I mean, if you take out the guard rails, here's codex in 46 lines of bash:

    #!/usr/bin/env bash
    set -euo pipefail
    
    # Fail fast if OPENAI_API_KEY is unset or empty
    : "${OPENAI_API_KEY:?set OPENAI_API_KEY}"
    MODEL="${MODEL:-gpt-5.2-chat-latest}"
    
    extract_text_joined() {
      # Collect all text fields from the Responses API output and join them
      jq -r '[.output[]?.content[]? | select(has("text")) | .text] | join("")'
    }
    
    apply_writes() {
      local plan="$1"
      echo "$plan" | jq -c '.files[]' | while read -r f; do
        local path content
        path="$(echo "$f" | jq -r '.path')"
        content="$(echo "$f" | jq -r '.content')"
        mkdir -p "$(dirname "$path")"
        printf "%s" "$content" > "$path"
        echo "wrote $path"
      done
    }
    while true; do
      printf "> "
      read -r USER_INPUT || exit 0
      [[ -z "$USER_INPUT" ]] && continue
      # File list relative to cwd
      TREE="$(find . -type f -maxdepth 6 -print | sed 's|^\./||')"
      USER_JSON="$(jq -n --arg task "$USER_INPUT" --arg tree "$TREE" \
        '{task:$task, workspace_tree:$tree,
          rules:[
            "Return ONLY JSON matching the schema.",
            "Write files wholesale: full final content for each file.",
            "If no file changes are needed, return files:[]"
          ] }')"
      RESP="$(
        curl -s https://api.openai.com/v1/responses \
          -H "Authorization: Bearer $OPENAI_API_KEY" \
          -H "Content-Type: application/json" \
          -d "$(jq -n --arg model "$MODEL" --argjson user "$USER_JSON" '{model:$model,input:[{role:"system",content:"You output only JSON file-write plans."},{role:"user",content:$user}],text:{format:{type:"json_schema",name:"file_writes",schema:{type:"object",additionalProperties:false,properties:{files:{type:"array",items:{type:"object",additionalProperties:false,properties:{path:{type:"string"},content:{type:"string"}},required:["path","content"]}}},required:["files"]}}}')"
      )"
      PLAN="$(printf "%s" "$RESP" | extract_text_joined)"
      apply_writes "$PLAN"
    done