Currently it seems like the preview expects to be invoked for a single project only. But inside IDEs, there might be multiple Flutter projects open.

It would be nice if there was a way to spawn the server once without being tied to a specific project, and then have the preview work based on the project of the active file (eg. if you switch between files in two different Flutter projects, the preview would reload between them).

We could handle this in the IDE by spawning a server-per-project and just changing the URL for the iframe, but it would either mean starting the servers lazily (and shutting them down) which makes them slower, or using more memory to keep multiple servers alive.

cc @bkonyi