{"method":["Six small Node.js repositories: a pagination bug across two files, a CLI flag with exact error text, a refactor that must keep every quirk, an LRU cache to a written spec, a queue race and strict TypeScript types. Each has 1 to 4 visible tests; the hidden checks live outside the repository and run only after the session ends.","Controls before the first session (Node v25.2.1): every base repository fails its hidden checks and every reference patch passes all of them.","Claude Code 2.1.286 headless with the sonnet and opus models at the default effort; tools Bash, Read, Edit, Write, Glob, Grep; no web tools, MCP servers or sub-agents; the OS sandbox on, writes limited to the repository, no network; setting sources off. Codex CLI exec with GPT-6.1 Sol at medium effort, workspace-write sandbox, no network, user config ignored (its version was not recorded).","6 tasks × 2 repetitions × 3 agents = 36 sessions with a 10-minute timeout; nothing retried. The Claude Code and Codex CLI lanes ran at the same time on one machine with different accounts.","Pass = every hidden check passes; no partial credit. Recorded per session: wall time, tool calls, tokens as reported, files touched, lines changed against the base commit, commits and edits outside the repository.","Gemini CLI 0.16.0 was probed first: it asked for a browser login, so it was not run and is not counted. The protocol was declared after the controls and before the first session."]}