require the policy line and check the declared cosigner count when importing coldcard format multisig wallets

src/main/java/com/sparrowwallet/sparrow/io/ColdcardMultisig.java

@@ -121,7 +121,8 @@ public class ColdcardMultisig implements WalletImport, KeystoreFileImport, Walle
         Wallet wallet = new Wallet();
         wallet.setPolicyType(PolicyType.MULTI_HD);
 
-        int threshold = 2;
+        int threshold = 0;
+        int cosigners = 0;
         ScriptType scriptType = ScriptType.P2SH;
         String derivation = null;
 
@@ -143,7 +144,12 @@ public class ColdcardMultisig implements WalletImport, KeystoreFileImport, Walle
                             wallet.setName(value.trim());
                             break;
                         case "Policy":
-                            threshold = Integer.parseInt(value.split(" ")[0]);
+                            String[] policy = value.split("\\s+");
+                            if(policy.length != 3) {
+                                throw new IllegalStateException("Could not determine the multisig policy from \"" + line + "\"");
+                            }
+                            threshold = Integer.parseInt(policy[0]);
+                            cosigners = Integer.parseInt(policy[2]);
                             break;
                         case "Derivation":
                         case "# derivation":
@@ -167,8 +173,16 @@ public class ColdcardMultisig implements WalletImport, KeystoreFileImport, Walle
             }
 
 
-            Policy policy = Policy.getPolicy(PolicyType.MULTI_HD, scriptType, wallet.getKeystores(), threshold);
-            wallet.setDefaultPolicy(policy);
+            if(threshold == 0) {
+                throw new IllegalStateException("This file does not specify the multisig policy");
+            }
+
+            if(cosigners != wallet.getKeystores().size()) {
+                throw new IllegalStateException("This file specifies a policy of " + threshold + " of " + cosigners + ", but contains " + wallet.getKeystores().size() + " cosigner key" + (wallet.getKeystores().size() == 1 ? "" : "s"));
+            }
+
+            Policy walletPolicy = Policy.getPolicy(PolicyType.MULTI_HD, scriptType, wallet.getKeystores(), threshold);
+            wallet.setDefaultPolicy(walletPolicy);
             wallet.setScriptType(scriptType);
 
             try {

src/test/java/com/sparrowwallet/sparrow/io/ColdcardMultisigTest.java

@@ -99,6 +99,18 @@ public class ColdcardMultisigTest extends IoTest {
         Assertions.assertTrue(wallet.isValid());
     }
 
+    @Test
+    public void importWalletMissingPolicy() {
+        ColdcardMultisig ccMultisig = new ColdcardMultisig();
+        Assertions.assertThrows(ImportException.class, () -> ccMultisig.importWallet(getInputStream("cc-multisig-export-nopolicy.txt"), null));
+    }
+
+    @Test
+    public void importWalletMissingCosigner() {
+        ColdcardMultisig ccMultisig = new ColdcardMultisig();
+        Assertions.assertThrows(ImportException.class, () -> ccMultisig.importWallet(getInputStream("cc-multisig-export-missingkey.txt"), null));
+    }
+
     @Test
     public void exportWallet1() throws ImportException, ExportException, IOException {
         ColdcardMultisig ccMultisig = new ColdcardMultisig();

src/test/resources/com/sparrowwallet/sparrow/io/cc-multisig-export-missingkey.txt

@@ -0,0 +1,10 @@
+# Coldcard Multisig setup file (created on 0F056943)
+#
+Name: CC-2-of-4
+Policy: 2 of 4
+Derivation: m/48'/0'/0'/2'
+Format: P2WSH
+
+0F056943: xpub6EfEGa5isJbQFSswM5Uptw5BSq2Td1ZDJr3QUNUcMySpC7itZ3ccypVHtLPnvMzKQ2qxrAgH49vhVxRcaQLFbixAVRR8RACrYTp88Uv9h8Z
+6BA6CFD0: xpub6FFEQVG6QR28giDuML74Y7EMPwqEiKftNjScLzg5WKM41bf6LMP2XspjBgNp28tvkNUZdokmTY4TcRbuGZBSMvNoUECrKW1y3TBPeQJVmAg
+747B698E: xpub6Eb6Z1xtmWRiWKgRpHf6dHiEagGd6FLiBXrnma1nFK4PGRYqSVqVyJaxna5Mb8etSP4ATKVAvKnXG1a9HZauoAawuSDJT5RgH2HqEVHZVHY

src/test/resources/com/sparrowwallet/sparrow/io/cc-multisig-export-nopolicy.txt

@@ -0,0 +1,13 @@
+# Exported from Electrum
+Name: el-CC-3-of-3-sb-2
+Format: P2WSH
+
+Derivation: m/48'/0'/0'/2'
+06B57041: xpub6EfEGa5isJbQFSswM5Uptw5BSq2Td1ZDJr3QUNUcMySpC7itZ3ccypVHtLPnvMzKQ2qxrAgH49vhVxRcaQLFbixAVRR8RACrYTp88Uv9h8Z
+
+Derivation: m/48'/0'/0'/2'
+4B569672: xpub6FFEQVG6QR28giDuML74Y7EMPwqEiKftNjScLzg5WKM41bf6LMP2XspjBgNp28tvkNUZdokmTY4TcRbuGZBSMvNoUECrKW1y3TBPeQJVmAg
+
+Derivation: m/47'/0'/0'/1'
+CA9A2B19: xpub6Eb6Z1xtmWRiWKgRpHf6dHiEagGd6FLiBXrnma1nFK4PGRYqSVqVyJaxna5Mb8etSP4ATKVAvKnXG1a9HZauoAawuSDJT5RgH2HqEVHZVHY
+