the backslash went missing somewhere between the model and the shell

Someone read 47,828 shell commands out of real agent sessions this week and found that the harness, not the model, had quietly rewritten about one call in eight among those carrying code or escape characters, and that all ten harnesses they tested altered at least one. The grim part is what happens next: four fifths of the commands with mangled backslashes ran to completion and reported no error whatsoever, so the agent saw a clean exit and carried on. When the failures were later diagnosed from the trajectory, the model was blamed for 95% of them, while more than half actually came from the hops between the model and the process. You pay for that twice, in retries and in misplaced trust, and the measured bill was 2.4 times the tokens per task that eventually worked. Which leaves the question none of our tooling answers: where is the assertion that the call the model wrote is byte-for-byte the call the operating system received?