The frontend_server currently communicates with tooling using a text-based protocol over stdin/stdout.

This makes evolving the API with a soft-transition difficult. For example, the hard transition needed to move past flutter/engine#42568, would probably have been fine by itself, but it happened to land during a week with two other roll-blockers in the Dart SDK.

We could reduce the risk of roll-blockers in this area by migrating the frontend_server to an easier-to-evolve RPC protocol over a socket, for example, but I'm sure there are also other solutions in this space.

cc @eyebrowsoffire @aam FYI @christopherfujino