sync selected fiat currency

app/core/Engine/Engine.ts

@@ -197,6 +197,7 @@ import { removeAccountsFromPermissions } from '../Permissions';
 import { keyringSnapPermissionsBuilder } from '../SnapKeyring/keyringSnapsPermissions';
 import { createMultichainBalancesController } from './controllers/MultichainBalancesController/utils';
 import { createMultichainRatesController } from './controllers/RatesController/utils';
+import { setupCurrencyRateSync } from './controllers/RatesController/subscriptions';
 ///: END:ONLY_INCLUDE_IF
 ///: BEGIN:ONLY_INCLUDE_IF(preinstalled-snaps,external-snaps)
 import { HandleSnapRequestArgs } from '../Snaps/types';
@@ -413,6 +414,9 @@ export class Engine {
       messenger: multichainRatesControllerMessenger,
       initialState: initialState.RatesController,
     });
+
+    // Set up currency rate sync
+    setupCurrencyRateSync(this.controllerMessenger, multichainRatesController);
     ///: END:ONLY_INCLUDE_IF
 
     const nftController = new NftController({

app/core/Engine/controllers/RatesController/subscriptions.ts

@@ -0,0 +1,37 @@
+import {
+  RatesController,
+  CurrencyRateState,
+  CurrencyRateController,
+} from '@metamask/assets-controllers';
+import Logger from '../../../../util/Logger';
+
+/**
+ * Sets up subscription to sync CurrencyRateController changes with RatesController
+ * @param controllerMessenger - The main controller messenger
+ * @param ratesController - The RatesController instance to sync with
+ */
+export const setupCurrencyRateSync = (
+  controllerMessenger: {
+    subscribe: (
+      eventName: string,
+      handler: (state: CurrencyRateState) => void,
+    ) => void;
+  },
+  ratesController: RatesController,
+): void => {
+  controllerMessenger.subscribe(
+    `${CurrencyRateController.name}:stateChange`,
+    (state: CurrencyRateState) => {
+      if (state.currentCurrency) {
+        ratesController
+          .setFiatCurrency(state.currentCurrency)
+          .catch((error) => {
+            Logger.error(
+              error as Error,
+              'RatesController: Failed to sync fiat currency with CurrencyRateController',
+            );
+          });
+      }
+    },
+  );
+};

app/core/Engine/controllers/RatesController/utils.ts

@@ -2,6 +2,7 @@ import {
   RatesController,
   RatesControllerState,
   RatesControllerMessenger,
+  CurrencyRateState,
 } from '@metamask/assets-controllers';
 import Logger from '../../../../util/Logger';
 
@@ -25,6 +26,7 @@ export const createMultichainRatesController = ({
       state: initialState ?? {},
       includeUsdRate: true,
     });
+
     return multichainRatesController;
   } catch (error) {
     Logger.error(error as Error, 'Failed to initialize RatesController');