docs: add compaction best practices guide

[ajjucoder]

Summary

This PR adds a new documentation file (COMPACTION.md) that provides best practices for preserving context during Claude Code's auto-compaction feature.

Problem

When Claude Code reaches ~95% token capacity, it auto-compacts the conversation history. Without proper guidance, this can cause loss of:

• Current task state and progress
• File modifications made during the session
• Technical decisions and their rationale
• Error messages and their resolutions

Solution

This guide provides users with recommended instructions to add to their ~/.claude/CLAUDE.md configuration file, including:

• What context to preserve in full detail
• What can be safely summarized
• A structured template for post-compaction context
• Priority ordering when space is limited

Testing

I have personally used these instructions across multiple long-running Claude Code sessions and confirmed they significantly improve context retention after compaction.

Related

• Original implementation: https://github.com/ajjucoder/claude-compaction-fix