern. One of the benefits of
trip cocks is that they are a very simple system. Adding a system to
retract them would complicate the system, and probably increase the
chances of a wrong-side failure.

If there were any concern regarding this issue the simplest thing would
be to tell drivers to kick them out of the way during preparation.