I am developing a VSCode extension with a webview. Inside this webview I run a script bundle.js that originates from a number of TypeScript sources bundled up with webpack. The script is loaded via a vscode-resource URI. The respective source map file bundle.js.map lies right next to it in the file system.
Now when I start my extension from a host VS Code in debug mode and use "Developer: Open Webview Developer Tools" I see the bundle.js only, with a hint, that there are source maps. But the respective TS sources don't appear in the navigator and cannot be loaded using CMD-P. Adding the source map by hand (right-click > Add source map...) doesn't have any effect, neither with a vscode-resource URI nor with a file URI.
When I use the webview's HTML as a file in Chrome directly but with a relative URL to load the very same script, I see all sources nicely in the Chrome Debugger.
How can I convince the Webview Dev Tools to use the source maps of the scripts it runs?