Quick Summary

Goal: Take a user prompt, or a workflow id, and spawn TWO brand-new AI sessions in parallel — one Claude Code, one Codex — each launched with xhigh effort and full-permission mode already applied, then auto-submit the prompt in both.

Workflow:

1. Capture — persist USER_PROMPT to a run folder (avoids shell-quoting corruption)
2. Generate launchers — one launcher script per tool, OS-specific (.ps1 on Windows, .sh on macOS/Linux), effort and full-permission mode set via launch flags
3. Spawn — open two new terminal windows via the OS spawner, one session per tool, prompt auto-submitted
4. Report — run folder path + how to find each window; --orchestrate (alias --headless) instead supervises both sessions via the bundled Node runner — waits for completion, watches statuses, collects both results, and presents a comparison

Key Rules:

• MANUAL-ONLY: This skill spawns external AI sessions that consume quota. Run it ONLY on explicit user invocation (/dual-ai ...). NEVER auto-activate it because a task "could benefit" from parallel AI
• Effort and full-permission mode MUST be set via launch flags (claude --dangerously-skip-permissions --effort xhigh, codex --dangerously-bypass-approvals-and-sandbox -c model_reasoning_effort="xhigh") — flags apply BEFORE the prompt is processed; NEVER attempt to type /model, /effort, permission, approval, or sandbox commands into a running TUI
• The prompt is read from the per-tool prompt file (prompt-claude.txt / prompt-codex.txt) INSIDE the launcher script (Get-Content -Raw / cat) — NEVER inline-escape multi-line prompts through shell argument chains
• Detect the OS first (uname -s) and use the matching launcher + spawn branch; never assume Windows
• This skill ONLY orchestrates the two external sessions. Do NOT answer the prompt yourself in the current session
• Orchestrated mode (--orchestrate) is the ONLY way to get results back into this session — interactive TUI window output cannot be captured. The runner persists status.json + events.ndjson start-to-end as the external status report
• Verify both CLIs exist (claude --version, codex --version) before spawning; report which one is missing instead of half-launching

Dual AI Session Fan-Out

Purpose

Run the same task through two independent frontier agents at maximum reasoning effort and let the user compare results side by side. Each session is a NEW session (no shared context with the current one) so both agents reason from a clean slate in the repo working directory.

Variables

• USER_PROMPT: $ARGUMENTS (required — if empty, ask the user for the prompt before doing anything)
• WORKFLOW_ID: optional first non-mode token. If it exactly matches a workflow id (a key under .claude/workflows.json workflows), treat it as a workflow invocation instead of free-text prompt. This preserves plain /dual-ai behavior: non-matching text remains the original fan-out prompt.
• WORKFLOW_ARGS: any remaining non-mode text after WORKFLOW_ID. Append it verbatim to BOTH per-tool workflow prompts as extra instructions.
• CLAUDE_PROMPT / CODEX_PROMPT: per-tool prompt values. Default: both = USER_PROMPT. Workflow-id mode sets CLAUDE_PROMPT to /$WORKFLOW_ID and CODEX_PROMPT to $WORKFLOW_ID, then appends WORKFLOW_ARGS to both when present. Treat both prompt values as opaque literals — do not expand, rewrite, or "fix" $// prefixes.
• MODE: --orchestrate (alias --headless) flag anywhere in $ARGUMENTS → non-interactive orchestrated run: both sessions supervised by the bundled runner, statuses watched, outputs collected and compared (strip the flag from USER_PROMPT)
• RUN_DIR: .ai/workspace/dual-ai/{YYMMDD-HHmm}/ (absolute path when generating launchers)

