What if a project has a plugin architecture and plugins are compiled files that can be dropped in at runtime? Those plugins can be any license then, is it not?
Plug-ins are generally considered a derived work, if directly written to use a specific API. You would need to build a module that works for many different systems and only uses the Plane APIs as a shim.
Even then, the shim might be argued to be infected, and thus the rest of the module too. In that case, you still could be facing an expensive and risky lawsuit, because I don’t think there are any precedents to predict how those winds will blow.
No. Those plugins call functions from AGPL's codebase and they are designed only to be combined with AGPL's work into a larger work, so they are derivative works.
But there is a chance that CSS and svg icons are not required to be GPL.
Even then, the shim might be argued to be infected, and thus the rest of the module too. In that case, you still could be facing an expensive and risky lawsuit, because I don’t think there are any precedents to predict how those winds will blow.