sequenceDiagram
    participant U as User/Frontend
    participant API as API Worker
    participant D1 as D1 Database
    participant R2 as R2 Storage
    participant Q as Variant Queue
    participant AI as Workers AI

    U->>API: 1. POST /v1/images<br/>(metadata + filename)
    API->>D1: 2. Create image record<br/>(uploaded=0)
    D1-->>API: Image ID
    API->>API: 3. Generate signed<br/>upload token (JWT)
    API-->>U: 4. {imageId, uploadUrl, token}

    U->>API: 5. PUT /v1/upload/:id?token=xxx<br/>(binary image data)
    API->>API: 6. Validate token<br/>Strip EXIF (if enabled)
    API->>R2: 7. Store at<br/>{owner}/{album}/{filename}
    API->>D1: 8. Update uploaded=1
    API->>Q: 9. Enqueue variant generation
    API-->>U: 10. 201 Created

    Note over Q: Async Processing
    Q->>R2: 11. Fetch original image
    Q->>Q: 12. Generate variants:<br/>w128, w256, w512, w1024,<br/>w1536, w2048, thumb, og-image
    Q->>R2: 13. Store variants at<br/>{owner}/{album}/{filename}/{variant}
    Q->>D1: 14. Update variants_ready[]
    Q->>AI: 15. Classify image<br/>(labels, NSFW, colors, caption)
    AI-->>Q: Classification results
    Q->>D1: 16. Save AI metadata