fix(v1): transport unbounded harness input safely

[snimu]

Summary

• add binary stdin support to Runtime.run_program, using native pipes for subprocess and Docker and a runtime-file fallback for remote runtimes
• reject oversized or NUL-containing argv/environment entries before exec with an actionable error
• move unbounded task/system/message payloads off argv for Bash, Null, Claude Code, Codex, Pi, Terminus 2, and the Compact example
• move model-generated Bash and Terminus shell scripts from sh -c <script> to shell stdin
• keep existing program flags as compatibility inputs for Verifiers-owned harness programs

Motivation

Linux commonly limits each individual exec argument to about 128 KiB, independently of aggregate ARG_MAX. Large task prompts can therefore fail before a harness starts with OSError: [Errno 7] Argument list too long. The same unsafe argv pattern can fail under subprocess, Docker, Modal, or Prime because every backend eventually starts a process.

The general transport policy is:

1. stdin where the target CLI supports it;
2. runtime files where stdin is unavailable or a separate payload is required;
3. argv/environment only for bounded control values, guarded before launch.

Harnesses whose pinned external CLIs do not have verified stdin/file support (Kimi Code, mini-swe-agent, RLM) retain their current launch semantics but now fail early with a clear size error rather than an OS-level E2BIG.

Validation

• uv run ruff check .
• uv run ruff format --check .
• uv run pytest tests/v1/test_configs.py tests/v1/test_taskset.py -q
• existing Bash and Null subprocess E2E cases
• manual 200 KB binary/text stdin validation for SubprocessRuntime
• manual 200 KB Bash and Null payload validation with bounded launch argv
• ty diagnostics match the current-main baseline

The full local non-Prime/non-Modal matrix could not exercise Docker because Docker Desktop is unavailable on this machine; its Docker-selected failures were infrastructure errors. No tests were added.

[snimu]

Closing in favor of an environment-level design: large paragraph payloads will be written to the rollout workspace and consumed via Bash, so they no longer need to travel in the initial prompt.