Every AI companion promises "memory." Most implement it as a vector database that retrieves relevant conversation snippets. It works for basic factual recall but completely fails at the thing that actually matters: making the AI feel like it knows you. Real persistent memory is an architectural challenge that spans database design, context management, and behavioral modeling. Here is how it works when done right. The three memory layers Effective AI companion memory operates on three distinct layers, each serving a different function. Layer 1: Session context (Redis or in-memory). This is the hot state -the current conversation buffer, recent messages, and active emotional context. It lives in memory for fast access and gets updated with every message. Think of it as the AI's short-term memory: what happened in the last few minutes. Layer 2: Structured memory (PostgreSQL or similar).…