Add example workflow for PR review with session caching

[ranyhb]

Overview

Adds a new workflow example (pr-review-with-caching.yml) that demonstrates how to use session caching with commit tracking to enable incremental PR reviews.

Key Features

• Session Caching: Caches Claude's session (~/.claude/projects) per PR and commit using GitHub Actions cache
• Commit Tracking: Tracks last reviewed commit SHA in .last-reviewed-commit file
• Dual Prompt System: Two environment variables for smart prompt selection:
  • PROMPT_FULL: Comprehensive prompt for first review
  • PROMPT_SIMPLE: Incremental prompt for subsequent reviews
• Session Continuity: Uses --continue flag when previous session exists
• Git Operations: Supports git diff, git log, and git cat-file for analyzing changes

How It Works

First Commit (Full Review):

1. No cached session exists
2. Loads PROMPT_FULL with comprehensive review instructions
3. Claude performs full PR review
4. Saves commit SHA to .last-reviewed-commit
5. Session cached with unique key

Subsequent Commits (Incremental Review):

1. Cache restored from previous commit via prefix match
2. Reads .last-reviewed-commit to get previous commit SHA
3. Loads PROMPT_SIMPLE with {LAST_COMMIT} variable injected
4. Claude uses --continue flag to resume from previous session
5. Reviews ONLY changes since last commit using git diff/log
6. Saves new commit SHA and updates cache

Benefits

• ⚡ Faster reviews - No re-analysis of entire PR every commit
• 🧠 Context preservation - Remembers previous discussions and decisions
• 🎯 Focused feedback - Only reviews new changes
• 💾 Per-PR isolation - Each PR has its own cache namespace

Testing

This workflow can be tested by:

1. Creating a test PR with multiple commits
2. Observing the full review on first commit
3. Pushing additional commits and seeing incremental reviews
4. Checking GitHub Actions cache for session persistence

[ranyhb]

@claude what do u think ?

[ranyhb]

@ashwin-ant what do u think? already tested and working