Validate Distributor endpoints before publication

docs/integrations/distributor/api.md

@@ -8,8 +8,10 @@ and [operations guide](../../operations.md).
 
 ## Upload Admission
 
-Weatherreporter uses an absolute HTTP(S) endpoint as a base URL. The client
-posts a gzip-compressed source bundle to:
+Weatherreporter uses an absolute HTTP(S) endpoint with a host as a base URL.
+It allows a path prefix but rejects userinfo, query strings, and fragments
+before local report work begins. The client posts a gzip-compressed source
+bundle to:
 
 ```text
 POST /v1/pipelines/<pipeline_id>/upload