Document subprocess run results

docs/integrations/json-output.md

@@ -12,6 +12,10 @@ All paths below are logical, relative, slash-separated bundle paths. The
 encoder always emits the first four JSON files below and adds lane or chunk-map
 files when their corresponding artifacts are available:
 
+A subprocess caller first obtains the physical bundle root from the
+[run-result receipt](run-result.md), then resolves `index.json` beneath that
+root for the logical discovery described here.
+
 | Path | Purpose |
 | --- | --- |
 | `index.json` | Entry point that names the other published files and lane payloads. |