fix: default type to 'transfer' for TSS sendMany requests

MPC sendMany requires the type parameter for TSS wallets but the schema
marks it as optional. This defaults type to 'transfer' when not provided,
matching the actual SDK requirement.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: pranavjain97

src/__tests__/api/master/sendMany.test.ts

@@ -298,6 +298,10 @@ describe('POST /api/v1/:coin/advancedwallet/:walletId/sendMany', () => {
       response.body.should.have.property('txid', 'test-tx-id');
       response.body.should.have.property('tx', 'signed-transaction');
 
+      // Verify that type defaults to 'transfer' for TSS wallets when not provided
+      const sendManyArgs = sendManyStub.firstCall.args[0] as Record<string, unknown>;
+      sendManyArgs.should.have.property('type', 'transfer');
+
       walletGetNock.done();
       keychainGetNock.done();
       sinon.assert.calledOnce(sendManyStub);

src/masterBitgoExpress/handlers/handleSendMany.ts

@@ -125,6 +125,10 @@ export async function handleSendMany(req: MasterApiSpecRouteRequest<'v1.wallet.s
       if (signingKeychain.source === 'backup') {
         throw new BadRequestError('Backup MPC signing not supported for sendMany');
       }
+      // TSS wallets require type to be set; default to 'transfer' if not provided
+      if (!params.type) {
+        params.type = 'transfer';
+      }
       const mpcSendParams = await createMPCSendParamsWithCustomSigningFns(
         req,
         awmClient,

src/masterBitgoExpress/routers/sendManyRoute.ts

@@ -8,7 +8,7 @@ export const SendManyRequest = {
    */
   source: t.union([t.literal('user'), t.literal('backup')]),
   /**
-   * Required for transactions from MPC wallets.
+   * Required for transactions from MPC wallets. Defaults to 'transfer' for TSS wallets if not provided.
    */
   type: t.union([
     t.undefined,