Update: I ended up building this into a full closed-loop pipeline. A PreToolUse hook detects context pressure at 65%, the agent writes a structured handover (task state, files, progress), tmux clears the session, and a rotator script injects the continuation into the fresh session.

The key insight from testing: rotating at 60-70% — before quality degrades — matters more than the rotation mechanism itself. At 80%+ auto-compact kicks in and races with any cleanup you try to do.

Wrote it up as a Show HN if anyone's curious: https://news.ycombinator.com/item?id=47152204