Stage uploads before accepting HTTP runs

docs/config.md

@@ -130,12 +130,15 @@ Accepted upload content types:
 - `application/gzip`
 - `application/x-gzip`
 
-Accepted uploads return:
+Accepted uploads return after the archive is staged and validated:
 
 ```json
 {"run_id":"<id>","status":"accepted"}
 ```
 
+Malformed tar or gzip content and invalid staged bundles are rejected before a
+run id is issued.
+
 The run id can be queried through `GET /runs/<run_id>` while the status record
 is retained in memory. Completed records expire after `server.http.retention`;
 expiration also removes committed staged bundle directories for completed