devcontainer vscode settings not taking effect in remote container

• VSCode Version: 1.71.0 (Universal)
• Local OS Version: macOS Monterey 12.5.1
• Local chip architecture: Apple Silicon
• Reproduces in: Remote - Containers

Maybe I'm not understanding how this is supposed to work . . .

I have a devcontainer.json to which I added some settings:

  "customizations": {
    "vscode": {
      "extensions": [...deleted for brevity...],
      "settings": {
        "rubyTestExplorer.testFramework": "rspec",
        "rubyTestExplorer.logpanel": true,
        "rubyTestExplorer.debugCommand": "rdebug-ide",
        "rubyTestExplorer.filePattern": [
          "*_spec.rb"
        ]
      }
    }

After rebuilding the devcontainer and restarting VSCode I'd expect these settings to be present in my remote container but they are not:

> cat ~/.vscode-server/data/Machine
{}