I found the problem. Amazingly it's Firefox.
Firefox claims that the content is encoded, but then doesn't actually save it encoded:
"content": {
"mimeType": "application/vnd.mozilla.json.view; charset=utf-8",
"size": 18755,
"encoding": "base64",
"text": "{\"config\":{\"server\":{\"port\":3000,\"basePath\":\"\"},...snip
It should be more like:
"content" : {
"size" : 18755,
"compression" : 0,
"mimeType" : "application/json; charset=utf-8",
"encoding" : "base64"
"text" : "eyJjb25maWciOnsic2VydmVyIjp7InBvcnQiOjMwMDAsImJhc2VQYXRoIjoiIn0sImFwcGxpY2F0aW9uIjp7ImRvb...snip
},