feat(service-party-app): 验证成功后自动加入会话

- 移除手动输入名称和点击"确认加入"按钮的步骤
- 验证邀请码成功后自动触发 joinSession
- 生成默认参与者名称（参与者-xxxx 格式）
- 保留错误处理和重试功能
- 减少用户操作步骤，提高 co_managed_keygen 可靠性

🤖 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/src/pages/Join.tsx

@@ -12,6 +12,12 @@ interface SessionInfo {
   totalParticipants?: number;
 }
 
+// 生成默认参与者名称
+function generateParticipantName(): string {
+  const timestamp = Date.now().toString(36).slice(-4);
+  return `参与者-${timestamp}`;
+}
+
 interface ValidateResult {
   success: boolean;
   error?: string;
@@ -24,13 +30,14 @@ export default function Join() {
   const navigate = useNavigate();
 
   const [code, setCode] = useState(inviteCode || '');
-  const [participantName, setParticipantName] = useState('');
+  const [participantName] = useState(generateParticipantName());
   const [isLoading, setIsLoading] = useState(false);
   const [error, setError] = useState<string | null>(null);
   const [sessionInfo, setSessionInfo] = useState<SessionInfo | null>(null);
   const [joinToken, setJoinToken] = useState<string | null>(null);
   const [partyId, setPartyId] = useState<string | null>(null);
   const [step, setStep] = useState<'input' | 'confirm' | 'joining'>('input');
+  const [autoJoinAttempted, setAutoJoinAttempted] = useState(false);
 
   useEffect(() => {
     if (inviteCode) {
@@ -38,6 +45,22 @@ export default function Join() {
     }
   }, [inviteCode]);
 
+  // 自动加入：验证成功后自动加入会话
+  useEffect(() => {
+    if (
+      step === 'confirm' &&
+      sessionInfo &&
+      joinToken &&
+      partyId &&
+      participantName &&
+      !autoJoinAttempted &&
+      !isLoading
+    ) {
+      setAutoJoinAttempted(true);
+      handleJoinSession();
+    }
+  }, [step, sessionInfo, joinToken, partyId, participantName, autoJoinAttempted, isLoading]);
+
   const handleValidateCode = async (codeToValidate: string) => {
     if (!codeToValidate.trim()) {
       setError('请输入邀请码');
@@ -76,8 +99,8 @@ export default function Join() {
   };
 
   const handleJoinSession = async () => {
-    if (!sessionInfo || !participantName.trim()) {
-      setError('请输入参与者名称');
+    if (!sessionInfo) {
+      setError('会话信息不完整');
       return;
     }
 
@@ -204,42 +227,42 @@ export default function Join() {
               </div>
             </div>
 
-            <div className={styles.inputGroup}>
-              <label className={styles.label}>您的名称</label>
-              <input
-                type="text"
-                value={participantName}
-                onChange={(e) => setParticipantName(e.target.value)}
-                placeholder="输入您的名称（其他参与者可见）"
-                className={styles.input}
-                disabled={isLoading}
-              />
-            </div>
-
-            {error && <div className={styles.error}>{error}</div>}
-
-            <div className={styles.actions}>
-              <button
-                className={styles.secondaryButton}
-                onClick={() => {
-                  setStep('input');
-                  setSessionInfo(null);
-                  setJoinToken(null);
-                  setPartyId(null);
-                  setError(null);
-                }}
-                disabled={isLoading}
-              >
-                返回
-              </button>
-              <button
-                className={styles.primaryButton}
-                onClick={handleJoinSession}
-                disabled={isLoading || !participantName.trim()}
-              >
-                {isLoading ? '加入中...' : '确认加入'}
-              </button>
-            </div>
+            {error ? (
+              <>
+                <div className={styles.error}>{error}</div>
+                <div className={styles.actions}>
+                  <button
+                    className={styles.secondaryButton}
+                    onClick={() => {
+                      setStep('input');
+                      setSessionInfo(null);
+                      setJoinToken(null);
+                      setPartyId(null);
+                      setError(null);
+                      setAutoJoinAttempted(false);
+                    }}
+                    disabled={isLoading}
+                  >
+                    返回
+                  </button>
+                  <button
+                    className={styles.primaryButton}
+                    onClick={() => {
+                      setAutoJoinAttempted(false);
+                      setError(null);
+                    }}
+                    disabled={isLoading}
+                  >
+                    重试
+                  </button>
+                </div>
+              </>
+            ) : (
+              <div className={styles.joining}>
+                <div className={styles.spinner}></div>
+                <p>正在自动加入会话...</p>
+              </div>
+            )}
           </div>
         )}