{
  "schema_version": 1,
  "kind": "experience",
  "id": "claude-harness-to-codex-cli",
  "language": "en",
  "title": "Moving a Claude Code agent harness to Codex CLI: what had to change",
  "canonical_url": "https://aicqsohoo.com/experiences/claude-harness-to-codex-cli/",
  "json_url": "https://aicqsohoo.com/records/experience/claude-harness-to-codex-cli.en.json",
  "dates": {
    "observed_at": "2026-09-26 to 2026-09-27",
    "published_at": null,
    "modified_at": null
  },
  "content_sha256": "c73aa7d4368152084b4c23bf9b8e050d331d01103a38af5020643687eb357b91",
  "sources": [
    "https://github.com/simcoeforever/aicqsohoo/blob/main/data/experiences/claude-harness-to-codex-cli.json"
  ],
  "evidence": {
    "kind": "observed_run",
    "sample_size": "several dummy checks and 2 real runs",
    "confidence": {
      "level": "medium",
      "reason": "Each fix was checked with a dummy run and unit tests. Details apply to the Codex CLI version used at the time."
    },
    "verification_status": "human_summary_not_independently_verified"
  },
  "content": {
    "id": "claude-harness-to-codex-cli",
    "title": "Moving a Claude Code agent harness to Codex CLI: what had to change",
    "short_summary": "A small runner built around Claude Code was adapted to run the same experiment on Codex CLI. Three things mattered: stop the agent process while a human decides a request, give back file reading after disabling the shell, and remove built-in tools the other agent did not have.",
    "short_summary_ja": "Claude Code 向けに作った小さな実行の仕組みを Codex CLI に移した。大事だったのは、人の判断を待つ間はプロセスを止めること、シェルを切ったらファイルを読む道具を足すこと、相手に無い内蔵の道具を消すこと。",
    "problem": "Run the same agent experiment on two agent systems so the results can be compared, without the harness itself creating the difference.",
    "environment": "A Python runner that wakes the agent repeatedly, exposes MCP tools (wallet, request a human, record a decision), and logs everything to JSONL. Codex CLI in non-interactive mode, resuming the same session on each wake.",
    "agents": [
      "codex-cli-gpt6-astra"
    ],
    "model": "GPT-6 Astra (high effort)",
    "harness": "Codex CLI (codex exec / resume) driven by the same custom runner, shell disabled",
    "observed_at": "2026-09-26 to 2026-09-27",
    "attempts": [
      "First real run: the request tool returned immediately and Codex simply carried on, so the request sat undecided and the clock kept running. The run was kept only as a reference.",
      "Fix: when the agent makes a request, the runner stops the Codex process, waits for the human decision with the clock paused, and passes the decision in as the first message of the next wake.",
      "With the shell disabled Codex could not read its input files, so a small workspace-only tool (list, read, search) was added for Codex runs, rejecting paths outside the workspace.",
      "Disabled Codex's multi-agent, goal and ask-the-user tools so both systems had comparable tools. Some built-ins (a clock, a code mode that can call tools from JavaScript) could not be removed and were recorded as differences.",
      "Checked that the system prompt Codex received matched the original. It differed only by one trailing newline."
    ],
    "failures": [
      "A tool that returns 'pending' does not make an agent wait. It keeps working.",
      "Token counts are lost for a wake that is stopped mid-way."
    ],
    "outcome": "The second real run blocked correctly on its request (36 minutes of human waiting excluded from its time budget) and gave a comparable result.",
    "confidence": {
      "level": "medium",
      "reason": "Each fix was checked with a dummy run and unit tests. Details apply to the Codex CLI version used at the time."
    },
    "reusable_lessons": [
      "If a human must decide mid-run, enforce the wait in the harness. Do not rely on the model to wait.",
      "Turning off the shell also turns off file reading for some agents. Replace it with a narrow read-only tool.",
      "List the tools each agent system really exposes. Built-ins you cannot switch off are part of what you are comparing.",
      "Save the exact settings and input hashes for every run so it can be repeated later with newer agents."
    ],
    "tags": [
      "harness",
      "codex-cli",
      "claude-code",
      "human-in-the-loop",
      "mcp",
      "experiment-design"
    ],
    "related_experiences": [
      "stop-or-go-get-evidence"
    ],
    "evidence_kind": "observed_run",
    "sample_size": "several dummy checks and 2 real runs",
    "canonical_url": "https://aicqsohoo.com/experiences/claude-harness-to-codex-cli/"
  }
}