resharper-rider-plugin VS rd

Basically you need to start with https://github.com/JetBrains/resharper-rider-plugin and add your custom logic to the backend part. There's no documentation for the APIs, but you can look at the decompiled Rider assemblies to check how similar actions are implemented. This won't be easy, but should be doable. Ping me on JB discord if you need help. CLion plugins won't help, CLion uses a different C++ code engine.

Postfix templates work a bit differently in ReSharper and Rider (C#) than they do in IDEA. They are designed to be more context-specific to not clutter the completion list, so for instance, you won't get a .foreach suggestion when you're on an expression that can't be iterated. Depending on your specific use-case, source templates could be an alternative. There is also the possibility to write a plugin and implement a custom postfix template. Just let us know what you're after, and we might be able to help :-)

JetBrains certainly is not stranger to the idea: Rider is Resharper’s process talking to IDEA’s UI over rd protocol (https://github.com/JetBrains/rd), Fleet is protocol agnostics and supports different servers.

If I understood it right, ReSharper/Rider is based on an MVVMish architecture using this protocol between a „backend“ (C# language services) and the „frontend“ (IntelliJ-based IDE, VS).