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adding fallback to --system-prompt-file when --system-prompt is too long #427

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adding fallback to --system-prompt-file when --system-prompt is too long #427

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f660af1
adding fallback to --system-prompt-file when --system-prompt is too long
M-Alshoura Dec 17, 2025
7f3ddff
removed unnecessary check
M-Alshoura Dec 17, 2025
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21 changes: 21 additions & 0 deletions 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 @@ -335,6 +335,27 @@ def _build_command(self) -> list[str]:

# Check if command line is too long (Windows limitation)
cmd_str = " ".join(cmd)
if len(cmd_str) > _CMD_LENGTH_LIMIT and "--system-prompt" in cmd:
# Handle large --system-prompt by switching to --system-prompt-file
try:
sp_idx = cmd.index("--system-prompt")
sp_value = cmd[sp_idx + 1]
temp_file = tempfile.NamedTemporaryFile(
mode="w", suffix=".txt", delete=False, encoding="utf-8"
)
temp_file.write(sp_value)
temp_file.close()
self._temp_files.append(temp_file.name)
# Replace --system-prompt with --system-prompt-file
cmd[sp_idx] = "--system-prompt-file"
cmd[sp_idx + 1] = temp_file.name
logger.info(
f"System prompt length ({len(sp_value)}) exceeds limit. "
f"Using --system-prompt-file: {temp_file.name}"
)
except (ValueError, IndexError) as e:
logger.warning(f"Failed to optimize system prompt length: {e}")

if len(cmd_str) > _CMD_LENGTH_LIMIT and self._options.agents:
# Command is too long - use temp file for agents
# Find the --agents argument and replace its value with @filepath
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