Not sure why you think they can shitcan them at literally any moment. Although GCP's track record of deprecation is of course far worse than AWS's, they do make and adhere to promises in their terms of service that, in most cases, they will give at least 12 months before deprecating services which have reached general availability. This includes both App Engine and Cloud Run, minus any features that have not yet reached general availability and minus one very fair documented exception for App Engine.
Details:
https://cloud.google.com/terms/deprecation
https://cloud.google.com/terms <-- search for "Discontinuation of Services"
Disclosure: I used to work for Google, including the GCP team, but I haven't worked for Google in over 5 years and am not speaking for Google here.