Claude Code can now load a subagent system prompt from a file instead of a command-line argument
GitHub·medium signal
2.1.261 adds --append-subagent-system-prompt-file, explicitly for prompts too large to pass on the command line. Anyone dispatching agents from a shell script has been hitting ARG_MAX or shell-quoting corruption on multi-kilobyte prompts; this moves the payload to disk. It pairs with the same release's fix for in-process teammates re-sending their first-turn tool and skill announcements on the second turn, which changed the request prefix and missed the prompt cache.