Azure Function Runtime ISO8601 datetime mangling

function.json

{
  "disabled": false,
  "tracing": {
    "consoleLevel": "verbose"
  },
  "bindings": [
    {
      "authLevel": "anonymous",
      "type": "httpTrigger",
      "direction": "in",
      "route": "test-ms",
      "methods": ["GET", "OPTIONS"],
      "name": "req"
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    }
  ]
}

index.js

module.exports = function(context, req) {
    // Set up a datetime at the "top of the second":
    context.res = {
        'test_time': '2026-04-20T00:00:00.000Z',
    };
    // Observe that no stringification functionality modifies the underlying datetime string:
    console.log(JSON.stringify(context.res));
    // Runtime outputs test_time with "2026-04-20T00:00:00Z", missing the milliseconds.
    context.done();
};