Add opt-in CLI execution report files

docs/integrations/subprocess.md

@@ -29,6 +29,13 @@ When using `--out`, the caller owns the output path, its permissions, and
 cleanup. Treat rendered prompts, generated artifacts, stdout, and stderr as
 potentially sensitive.
 
+For `run`, an optional [execution report file](../cli.md) contains terminal
+metadata separate from generated stdout or `--out`. The caller owns that
+path's permissions and retention. Output and report files are not a
+transaction: one may be written when the other fails, and a preexisting report
+may remain when the invocation has no terminal event. Check the exit status
+and diagnostics rather than assuming a report path contains this run's data.
+
 ## Cancellation And Recovery
 
 A CLI invocation performs one synchronous request and creates no durable run