Technical Deep Dive

System Architecture

How the 8-agent LangGraph state machine, Neo4j Project Knowledge Graph (PKG), and Hybrid GraphRAG coordinate.

High-Level Infrastructure Architecture

┌─────────────────────────────────────────────────────────────────┐
│       Next.js 16 Web Dashboard    │  React Native Expo App      │
└──────────────────────────┬──────────────────────────────────────┘
                           │ HTTPS / JWT (Supabase JWKS)
                           ▼
┌─────────────────────────────────────────────────────────────────┐
│      FastAPI Gateway · AST Cypher Sanitizer · Rate Limiter      │
└────────────────┬─────────────────────────────┬──────────────────┘
                 │                             │
┌────────────────┴──────────┐    ┌─────────────┴────────────────┐
│  LangGraph Agent Ensemble  │    │    Persistence Layer         │
│  8 Agents · HITL Gate     │    │  Neo4j · ChromaDB · Redis    │
└───────────────────────────┘    └──────────────────────────────┘

AST Cypher Security Sandbox

Because STRAND allows natural language queries to generate dynamic Neo4j Cypher statements, standard regex filtering is insufficient. STRAND parses all LLM-generated Cypher into an Abstract Syntax Tree (AST).

Mutation Blocking

Blocks CREATE, MERGE, DELETE, SET on read routes.

Tenant Injection

Automatically injects tenant_id into MATCH clauses for isolation.

APOC / System Sandboxing

Blocks system procedures, file loads, and arbitrary code execution.

Hybrid GraphRAG (BM25 + Dense + Neo4j)

Brain Agent fuses lexical keyword matching (BM25) with semantic dense vector search (Chroma all-MiniLM-L6-v2) using Reciprocal Rank Fusion (RRF, k=60).

When retrieved chunks correspond to PKG entities with DERIVES_FROM lineage, STRAND traverses the 1-hop BIM graph neighborhood to answer questions about downstream equipment that pure vector RAG cannot find.