Agent Memory That Survives Session Resets: The Vault Pattern in Practice

The Problem: Every Session Starts Blind Claude Code sessions are stateless by default. When a session ends — timeout, crash, deliberate close — the context is gone. For a solo agent on a single task, that's fine. For a five-agent system running continuously, it's a crisis. We needed agents to remember: What they were working on when the session ended Decisions made in past sessions Facts about system state not derivable from the code Instructions that apply across all sessions What Doesn't Work Database-backed memory: Added a third dependency. Overkill for structured text. Harder to inspect. Full conversation history in system prompt: Context window fills up fast. Most content irrelevant to the current task. CLAUDE.md alone: Works for stable facts. Breaks down for dynamic state — queue depth, blockers, what just changed. The Vault Pattern A tiered file system: vault/ MEMORY.md # index — always loaded into context us