Materialize references for all eligible targets

docs/integrations/json-output.md

@@ -104,6 +104,9 @@ target stage, lane ID when present, slot name, origin type and URI, digest,
 media type, byte size, and binding source. Reference content is not written to
 durable output.
 
+Reference `stage` is `chunk`, `extract`, or `normalize`. `lane_id` is omitted
+for chunk references and present for extract and normalize references.
+
 When references are bound, the manifest section has this shape:
 
 ```json