[plan] Add engine comparison table to engines.md

[github-actions]

Context

As identified in discussion #12027, users lack a clear comparison between engines to make informed decisions. The current documentation explains each engine separately but never compares them directly.

Problem

• Claude Code users want to know "what am I giving up by not using Copilot?"
• No table showing feature parity across engines
• No guidance on "when to choose X vs Y"
• Users cannot easily assess which engine fits their needs

Objective

Add a comprehensive engine comparison table and "when to choose" guidance to help users select the appropriate engine.

Proposed Solution

Add to docs/src/content/docs/reference/engines.md after the introduction:

## Engine Comparison

| Feature | Copilot CLI | Claude | Codex |
|---------|-------------|--------|-------|
| All workflow triggers | ✅ | ✅ | ✅ |
| GitHub tools & MCP | ✅ | ✅ | ✅ |
| Safe outputs | ✅ | ✅ | ✅ |
| Custom MCP servers | ✅ | ✅ | ✅ |
| Web search (MCP) | ⚠️ Tavily MCP | ✅ Built-in + MCP | ⚠️ Tavily MCP |
| Agent sessions | ✅ | ❌ | ❌ |
| Bot assignments | ✅ | ❌ | ❌ |
| Setup complexity | PAT required | API key | API key |

### When to Choose

- **Claude**: Best for general-purpose automation, excellent reasoning, simple API key setup
- **Copilot**: Best when you need agent sessions or Copilot bot assignments
- **Codex**: Alternative OpenAI-based option for API-based workflows

> [!TIP]
> 95%+ of features work identically across all engines. Only Copilot-specific features (agent sessions, bot assignments) require Copilot.

Files to Modify

• docs/src/content/docs/reference/engines.md

Acceptance Criteria

• Add comparison table showing feature parity
• Add "When to Choose" section with clear guidance
• Add tip callout about 95%+ feature parity
• Verify table renders correctly in documentation site
• Ensure accuracy of feature comparison (based on current codebase)

References

• Discussion 🔍 Claude Code User Documentation Review - January 27, 2026 #12027 - Priority 1 recommendation (Major Obstacle 2)

AI generated by Plan Command for discussion #12027

[github-actions]

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