"Agent memory" is overloaded. Chat history, vector databases, local note files, static rules files, and shared project context are fundamentally different things being sold under one label. This talk separates them: private memory is one agent remembering user preferences; shared context is multiple agents and humans maintaining governed project state. Using a self-hosted MCP context registry as the case study, we show why the second category needs URIs instead of opaque embeddings, versions instead of append-only logs, grants instead of shared secrets, provenance instead of blind trust, and signals instead of polling. The audience will understand why "agent memory" products that focus on recall miss the harder problem of collaboration, governance, and portability across tools.