operational-modes.md

@@ -18,6 +18,7 @@ sequenceDiagram;
   CASd ->> runner: StageTreeResponse(path)
   deactivate CASd
 activate runner
+runner ->> runner: Command
   runner ->> CASd: CaptureTreeRequest(path)
 deactivate runner
   activate CASd
@@ -60,10 +61,10 @@ sequenceDiagram;
   CAS ->> worker: BatchUpdateBlobsResponse(status)
   worker ->> RWAPI: Lease(action_digest, action_result_digest)
 ```
+In this scenario, the first `StageTreeRequest()` operation is in charge of setting up the chroot. Once the chroot is staged, another `StageTreeRequest()` sets up the source files inside it.
 
 Note: The `chroot` is assumed to be in the LocalCAS. The chroots supported are advertised using Platform Messages.
 
-
 `StageTree()` and `CaptureTree()` operations handling by `buildbox-casd`
 are described below.