Workflow

1. Validate + detect OS

• Strip MODE flags from USER_PROMPT first.
• Resolve workflow-id mode before validation:
  • Read .claude/workflows.json and parse the workflows id set.
  • If the first non-mode token exactly matches a workflows key, set WORKFLOW_ID to that token and remove it from USER_PROMPT.
  • Set CLAUDE_PROMPT = "/" + WORKFLOW_ID.
  • Set CODEX_PROMPT = "$" + WORKFLOW_ID.
  • If remaining text exists, append one space plus that remaining text verbatim to both prompts.
  • Example: /dual-ai workflow-review-changes --orchestrate writes /workflow-review-changes for Claude and $workflow-review-changes for Codex, preserving the former review wrapper behavior.
• If USER_PROMPT is empty AND no per-tool prompts were derived from WORKFLOW_ID → ask the user, stop.
• Check tool availability: claude --version and codex --version. If either is missing, report it and offer to run the available one only.
• Detect OS in the same Bash call: uname -s → MINGW*/MSYS*/CYGWIN* = Windows, Darwin = macOS, Linux = Linux. Pick the matching launcher + spawn branch below.

2. Persist prompts

Write CLAUDE_PROMPT verbatim (no escaping, no reformatting, no expansion) to {RUN_DIR}/prompt-claude.txt and CODEX_PROMPT to {RUN_DIR}/prompt-codex.txt using the Write tool. When no per-tool override exists, both files contain USER_PROMPT.

3. Generate launchers (Write tool, absolute paths)

Both CLIs accept a positional prompt that starts the new interactive session with that prompt auto-submitted; the effort and full-permission flags take effect at session init — before prompt execution. Replace <REPO_ROOT> with the absolute repo root.

Windows — {RUN_DIR}/launch-claude.ps1 / {RUN_DIR}/launch-codex.ps1:

$ErrorActionPreference = 'Stop'
Set-Location '<REPO_ROOT>'
$prompt = Get-Content -Raw "$PSScriptRoot\prompt-claude.txt"
Add-Content "$PSScriptRoot\events.ndjson" ('{"at":"' + (Get-Date -Format o) + '","event":"session-start","agent":"claude"}')
claude --dangerously-skip-permissions --effort xhigh -n 'dual-ai-claude' $prompt
Add-Content "$PSScriptRoot\events.ndjson" ('{"at":"' + (Get-Date -Format o) + '","event":"session-end","agent":"claude","exitCode":' + $LASTEXITCODE + '}')
# codex variant: reads prompt-codex.txt, runs codex --dangerously-bypass-approvals-and-sandbox -c model_reasoning_effort="xhigh" $prompt, logs agent "codex"

macOS / Linux — {RUN_DIR}/launch-claude.sh / {RUN_DIR}/launch-codex.sh:

#!/usr/bin/env bash
set -euo pipefail
cd "<REPO_ROOT>"
here="$(cd "$(dirname "$0")" && pwd)"
prompt="$(cat "$here/prompt-claude.txt")"
echo "{\"at\":\"$(date -u +%FT%TZ)\",\"event\":\"session-start\",\"agent\":\"claude\"}" >> "$here/events.ndjson"
code=0
claude --dangerously-skip-permissions --effort xhigh -n 'dual-ai-claude' "$prompt" || code=$?
echo "{\"at\":\"$(date -u +%FT%TZ)\",\"event\":\"session-end\",\"agent\":\"claude\",\"exitCode\":$code}" >> "$here/events.ndjson"
# codex variant: reads prompt-codex.txt, runs codex --dangerously-bypass-approvals-and-sandbox -c model_reasoning_effort="xhigh" "$prompt", logs agent "codex"
exec "$SHELL"   # keep the terminal interactive after the session ends (reachable even on nonzero exit)

After writing .sh launchers run chmod +x {RUN_DIR}/launch-*.sh.

