When using ali-oss as STORAGE_VENDOR, the `put()` method treats string
body as a file path and calls `fs.statSync()` on it. Passing `'ok'`
causes `ENOENT: no such file or directory, stat 'ok'` during
instrumentation-check, crashing the server on startup.
Using `Buffer.from('ok')` ensures all adapters (aws-s3, minio, cos, oss)
handle the body as content rather than a file path.
