Enhance error handling in RPC functions for clearer messages

packages/brain/src/modules/apiServers/ui/startUiServer.ts

@@ -30,6 +30,17 @@ interface RpcRequest {
   id: string | number | null;
 }
 
+function toRpcErrorMessage(error: unknown): string {
+  if (error == null) return "Unknown error";
+  if (typeof error === "string") return error;
+  if (error instanceof Error) return error.message || error.name || "Unknown error";
+  try {
+    return JSON.stringify(error);
+  } catch {
+    return String(error);
+  }
+}
+
 export function startUiServer({
   brainDb,
   blockExplorerApi,
@@ -101,7 +112,7 @@ export function startUiServer({
         logger.error(error);
         callback({
           jsonrpc: "2.0",
-          error: { code: -32601, message: error },
+          error: { code: -32601, message: toRpcErrorMessage(error) },
           id
         });
       }

packages/ui/src/socket/socket.ts

@@ -2,6 +2,40 @@ import { io, Socket } from "socket.io-client";
 import { RoutesArguments, RoutesReturn, RpcMethodNames } from "./types.js";
 import { BRAIN_UI_DOMAIN, Network } from "@stakingbrain/common";
 
+function toErrorMessage(value: unknown): string {
+  if (value == null) return "Unknown error";
+  if (typeof value === "string") return value;
+  if (value instanceof Error) return value.message || value.name || "Unknown error";
+
+  if (typeof value === "object") {
+    const record = value as Record<string, unknown>;
+    // Common JSON-RPC shape: { code, message, data }
+    const message = record.message;
+
+    if (typeof message === "string") return message;
+    if (message instanceof Error) return message.message || message.name || "Unknown error";
+
+    // In this repo the backend currently sends `message: error` where error can be an object.
+    if (message && typeof message === "object") {
+      const nested = message as Record<string, unknown>;
+      if (typeof nested.message === "string") return nested.message;
+      try {
+        return JSON.stringify(message);
+      } catch {
+        return String(message);
+      }
+    }
+
+    try {
+      return JSON.stringify(value);
+    } catch {
+      return String(value);
+    }
+  }
+
+  return String(value);
+}
+
 class RpcClient {
   private socket: Socket;
 
@@ -33,7 +67,10 @@ class RpcClient {
       // eslint-disable-next-line @typescript-eslint/no-explicit-any
       this.socket.emit("rpc", rpcRequest, (response: any) => {
         if (response.error) {
-          reject(response.error);
+          const err = new Error(toErrorMessage(response.error));
+          // Preserve the raw JSON-RPC error payload for debugging if needed.
+          (err as Error & { rpcError?: unknown }).rpcError = response.error;
+          reject(err);
         } else {
           resolve(response.result as RoutesReturn[T]);
         }