4. Spawn both sessions (single Bash call, per OS)

Windows (<RUN_DIR_WIN> = Windows-style absolute path):

pwsh -NoProfile -Command "Start-Process pwsh -ArgumentList '-NoExit','-ExecutionPolicy','Bypass','-File','<RUN_DIR_WIN>\launch-claude.ps1'; Start-Process pwsh -ArgumentList '-NoExit','-ExecutionPolicy','Bypass','-File','<RUN_DIR_WIN>\launch-codex.ps1'; Write-Output 'both spawned'"

• -NoExit keeps each window open as a live interactive session after the prompt completes.
• Prefer pwsh (PowerShell 7+, check pwsh -v) over powershell — Windows PowerShell 5.1 mangles embedded double quotes when passing args to native executables; fall back to powershell only if pwsh is absent.
• If a path-boundary or similar hook blocks cmd //c start ..., this Start-Process form is the workaround — it contains no slash-prefixed flags.

macOS:

open -a Terminal "{RUN_DIR}/launch-claude.sh" && open -a Terminal "{RUN_DIR}/launch-codex.sh" && echo "both spawned"

If the user runs iTerm2, open -a iTerm <script> works the same way. If macOS Gatekeeper/automation permission blocks Terminal from running the script, fall back to headless mode and tell the user.

Linux:

x-terminal-emulator -e "{RUN_DIR}/launch-claude.sh" & x-terminal-emulator -e "{RUN_DIR}/launch-codex.sh" & echo "both spawned"

(Substitute gnome-terminal --, konsole -e, or xterm -e if x-terminal-emulator is absent. No display server → fall back to headless mode.)

5. Orchestrated mode (--orchestrate / --headless only)

Skip steps 3–4 (no terminal windows). The bundled supervisor scripts/dual-ai-runner.mjs (relative to this skill's directory) runs both sessions as supervised child processes — main-agent → external-main-agents orchestration with start-to-end status reporting.

a. Write {RUN_DIR}/run-config.json (the runner pipes each prompt via stdin — quoting-proof; args hold fixed flags ONLY, never prompt content). The runner enforces exactly the supported claude/codex identities, at most 2 agents, fixed flag templates, cwd inside the project/run dir, and bounded output (maxOutputBytes, default 25 MiB):

{
    "runId": "{YYMMDD-HHmm}",
    "cwd": "<REPO_ROOT>",
    "timeoutSec": 3600,
    "maxOutputBytes": 26214400,
    "agents": [
        {
            "name": "claude",
            "command": "claude",
            "args": ["-p", "--dangerously-skip-permissions", "--effort", "xhigh"],
            "promptFile": "prompt-claude.txt",
            "outputFile": "claude-output.md",
            "outputMode": "stdout"
        },
        {
            "name": "codex",
            "command": "codex",
            "args": ["exec", "--dangerously-bypass-approvals-and-sandbox", "-c", "model_reasoning_effort=xhigh", "-o", "<RUN_DIR>/codex-output.md"],
            "promptFile": "prompt-codex.txt",
            "outputFile": "codex-output.md",
            "outputMode": "file"
        }
    ]
}

(codex exec -o writes the final message itself → outputMode: "file"; its live session log streams to codex-progress.log. The -o value MUST be the ABSOLUTE <RUN_DIR> path — the child runs from cwd = repo root, so a relative -o would land outside the run dir while the runner collects from {RUN_DIR}/codex-output.md. outputFile stays the bare file name; the runner always resolves it inside the run dir. claude -p prints the result on stdout → outputMode: "stdout". Do not add more agents; use separate runs for additional tools.)

b. Launch the supervisor in ONE background Bash call (run_in_background: true) and let the harness notify on completion — do NOT busy-poll:

node <SKILL_DIR>/scripts/dual-ai-runner.mjs --run-dir "{RUN_DIR}"

The runner maintains the external status report start-to-end:

