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fix: clear error when system_prompt hits OS argv length limit #1098

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fix: clear error when system_prompt hits OS argv length limit #1098

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24 changes: 23 additions & 1 deletion src/claude_agent_sdk/_internal/transport/subprocess_cli.py
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Original file line number Diff line number Diff line change
Expand Up @@ -288,7 +288,29 @@ def _build_command(self) -> list[str]:
if self._options.system_prompt is None:
cmd.extend(["--system-prompt", ""])
elif isinstance(self._options.system_prompt, str):
cmd.extend(["--system-prompt", self._options.system_prompt])
# Linux/macOS enforce MAX_ARG_STRLEN (32 * PAGE_SIZE) per argv element.
# A huge --system-prompt string fails at execve with "Argument list too long"
# before any API request. Prefer the file form above that threshold.
prompt = self._options.system_prompt
max_arg_strlen = None
if hasattr(os, "sysconf"):
try:
page = os.sysconf("SC_PAGE_SIZE")
if isinstance(page, int) and page > 0:
max_arg_strlen = 32 * page
except (ValueError, OSError, AttributeError):
max_arg_strlen = None
if max_arg_strlen is not None:
size = len(prompt.encode("utf-8"))
if size >= max_arg_strlen:
raise CLIConnectionError(
f"system_prompt is {size} bytes, which meets/exceeds the OS "
f"per-argument limit of {max_arg_strlen} bytes (MAX_ARG_STRLEN). "
"Pass a file instead, e.g. "
'system_prompt={"type": "file", "path": "/path/to/prompt.txt"} '
"(maps to --system-prompt-file)."
)
cmd.extend(["--system-prompt", prompt])
else:
sp = self._options.system_prompt
if sp.get("type") == "file":
Expand Down