rpc: send: support external signer

src/util/error.cpp

@@ -31,6 +31,10 @@ bilingual_str TransactionErrorString(const TransactionError err)
             return Untranslated("Specified sighash value does not match value stored in PSBT");
         case TransactionError::MAX_FEE_EXCEEDED:
             return Untranslated("Fee exceeds maximum configured by user (e.g. -maxtxfee, maxfeerate)");
+        case TransactionError::EXTERNAL_SIGNER_NOT_FOUND:
+            return Untranslated("External signer not found");
+        case TransactionError::EXTERNAL_SIGNER_FAILED:
+            return Untranslated("External signer failed to sign");
         // no default case, so the compiler can warn about missing cases
     }
     assert(false);

src/util/error.h

@@ -30,6 +30,8 @@ enum class TransactionError {
     PSBT_MISMATCH,
     SIGHASH_MISMATCH,
     MAX_FEE_EXCEEDED,
+    EXTERNAL_SIGNER_NOT_FOUND,
+    EXTERNAL_SIGNER_FAILED,
 };
 
 bilingual_str TransactionErrorString(const TransactionError error);