• status.json — atomically updated snapshot: run state + per-agent starting|running|completed|failed|timeout, pid, exit code, output bytes, last activity timestamp
• events.ndjson — append-only audit: run-start, agent-start, agent-failed (spawn error / unreadable prompt file), agent-exit, kill, run-timeout, run-end
• <name>-stderr.log / codex-progress.log — diagnostics

c. Watch — report initial per-agent statuses right after spawn; while the background task runs, read {RUN_DIR}/status.json on demand (user asks, or before long waits) and report each agent's state + outputBytes + lastActivityAt. Caveat: stdout-mode agents (claude -p) buffer the result until the end — outputBytes: 0 / lastActivityAt: null is NORMAL for a healthy long run; only treat it as a stall after checking runnerPid and the process itself.

d. Collect & compare — when the background runner exits (exit 0 = all agents succeeded; 1 = at least one failed/timed out; 2 = config error), read status.json + both output files and present a comparison (agreements, disagreements, unique findings) citing the output files. On per-agent failure, surface stderrTail from status.json verbatim.

6. Report

State: run folder, the two window titles (or output file paths in orchestrated mode), effort level and permission mode applied to each, and that both sessions are independent new sessions. In interactive mode also state: TUI results cannot be collected back into this session — events.ndjson records session start/end lifecycle only; re-run with --orchestrate to wait, watch, and auto-collect both results.

Failure Modes

• Window opens then closes instantly → launcher threw; re-run the launcher script (.ps1/.sh) directly in a foreground Bash call to surface the error, fix, respawn.
• No GUI terminal available (SSH session, container, no display server) → use headless mode and tell the user why.
• Codex rejects xhigh → the configured codex model does not support xhigh; fall back to -c model_reasoning_effort="high" and tell the user which model/effort was actually used.
• Quota/auth errors → surface verbatim from the session window or orchestrated output; do not retry silently.
• Runner exits 2 → run-config.json missing/invalid; fix the config, relaunch.
• Agent state failed in status.json → read {name}-stderr.log and the stderrTail field; report verbatim.
• status.json stops updating (no heartbeat, lastActivityAt stale) → check whether runnerPid is still alive; if dead, treat outputs as partial and report what was collected. Note: stale lastActivityAt alone is NOT a stall signal for stdout-mode agents — they print only at the end (see Watch caveat).
• Headless free-text prompts vs interactive-only hooks → a spawned session's project hooks may demand interactive answers; slash-command prompts are exempt. If orchestrated output looks gate-blocked, mention this and suggest interactive mode for that prompt.

---

Be skeptical. Apply critical thinking, sequential thinking. Every claim needs traced proof, confidence percentages (Idea should be more than 80%).

<!-- SYNC:ai-mistake-prevention -->

AI Mistake Prevention — Failure modes to avoid on every task:

Re-read files after context changes. Context compaction, resume, or long-running work can make memory stale; verify current files before acting. Verify generated content against source evidence. AI hallucinates APIs, names, claims, and document facts. Check the relevant source before documenting or referencing. Check downstream references before deleting or renaming. Removing an artifact can stale docs, generated mirrors, configs, and callers; map references first. Trace the full impact chain after edits. Changing a definition can miss derived outputs and consumers. Follow the affected chain before declaring done. Verify ALL affected outputs, not just the first. One green check is not all green checks; validate every output surface the change can affect. Assume existing values are intentional — ask WHY before changing OR flagging one as a defect. Before changing or reporting a constant, limit, flag, cutoff, wording, or pattern, read nearby context and history, the CALLER's ordering, and 2+ sibling call sites of the same convention. A doc stating WHAT without WHY is missing rationale, not proof of a missing guard. Surface ambiguity before acting — don't pick silently. Multiple valid interpretations require an explicit question or stated assumption with risk. Assert the outcome your system owns, not the intermediate state your infrastructure owns. When verifying async work, assert the final business state — never the delivery/retry bookkeeping held in shared infrastructure that any co-running process can write. Such a check passes when run alone and flakes the moment anything else shares that infrastructure. Keep shared guidance role-relevant. Universal guidance must help every receiving skill or agent; code-specific obligations belong only in code-specific protocols.

