# Architecture Overview

```mermaid
sequenceDiagram
    participant User
    participant Frontend as React SPA
    participant Backend as NestJS API
    participant Cache as In-Memory Cache
    participant MOEX as MOEX ISS

    User->>Frontend: Search / View instrument
    Frontend->>Backend: GET /api/v1/securities/search?q=SBER
    Backend->>Cache: getOrFetch('search:sber')
    alt Cache miss
        Cache->>Backend: null
        Backend->>MOEX: GET /iss/securities?q=SBER
        MOEX-->>Backend: raw data
        Backend->>Cache: set('search:sber', normalized, TTL=3600)
    else Cache hit
        Cache-->>Backend: cached data
    end
    Backend-->>Frontend: normalized response
    Frontend-->>User: rendered UI
```