Add bounded stdin to owner execution

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a06def-6490-7033-8448-2eab2d12ed44

docs/runbooks/profile-bwrap-local.md

@@ -61,6 +61,7 @@ Call `POST /v1/sandboxes/SANDBOX_ID/exec` with a bearer token and this body:
     "run_id": "run-456"
   },
   "credential_route_refs": [],
+  "stdin_text": null,
   "timeout_seconds": 30,
   "max_output_bytes": 65536
 }
@@ -68,6 +69,7 @@ Call `POST /v1/sandboxes/SANDBOX_ID/exec` with a bearer token and this body:
 
 The bearer authenticates access to the owner service; exact consumer identity
 matching additionally binds the command to the existing sandbox grant.
+`stdin_text` is capped at 1,000,000 UTF-8 bytes and is not returned or logged.
 
 ## Destroy