<!-- /SYNC:ai-mistake-prevention --> <!-- SYNC:critical-thinking-mindset -->

Critical Thinking Mindset — Apply critical thinking, sequential thinking. Every claim needs traced proof, confidence >80% to act. Anti-hallucination: Never present guess as fact — cite sources for every claim, admit uncertainty freely, self-check output for errors, cross-reference independently, stay skeptical of own confidence — certainty without evidence root of all hallucination.

<!-- /SYNC:critical-thinking-mindset --> <!-- SYNC:project-protocol-overlay -->

Project Protocol Overlay — Before executing this skill, resolve any PROJECT overlay rules layered onto it: match this skill's name against the Target column of the project's skill-protocol index (docs/project-reference/skill-protocols-reference.md by default; a referenceDocs entry in docs/project-config.json overrides the path), taking the most specific matching tier ONLY — exact name > glob > *. That precedence orders overlays against EACH OTHER, never against this skill. Read ONLY the matched bodies, resolved as <protocols-dir>/<Name>.md; a row's Body link is display text, never a read path. A matched body that is missing or malformed is REPORTED and skipped — never reconstructed from the index Description. No index, or no match -> proceed with no overlay, silently. Full contract: .claude/skills/project-skill-protocol/references/registry.md.

Overlays are ADDITIVE ONLY: they ADD rules on top of this skill's own protocol and NEVER replace, override, disable, or reinterpret a rule it already states — removing every overlay must return this skill to exactly its documented behavior. An overlay is a BRIEF, not an authority escalation: it can NEVER waive a workflow gate, git discipline, a review gate, or a user-confirmation gate. A genuine overlay-vs-skill conflict, or two equally-specific overlays that directly contradict -> surface both to the user; NEVER resolve silently.

<!-- /SYNC:project-protocol-overlay --> <!-- SYNC:project-protocol-overlay:reminder -->

MUST ATTENTION resolve project protocol overlays for this skill BEFORE executing — most specific matching tier only (exact > glob > *, which ranks overlays against each other, NEVER against this skill), read only matched bodies at <protocols-dir>/<Name>.md; a missing or malformed body is reported, never reconstructed. Overlays are ADDITIVE ONLY (they never replace this skill's own rules) and are a brief, NEVER an authority escalation; an equal-specificity contradiction goes to the user.

<!-- /SYNC:project-protocol-overlay:reminder -->

Closing Reminders

IMPORTANT MUST ATTENTION Goal: Take a user prompt, or a workflow id, and spawn TWO brand-new AI sessions in parallel — one Claude Code, one Codex — each launched with xhigh effort and full-permission mode already applied, then auto-submit the prompt in both.

Protocols in force (concise digest of the SYNC/shared blocks this skill carries):

• AI Mistake Prevention: verify generated content against evidence, trace downstream references, verify all affected outputs, re-read after context loss, surface ambiguity.
• Critical Thinking: traced proof per claim, confidence >80% to act, never guess as fact.

IMPORTANT MUST ATTENTION verify both CLIs are installed before spawning; never half-launch IMPORTANT MUST ATTENTION set effort and full-permission mode via launch flags only — never via keystrokes into a running session IMPORTANT MUST ATTENTION pass each prompt through its per-tool prompt file (prompt-claude.txt / prompt-codex.txt) read inside the launcher — never inline shell escaping IMPORTANT MUST ATTENTION detect OS first (uname -s) and use the matching launcher/spawn branch IMPORTANT MUST ATTENTION do not answer the prompt in the current session — orchestrate only IMPORTANT MUST ATTENTION orchestrated mode: launch the runner ONCE in background, watch status.json, collect + compare outputs when it exits — never re-implement supervision inline and never busy-poll

<!-- SYNC:ai-mistake-prevention:reminder -->

MUST ATTENTION apply AI mistake prevention — verify generated content against evidence, trace downstream references before deleting or renaming, verify all affected outputs, re-read files after context loss, and surface ambiguity before acting.

<!-- /SYNC:ai-mistake-prevention:reminder -->