fix: deriveTransactionType defaults to CustomTx for non-transfer transactions

deriveTransactionType previously fell through to Send for any transaction
that didn't match a known staking or ATA pattern. This misclassified
custom transactions (e.g. boilerplate-only Memo+NonceAdvance txs) as Send.

Explicitly check for Transfer/TokenTransfer instructions before returning
Send. Everything else falls through to CustomTx, matching the legacy
getTransactionType behavior.

BTC-3102

Author: lcovar

modules/sdk-coin-sol/src/lib/explainTransactionWasm.ts

@@ -112,7 +112,11 @@ function deriveTransactionType(
   // Unknown instructions indicate a custom/unrecognized transaction
   if (instructions.some((i) => i.type === 'Unknown')) return TransactionType.CustomTx;
 
-  return TransactionType.Send;
+  // Send requires an explicit Transfer or TokenTransfer instruction.
+  // Everything else is a custom/unrecognized transaction.
+  if (instructions.some((i) => i.type === 'Transfer' || i.type === 'TokenTransfer')) return TransactionType.Send;
+
+  return TransactionType.CustomTx;
 }
 
 // =============================================================================

modules/sdk-coin-sol/test/unit/explainTransactionWasm.ts

@@ -0,0 +1,27 @@
+/**
+ * Tests for explainTransactionWasm (WASM-based Solana transaction explanation).
+ */
+import 'should';
+import { explainSolTransaction } from '../../src/lib/explainTransactionWasm';
+
+describe('explainTransactionWasm', function () {
+  describe('deriveTransactionType', function () {
+    it('should classify boilerplate-only transaction as CustomTx', function () {
+      // Transaction with only NonceAdvance + Memo instructions (no Transfer or TokenTransfer).
+      // Previously this would incorrectly fall through to 'Send'.
+      const BOILERPLATE_ONLY_TX_BASE64 =
+        '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';
+
+      const explained = explainSolTransaction({
+        txBase64: BOILERPLATE_ONLY_TX_BASE64,
+        feeInfo: { fee: '5000' },
+        coinName: 'tsol',
+      });
+
+      explained.type.should.equal('CustomTx');
+      explained.outputAmount.should.equal('0');
+      explained.outputs.length.should.equal(0);
+      (typeof explained.memo).should.equal('string');
+    });
+  });
+});