Webpack can't resolve '@theia/plugin' for theia extension

I have implemented an extension in theia, and in that extension I want to use theia.commands. So did

import * as theia from '@theia/plugin';

In my package.json, in de dependencies section I have included

"@theia/plugin": "latest",

Building (tsc) goes fine. However webpack fails with the following error:

ERROR in ../extensions/myext/lib/browser/myext.js
Module not found: Error: Can't resolve '@theia/plugin' in 'c:\work\temp\owntheia\frontend\extensions\myext\lib\browser'

It sounds quite stupid issue, but I have no idea what’s wrong here. Did I forget something? Hopes somebody can help me out. Thanks!

@hbank you cannot use the plugin API from a @theia extension.

Thank you for the quick response. This clarifies it.