Implement zombie connection detection and cleanup in ConnectionManager; enhance tests for edge cases

ts/proxies/smart-proxy/connection-manager.ts

@@ -456,6 +456,48 @@ export class ConnectionManager extends LifecycleComponent {
       }
     }
     
+    // Also check ALL connections for zombie state (destroyed sockets but not cleaned up)
+    // This is critical for proxy chains where sockets can be destroyed without events
+    for (const [connectionId, record] of this.connectionRecords) {
+      if (!record.connectionClosed) {
+        const incomingDestroyed = record.incoming?.destroyed || false;
+        const outgoingDestroyed = record.outgoing?.destroyed || false;
+        
+        // Check for zombie connections: both sockets destroyed but connection not cleaned up
+        if (incomingDestroyed && outgoingDestroyed) {
+          logger.log('warn', `Zombie connection detected: ${connectionId} - both sockets destroyed but not cleaned up`, {
+            connectionId,
+            remoteIP: record.remoteIP,
+            age: plugins.prettyMs(now - record.incomingStartTime),
+            component: 'connection-manager'
+          });
+          
+          // Clean up immediately
+          this.cleanupConnection(record, 'zombie_cleanup');
+          continue;
+        }
+        
+        // Check for half-zombie: one socket destroyed
+        if (incomingDestroyed || outgoingDestroyed) {
+          const age = now - record.incomingStartTime;
+          // Give it 30 seconds grace period for normal cleanup
+          if (age > 30000) {
+            logger.log('warn', `Half-zombie connection detected: ${connectionId} - ${incomingDestroyed ? 'incoming' : 'outgoing'} destroyed`, {
+              connectionId,
+              remoteIP: record.remoteIP,
+              age: plugins.prettyMs(age),
+              incomingDestroyed,
+              outgoingDestroyed,
+              component: 'connection-manager'
+            });
+            
+            // Clean up
+            this.cleanupConnection(record, 'half_zombie_cleanup');
+          }
+        }
+      }
+    }
+    
     // Process only connections that need checking
     for (const connectionId of connectionsToCheck) {
       const record = this.connectionRecords.get(connectionId);