Google Agentic Architect - Subconcept 3.1: Four-Tier Memory Architecture

Deconstruct the physical storage backends and latency profiles of the four-tier agent memory hierarchy. Explain the operational characteristics of: 1) Short-Term Working State (Python in-memory heap or Memorystore/Redis, sub-5ms), 2) Durable Session State (Cloud Firestore or VertexAiSessionService, 10-50ms) for multi-turn history, 3) Episodic Long-Term Memory (AlloyDB pgvector or Vertex AI Vector Search, 20-80ms) for historical summaries and preferences, and 4) Semantic Entity Memory (Neo4j or Spanner Graph, 15-60ms) for structured domain facts. Discuss how agents dynamically read from and write to these tiers during a single reasoning turn.