One plugin has @types/cesium as a dependency. Not only are they incorrect types - the package also has cesium as a dependency. Which means that the TerriaMap which imports the plugin will have terriajs-cesium and cesium in node_modules.
From a quick inspection of build JS files (for TerriaMap with given plugin) - I couldn't find any references to node_modules/cesium - but it could cause future problems.
How should a plugin get access to terriajs-cesium types?