> What happens to it up the callstack?

as they say in the post, these files get generated every 5 minutes and rolled out across their fleet.

so in this case, the thing farther up the callstack is a "watch for updated files and ingest them" component.

that component, when it receives the error, can simply continue using the existing file it loaded 5 minutes earlier.

and then it can increment a Prometheus metric (or similar) representing "count of errors from attempting to load the definition file". that metric should be zero in normal conditions, so it's easy to write an alert rule to notify the appropriate team that the definitions are broken in some way.

that's not a complete solution - in particular it doesn't necessarily solve the problem of needing to scale up the fleet, because freshly-started instances won't have a "previous good" definition file loaded. but it does allow for the existing instances to fail gracefully into a degraded state.

in my experience, on a large enough system, "this could never happen, so if it does it's fine to just crash" is almost always better served by a metric for "count of how many times a thing that could never happen has happened" and a corresponding "that should happen zero times" alert rule.