fix(electron): add gRPC connection check before subscribing to messages

The app was crashing with "CANCELLED: Cancelled on client" error when
opening the app a second time. This happened because:

1. When window was reopened, old gRPC streams were in cancelled state
2. prepareForSign/prepareForKeygen tried to subscribe on cancelled streams
3. The error was unhandled and crashed the app

Changes:
- Add isConnected() check in prepareForSign() and prepareForKeygen()
- Throw meaningful error when gRPC client is not connected
- Wrap all prepareFor* calls in try-catch in main.ts
- Return user-friendly error message instead of crashing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/mpc-system/services/service-party-app/electron/main.ts

@@ -1174,8 +1174,13 @@ function setupIpcHandlers() {
         // 这确保在其他方开始发送 TSS 消息时，我们已经准备好接收和缓冲
         // 即使 keygen 进程还没启动，消息也不会丢失
         if (tssHandler && 'prepareForKeygen' in tssHandler) {
-          debugLog.info('tss', `Preparing for keygen: subscribing to messages for session ${sessionId}`);
+          try {
-          (tssHandler as { prepareForKeygen: (sessionId: string, partyId: string) => void }).prepareForKeygen(sessionId, partyId);
+            debugLog.info('tss', `Preparing for keygen: subscribing to messages for session ${sessionId}`);
+            (tssHandler as { prepareForKeygen: (sessionId: string, partyId: string) => void }).prepareForKeygen(sessionId, partyId);
+          } catch (prepareErr) {
+            debugLog.error('tss', `Failed to prepare for keygen: ${(prepareErr as Error).message}`);
+            return { success: false, error: `消息订阅失败: ${(prepareErr as Error).message}` };
+          }
         }
 
         // 方案 B: 检查 JoinSession 响应中的 session 状态
@@ -1287,8 +1292,13 @@ function setupIpcHandlers() {
 
           // 关键步骤：立即预订阅消息流
           if (tssHandler && 'prepareForKeygen' in tssHandler) {
-            debugLog.info('tss', `Initiator preparing for keygen: subscribing to messages for session ${result.session_id}`);
+            try {
-            (tssHandler as { prepareForKeygen: (sessionId: string, partyId: string) => void }).prepareForKeygen(result.session_id, partyId);
+              debugLog.info('tss', `Initiator preparing for keygen: subscribing to messages for session ${result.session_id}`);
+              (tssHandler as { prepareForKeygen: (sessionId: string, partyId: string) => void }).prepareForKeygen(result.session_id, partyId);
+            } catch (prepareErr) {
+              debugLog.error('tss', `Failed to prepare for keygen: ${(prepareErr as Error).message}`);
+              return { success: false, error: `消息订阅失败: ${(prepareErr as Error).message}` };
+            }
           }
 
           // 方案 B: 检查 JoinSession 响应中的 session 状态
@@ -1707,8 +1717,13 @@ function setupIpcHandlers() {
 
           // 预订阅消息流
           if (tssHandler && 'prepareForSign' in tssHandler) {
-            debugLog.info('tss', `Initiator preparing for sign: subscribing to messages for session ${result.session_id}`);
+            try {
-            (tssHandler as TSSHandler).prepareForSign(result.session_id, partyId);
+              debugLog.info('tss', `Initiator preparing for sign: subscribing to messages for session ${result.session_id}`);
+              (tssHandler as TSSHandler).prepareForSign(result.session_id, partyId);
+            } catch (prepareErr) {
+              debugLog.error('tss', `Failed to prepare for sign: ${(prepareErr as Error).message}`);
+              return { success: false, error: `消息订阅失败: ${(prepareErr as Error).message}` };
+            }
           }
 
           // 检查会话状态
@@ -1873,8 +1888,13 @@ function setupIpcHandlers() {
 
         // 预订阅消息流
         if (tssHandler && 'prepareForSign' in tssHandler) {
-          debugLog.info('tss', `Preparing for sign: subscribing to messages for session ${params.sessionId}`);
+          try {
-          (tssHandler as TSSHandler).prepareForSign(params.sessionId, partyId);
+            debugLog.info('tss', `Preparing for sign: subscribing to messages for session ${params.sessionId}`);
+            (tssHandler as TSSHandler).prepareForSign(params.sessionId, partyId);
+          } catch (prepareErr) {
+            debugLog.error('tss', `Failed to prepare for sign: ${(prepareErr as Error).message}`);
+            return { success: false, error: `消息订阅失败: ${(prepareErr as Error).message}` };
+          }
         }
 
         // 检查会话状态

backend/mpc-system/services/service-party-app/electron/modules/tss-handler.ts

@@ -123,6 +123,12 @@ export class TSSHandler extends EventEmitter {
    * @param partyId 自己的 party ID
    */
   prepareForKeygen(sessionId: string, partyId: string): void {
+    // 检查 gRPC 连接状态
+    if (!this.grpcClient.isConnected()) {
+      console.error('[TSS] Cannot prepare for keygen: gRPC client not connected');
+      throw new Error('gRPC client not connected');
+    }
+
     // 如果已经为同一个 session 准备过，跳过
     if (this.isPrepared && this.sessionId === sessionId) {
       console.log('[TSS] Already prepared for same session, skip');
@@ -489,6 +495,12 @@ export class TSSHandler extends EventEmitter {
    * @param partyId 自己的 party ID
    */
   prepareForSign(sessionId: string, partyId: string): void {
+    // 检查 gRPC 连接状态
+    if (!this.grpcClient.isConnected()) {
+      console.error('[TSS-SIGN] Cannot prepare for sign: gRPC client not connected');
+      throw new Error('gRPC client not connected');
+    }
+
     // 如果已经为同一个 session 准备过，跳过
     if (this.isPrepared && this.sessionId === sessionId) {
       console.log('[TSS-SIGN] Already prepared for same session, skip');