Pass the prompt to the Claude Code CLI via stdin

[krllx]

The claude_code backend passes the whole prompt to claude -p as one argv string. Linux caps a single argument at 128 KiB (MAX_ARG_STRLEN), so once the prompt carries a few parent programs and artifacts, every call fails with [Errno 7] Argument list too long: 'claude' and the iteration is lost. I ran into it evolving a ~43 KB program: the first iterations worked, then all calls failed.

claude -p reads the prompt from stdin when no positional prompt is given, so the prompt now goes there. The system prompt still goes through --system-prompt.

Tests: the two tests that looked for the prompt in argv now check stdin, plus a new one with a 200 KB prompt. python -m unittest tests.test_claude_code_llm passes.

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}