Test the connection: write a small file with the stored keys.

Organization admins, signed in. Answers 200 whether or not the write worked; test.ok says which, with the bucket's error code. Behind the warehouseExport flag (and the organizations flag): 404 not_found until it is on for your organization. Each run writes JSON lines under <prefix><dataset>/dt=<date>/<run>-<n>.jsonl and then a manifest at <prefix>manifests/<time>-<run>.json listing the files, their rows and SHA-256; load the files a manifest lists (a file with no manifest is from a run that failed and is written again). Parquet is not written. Keys are stored encrypted and never returned.