test(sdk-coin-dot): cover missing userKey/backupKey guard clauses

Add regression tests for the missing-userKey and missing-backupKey
guards in isMpcv2SigningMaterial(), which were introduced in the
previous commit but had no dedicated coverage. Without these, a
regression to the guard order or message would surface as a
confusing downstream decrypt/parse error instead of the intended
clear validation error.

Ticket: WCI-1236
Session-Id: 851002b4-f316-42fd-a2ea-f9189b46e8a9
Task-Id: d2ffc5e1-d6cc-4c7d-8e3e-be446e5dc185

Author: vibhavgo

modules/sdk-coin-dot/test/unit/dot.ts

@@ -525,6 +525,28 @@ describe('DOT:', function () {
         .should.be.rejectedWith('EdDSA MPCv2 recovery: commonKeyChain from keycard does not match bitgoKey');
     });
 
+    it('should throw missing userKey when walletPassphrase is set but userKey is omitted', async function () {
+      await basecoin
+        .recover({
+          backupKey: mpcV2BackupKey,
+          bitgoKey: mpcV2CommonKeyChain,
+          walletPassphrase,
+          recoveryDestination: destAddr,
+        })
+        .should.be.rejectedWith('missing userKey');
+    });
+
+    it('should throw missing backupKey when walletPassphrase is set but backupKey is omitted', async function () {
+      await basecoin
+        .recover({
+          userKey: mpcV2UserKey,
+          bitgoKey: mpcV2CommonKeyChain,
+          walletPassphrase,
+          recoveryDestination: destAddr,
+        })
+        .should.be.rejectedWith('missing backupKey');
+    });
+
     it('should skip keycard decryption when multisigTypeVersion is pre-resolved to MPCv2', async function () {
       const isMpcv2Spy = sandBox.spy(Dot.prototype, 'isMpcv2SigningMaterial' as keyof Dot);