No ObjectScript button in the VSCode activity bar

I've just installed Visual Studio Code, installed the InterSystems ObjectScript Extension Pack as documented here, connected it to a local InterSystems IRIS instance, and created a workspace associated with one of that instance's namespaces. However, after doing this, I don't see the ObjectScript button on the left toolbar when opening the workspace.

The ObjectScript extensions are installed and enabled as shown below; I've tried reinstalling them and restarting VSCode, but this doesn't make a difference:

Has anyone seen behavior like this before? I'd appreciate any suggestions for troubleshooting this.

edit: I've also right-clicked the sidebar and seen that I can toggle buttons on and off, but the ObjectScript button isn't shown as an option there.