english/.opencode/skills/context-engineering/references/memory-systems.md

Memory Systems

Architectures for persistent context beyond the window.

Memory Layer Architecture

Layer	Scope	Persistence	Use Case
L1: Working	Current window	None	Active reasoning
L2: Short-Term	Session	Session	Task continuity
L3: Long-Term	Cross-session	Persistent	User preferences
L4: Entity	Per-entity	Persistent	Consistency
L5: Temporal Graph	Time-aware	Persistent	Evolving facts

Benchmark Performance (DMR Accuracy)

System	Accuracy	Approach
Zep	94.8%	Temporal knowledge graphs
MemGPT	93.4%	Hierarchical memory
GraphRAG	75-85%	Knowledge graphs
Vector RAG	60-70%	Embedding similarity

Vector Store with Metadata

class MetadataVectorStore:
    def add(self, text, embedding, metadata):
        doc = {
            "text": text, "embedding": embedding,
            "entities": metadata.get("entities", []),
            "timestamp": metadata.get("timestamp")
        }
        self.index_by_entity(doc)

    def search_by_entity(self, entity, k=5):
        return self.entity_index.get(entity, [])[:k]

Temporal Knowledge Graph

class TemporalKnowledgeGraph:
    def add_fact(self, subject, predicate, obj, valid_from, valid_to=None):
        self.facts.append({
            "triple": (subject, predicate, obj),
            "valid_from": valid_from,
            "valid_to": valid_to or "current"
        })

    def query_at_time(self, subject, predicate, timestamp):
        for fact in self.facts:
            if (fact["triple"][0] == subject and
                fact["valid_from"] <= timestamp <= fact["valid_to"]):
                return fact["triple"][2]

Memory Retrieval Patterns

Pattern	Query	Use Case
Semantic	"Similar to X"	General recall
Entity-based	"About user John"	Consistency
Temporal	"Valid on date"	Evolving facts
Hybrid	Combine above	Production

File-System-as-Memory

memory/
├── sessions/{id}/summary.md
├── entities/{id}.json
└── facts/{timestamp}_{id}.json

Guidelines

1. Start with file-system-as-memory (simplest)
2. Add vector search for scale
3. Use entity indexing for consistency
4. Add temporal awareness for evolving facts
5. Implement consolidation for health
6. Measure retrieval accuracy

Related

• Context Fundamentals
• Multi-Agent Patterns