Looks ok at first glance (and without knowing Dart, so no idea if its accurate there)
Does Dart have a standard implementation that you could define build commands for? See for example `filetypes.Kotlin.conf`.
Technically the dart compiler can be called on individual source files, just like in Kotlin. But, the most popular use for dart is probably building mobile applications with Flutter. And that requires the running the build command at the project base folder and never directly at the file level.
For example, [this](https://github.com/flutter/packages/tree/main/packages/go_router/example) is the project base folder, whereas all the dart source files are under `lib`.
I know for Kotlin as well, a lot of times you don't directly invoke the build command on the individual file, but rather using a build system like maven and gradle and invoke it at the project base folder.
So I guess is there a preference to add these build commands anyway, although they aren't all that useful for the normal development workflow?