Fixed ===== - GridFS storage now maps a duplicate-key write error (MongoDB error code 11000) to HTTP 409 instead of letting it propagate as a 500. When two uploads of the same (deviceId, measurementId, fileType) raced past the isStored pre-check, both reached the store path and the unique fs.files index rejected the second insert; clients treated the resulting 500 as a retry rather than as "already stored" ([STAD-916])