Add debug assertions

SignalServiceKit/src/Loki/Protocol/Multi Device/MultiDeviceProtocol.swift

@@ -90,6 +90,11 @@ public final class MultiDeviceProtocol : NSObject {
     /// See [Multi Device Message Sending](https://github.com/loki-project/session-protocol-docs/wiki/Multi-Device-Message-Sending) for more information.
     @objc(sendMessageToDestinationAndLinkedDevices:in:)
     public static func sendMessageToDestinationAndLinkedDevices(_ messageSend: OWSMessageSend, in transaction: YapDatabaseReadTransaction) {
+        if !messageSend.isUDSend && messageSend.recipient.recipientId() != getUserHexEncodedPublicKey() {
+            #if DEBUG
+            preconditionFailure()
+            #endif
+        }
         let message = messageSend.message
         let messageSender = SSKEnvironment.shared.messageSender
         if !isMultiDeviceRequired(for: message) {

SignalServiceKit/src/Messages/OWSMessageSender.m

@@ -487,6 +487,7 @@ NSString *const OWSMessageSenderRateLimitedException = @"RateLimitedException";
 {
     [self.udManager
         ensureSenderCertificateWithSuccess:^(SMKSenderCertificate *senderCertificate) {
+            OWSAssertDebug(senderCertificate != nil);
             dispatch_async([OWSDispatch sendingQueue], ^{
                 [self sendMessageToService:message senderCertificate:senderCertificate success:success failure:failure];
             });
@@ -927,6 +928,8 @@ NSString *const OWSMessageSenderRateLimitedException = @"RateLimitedException";
 {
     OWSAssertDebug(messageSend);
     OWSAssertDebug(messageSend.thread || [messageSend.message isKindOfClass:[OWSOutgoingSyncMessage class]]);
+    NSString *userPublicKey = OWSIdentityManager.sharedManager.identityKeyPair.hexEncodedPublicKey;
+    OWSAssertDebug(messageSend.isUDSend || [messageSend.recipient.recipientId isEqual:userPublicKey]);
 
     TSOutgoingMessage *message = messageSend.message;
     SignalRecipient *recipient = messageSend.recipient;