Update error message and add assertion

Author: FrederikBolding

packages/snaps-controllers/coverage.json

@@ -1,6 +1,6 @@
 {
-  "branches": 93.26,
+  "branches": 93.28,
   "functions": 96.79,
-  "lines": 98.14,
-  "statements": 97.87
+  "lines": 98.15,
+  "statements": 97.88
 }

packages/snaps-controllers/src/multichain/MultichainRouter.test.ts

@@ -266,7 +266,7 @@ describe('MultichainRouter', () => {
             },
           },
         }),
-      ).rejects.toThrow('Invalid method parameter(s)');
+      ).rejects.toThrow('No available account found for request.');
     });
   });
 

packages/snaps-controllers/src/multichain/MultichainRouter.ts

@@ -13,7 +13,7 @@ import type {
   CaipChainId,
   JsonRpcParams,
 } from '@metamask/utils';
-import { hasProperty, parseCaipAccountId } from '@metamask/utils';
+import { assert, hasProperty, parseCaipAccountId } from '@metamask/utils';
 
 import { getRunnableSnaps } from '../snaps';
 import type { GetAllSnaps, HandleSnapRequest } from '../snaps';
@@ -225,7 +225,9 @@ export class MultichainRouter {
     );
 
     if (!selectedAccount) {
-      throw rpcErrors.invalidParams();
+      throw rpcErrors.invalidParams({
+        message: 'No available account found for request.',
+      });
     }
 
     return selectedAccount.id;
@@ -288,6 +290,9 @@ export class MultichainRouter {
     scope: CaipChainId;
     request: JsonRpcRequest;
   }): Promise<unknown> {
+    // Explicitly block EVM scopes, just in case.
+    assert(!scope.startsWith('eip155') && !scope.startsWith('wallet:eip155'));
+
     const { method, params } = request;
 
     // If the RPC request can be serviced by an account Snap, route it there.