sequenceDiagram
    participant F as Flutter App
    participant N as Next.js Server
    participant FS as Firestore
    participant U as User Browser
    participant P as Public Page

    F->>N: POST /api/shorten {shareId, type, originalUrl} (+x-api-key)
    N->>FS: Check short_links_index[type_shareId]
    alt not exists
        N->>FS: Create short_links{code} + index
    end
    N-->>F: { shortUrl, shortCode }

    F-->>U: Display shortUrl

    U->>N: GET /r/{code}
    N->>FS: Lookup short_links/{code}
    N->>FS: Increment clickCount (async)
    N-->>U: 302 Redirect → /s/{shareId} or /voice/{shareId}

    U->>P: Visit redirected page
    P->>N: GET /api/shared-notes/{shareId} | /api/voice-notes/{shareId}
    N->>FS: Fetch shared doc
    N-->>P: 200 JSON (content)
    P-->>U: Render read-only view