sequenceDiagram
participant C as Client / AI Agent
participant S as Resource Server
participant F as Facilitator
participant B as Blockchain
C->>S: 1. HTTP Request
S-->>C: 2. 402 + PAYMENT-REQUIRED
C->>C: 3. Sign payment payload
C->>S: 4. Retry + PAYMENT-SIGNATURE
S->>F: 5. /verify
F-->>S: Valid
S->>F: 6. /settle
F->>B: Submit tx
B-->>F: Confirmed
F-->>S: Settlement proof
S-->>C: 7. 200 OK + Resource + PAYMENT-RESPONSE