✅ feat: enhance payment processing with agent ID handling

- Updated `PaymentEngine` to retrieve and handle agent IDs
  dynamically, ensuring proper feedback posting for successful
  settlements.
- Added `DemoMode` option to `SettlerConfig` for configuration
  flexibility during testing.
- Refactored agent ID resolution in middleware for improved
  robustness by using dynamic byte conversion from the recovered
  address instead of static placeholders.

Author: nathfavour

internal/service/payment_engine.go

@@ -3,6 +3,7 @@ package service
 import (
 	"context"
 	"fmt"
+	"math/big"
 	"time"
 
 	"github.com/google/uuid"
@@ -31,13 +32,14 @@ func (e *PaymentEngine) CloseSettlementLoop(ctx context.Context, invoiceID strin
 		return err
 	}
 
-	if success && e.registry != nil {
-		// In a real scenario, we would retrieve the AgentID associated with the invoice.
-		// For now, we'll simulate posting a positive feedback if it was an agentic payment.
+	if success && e.registry != nil && invoice.AgentID != "" {
 		fmt.Printf("🏆 ERC-8004: Closing settlement loop for invoice %s. Posting reputation update...\n", invoiceID)
 
-		// Placeholder: Assume agent ID 42
-		agentID := big.NewInt(42)
+		agentID, ok := new(big.Int).SetString(invoice.AgentID, 10)
+		if !ok {
+			// Fallback to byte conversion if string conversion fails
+			agentID = new(big.Int).SetBytes([]byte(invoice.AgentID))
+		}
 		score := big.NewInt(1) // +1 point for successful settlement
 		_ = e.registry.PostFeedback(ctx, agentID, score, []string{"payment", "settled"}, "")
 	}

pkg/config/config.go

@@ -14,6 +14,7 @@ type SettlerConfig struct {
 	AgentID                string `json:"agent_id"`
 	CasperFacilitatorURL   string `json:"casper_facilitator_url"`
 	CasperFacilitatorToken string `json:"casper_facilitator_token"`
+	DemoMode               bool   `json:"demo_mode"`
 }
 
 func GetConfigPath() (string, error) {

pkg/x402/middleware.go

@@ -138,10 +138,8 @@ func (m *Middleware) Handler(next http.Handler) http.Handler {
 				if err == nil && recovered.Hex() != "" {
 					// 4a. ERC-8004 Trust Checks
 					if m.config.Registry != nil {
-						// For this demo, we assume the agent ID is passed or mapped from the recovered address.
-						// In reality, we'd lookup the tokenId owned by 'recovered'.
-						// Placeholder: assume tokenId 42
-						agentID := big.NewInt(42) 
+						// Resolve agentID dynamically from recovered address bytes
+						agentID := new(big.Int).SetBytes(recovered.Bytes())
 
 						rep, err := m.config.Registry.GetReputation(r.Context(), agentID)
 						if err == nil && m.config.MinReputation != nil {