Cmux Second Opinion

cmux-second-opinion — Second Opinion from Another AI

Get an independent code or spec review from a different AI agent in a separate cmux workspace.

Language Rules

1. Auto-detect input language → output in the same language
2. Japanese input → Japanese output, use references/second-opinion-guide.ja.md
3. English input → English output, use references/second-opinion-guide.md
4. Explicit override takes priority

Prerequisites

BEFORE requesting a second opinion, verify cmux environment:

echo $CMUX_SOCKET_PATH

• If empty or unset → stop with error:
  • EN: "Error: Not running inside a cmux session. Please start Claude Code from within cmux."
  • JA: "エラー: cmux セッション内で実行されていません。cmux 内で Claude Code を起動してください。"
• If set → proceed

Review Type Detection

Determine the review type from user input:

Review Criteria Mode

Determine how to use review_rules.md:

Detect review_rules.md:

find . -name "review_rules.md" -maxdepth 3 2>/dev/null

If not found → automatically fall back to "No criteria" mode.

Agent Selection

Select a reviewer that differs from the parent agent to ensure a different perspective.

User can override: "have Claude review this", "Gemini にレビューさせて", etc.

Verify reviewer is available:

which codex    # or whichever agent was selected

Code Review Flow

Step 1: Get Diff

# Staged + unstaged changes vs HEAD
git diff HEAD

# Or vs base branch (if on a feature branch)
git diff main...HEAD

If diff is empty → error: "No changes to review." / "レビュー対象の変更がありません。"

Step 2: Build Review Prompt

Construct the prompt in the same language as the user's input (auto-detected via Language Rules). The reviewer should receive instructions and produce output in that language.

Default mode (English):

Review the following code changes.
## Review Criteria
{content of review_rules.md}
In addition to the above criteria, share any issues you notice from your own perspective.
## Diff
{diff content}
## Output Format
### Critical (must fix)
### Improvements
### Good points

Default mode (日本語):

以下のコード変更をレビューしてください。
## レビュー基準
{review_rules.md の内容}
上記の基準に加えて、独自の視点で気づいた点があれば指摘してください。
## 変更差分
{diff の内容}
## 出力形式
### 重大（修正必須）
### 改善提案
### 良い点

No criteria mode (EN):

Review the following code changes from your own perspective.
Focus on code quality, security, performance, and best practices.
## Diff
{diff content}
## Output Format
### Critical (must fix) / ### Improvements / ### Good points

No criteria mode (JA):

以下のコード変更を自由な視点でレビューしてください。
コード品質、セキュリティ、パフォーマンス、ベストプラクティスの観点でお願いします。
## 変更差分
{diff の内容}
## 出力形式
### 重大（修正必須） / ### 改善提案 / ### 良い点

Criteria only mode: Same as default but without the "also share" / "独自の視点" instruction.

Step 3: Launch Reviewer, Send Prompt, Collect Results

1. Create surface: cmux new-split right → extract surface handle from output (OK surface:{N} workspace:{N})
   • Do NOT use cmux new-workspace — it may create a non-terminal surface that cannot receive commands. Use cmux new-split right (or down) instead.
2. Launch reviewer: cmux send --surface surface:{N} "{reviewer_command}\n"
3. Detect prompt: poll with cmux read-screen (3s intervals, 15s timeout)
4. Send review prompt: cmux send + cmux send-key return
5. Monitor completion: graduated polling (5s → 10s → 30s)
6. Collect results: cmux read-screen --surface surface:{N} --scrollback
7. Do NOT auto-close the reviewer pane. The user may want to review the output in the pane, scroll through history, or ask follow-up questions to the reviewer directly.

Spec Review Flow

Step 1: Locate Spec Files

ls .specs/{feature}/requirement.md .specs/{feature}/design.md .specs/{feature}/tasks.md 2>/dev/null

If no spec files found → error: "Spec files not found." / "仕様書が見つかりません。"

If {feature} is not specified, scan .specs/ and ask user to select.

Step 2: Build Review Prompt

Construct in the same language as user input (per Language Rules).

English:

Review the following specification documents.
{if default or criteria-only mode}
## Review Criteria
{content of review_rules.md} (apply relevant review perspectives only)
{end}
## Specifications
### requirement.md / ### design.md / ### tasks.md
{contents}
## Review Perspectives
- Missing or contradictory requirements?
- Design consistent with requirements?
- Task breakdown appropriate?
- Technically infeasible aspects?
- Security concerns?
## Output Format
### Critical Issues / ### Improvements / ### Good Points

日本語:

以下の仕様書をレビューしてください。
{if デフォルト or 基準のみモード}
## レビュー基準
{review_rules.md の内容}（該当する観点のみ適用）
{end}
## 仕様書
### requirement.md / ### design.md / ### tasks.md
{内容}
## レビュー観点
- 要件の漏れ・矛盾はないか
- 設計と要件の整合性はあるか
- タスク分解は適切か
- 技術的に実現困難な点はないか
- セキュリティ上の懸念はないか
## 出力形式
### 重大な問題 / ### 改善提案 / ### 良い点

Important: Do NOT pass inspection-report.md to the reviewer. The value of a second opinion is an independent perspective.

Step 3: Launch, Send, Collect

Same as Code Review Flow Step 3 (use cmux new-split right, not new-workspace).

Result Report

After collecting the reviewer's output, structure it in the same language as user input:

English:

## Second Opinion Result
**Reviewer**: {agent_name} | **Type**: {code / spec} | **Criteria Mode**: {mode}
### Summary
- Critical: {n} / Improvements: {n} / Good points: {n}
### Critical (Must Fix) / ### Improvements / ### Good Points

日本語:

## セカンドオピニオン結果
**レビュアー**: {agent_name} | **種別**: {code / spec} | **基準モード**: {mode}
### サマリー
- 重大: {n} 件 / 改善提案: {n} 件 / 良い点: {n} 件
### 重大（修正必須） / ### 改善提案 / ### 良い点

Report to the user in the parent session.

Error Handling

Notes

• This skill provides the mechanism for second opinions. Review quality depends on the reviewer agent's capabilities.
• For general task delegation (not review-specific), use cmux-delegate.
• For conversation forking, use cmux-fork.
• For detailed usage examples and troubleshooting, see the reference guide.