Shut down on server-initiated HARD_RESET

Session is stale and not recoverable (lame duck).

TunnelKit/Sources/AppExtension/TunnelKitProvider.swift

@@ -652,7 +652,7 @@ extension TunnelKitProvider {
             }
         } else if let se = error as? SessionError {
             switch se {
-            case .negotiationTimeout, .pingTimeout:
+            case .negotiationTimeout, .pingTimeout, .staleSession:
                 return .timeout
                 
             case .badCredentials:

TunnelKit/Sources/Core/SessionError.swift

@@ -67,6 +67,9 @@ public enum SessionError: String, Error {
     
     /// The server couldn't ping back before timeout.
     case pingTimeout
+    
+    /// The session reached a stale state and can't be recovered.
+    case staleSession
 }
 
 extension Error {

TunnelKit/Sources/Core/SessionProxy.swift

@@ -326,12 +326,6 @@ public class SessionProxy {
     private func start() {
         loopLink()
         hardReset()
-
-        guard !keys.isEmpty else {
-            fatalError("Main loop must follow hard reset, keys are empty!")
-        }
-
-        loopNegotiation()
     }
     
     private func loopNegotiation() {
@@ -466,7 +460,10 @@ public class SessionProxy {
 //                deferStop(.shutdown, e)
 //                return
             }
-            if (code == .softResetV1) && (negotiationKey.state != .softReset) {
+            if (code == .hardResetServerV2) && (negotiationKey.state != .hardReset) {
+                deferStop(.shutdown, SessionError.staleSession)
+                return
+            } else if (code == .softResetV1) && (negotiationKey.state != .softReset) {
                 softReset(isServerInitiated: true)
             }
 
@@ -560,6 +557,10 @@ public class SessionProxy {
 
         let payload = hardResetPayload() ?? Data()
         negotiationKey.state = .hardReset
+        guard !keys.isEmpty else {
+            fatalError("Main loop must follow hard reset, keys are empty!")
+        }
+        loopNegotiation()
         enqueueControlPackets(code: .hardResetClientV2, key: UInt8(negotiationKeyIdx), payload: payload)
     }