Right-click a folder (or file) in the Explorer → New C# File → Class / Interface / Enum / Record / Struct.
The namespace is auto-computed from the nearest .csproj (using its RootNamespace if set, otherwise the project file name) plus the folder path relative to it. Falls back to the workspace folder name if no .csproj is found.
csharpdevextensions.fileScopedNamespace(defaulttrue) — use file-scoped (namespace Foo;) vs block-scoped (namespace Foo { ... }) namespaces.
npm install
npm run watchPress F5 in VS Code to launch an Extension Development Host with the extension loaded.