forward --append-system-prompt-file and --system-prompt-file to claude - #23
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umputun merged 1 commit intoJul 31, 2026
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Claude Code accepts the system prompt either inline (--append-system-prompt, --system-prompt) or from a file (--append-system-prompt-file, --system-prompt-file). fya's forward allowlist carries only the inline pair, so passing either file variant fails fast with "unknown flag" before claude starts. The file variants matter for large assembled system prompts: an inline prompt rides argv and hits the kernel's MAX_ARG_STRLEN (128 KiB per string), failing execve with E2BIG. Delivering it via a file removes that ceiling, but under fya the flag is rejected, so the PTY path is stuck on the inline form. Both are ordinary value flags, so they belong in forwardValue next to their inline counterparts.
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Claude Code accepts the system prompt either inline (
--append-system-prompt,--system-prompt) or from a file (--append-system-prompt-file,--system-prompt-file). The forward allowlist inapp/options/options.gocarries only the inline pair, so passing either file variant fails fast withunknown flag: --append-system-prompt-filebefore claude is ever started.Why the file variants matter
An inline system prompt rides argv, so it is bounded by the kernel's
MAX_ARG_STRLEN— 128 KiB per string, independent ofARG_MAX. Past that,execvefails withE2BIGand the process dies before claude runs. We hit this with a large assembled system prompt (agent rules composed from several layers).Claude's file variants remove that ceiling entirely, which is the natural fix — but under
fyathe flag is rejected, so the PTY path has no way to use it and stays on the inline form.Change
Both are ordinary value flags (
--flag <path>), so they go intoforwardValuenext to their inline counterparts.--system-prompt-fileis included for symmetry, since--system-promptis already forwarded.Extended
TestParseForwardedFlagswith both flags;go build ./...andgo test ./...are green.