fix: 修复 _email_poller 线程静默死亡问题

- IMAP 连接加 30s socket timeout，防止 _send_id_command 等操作永久阻塞
- _email_poller 加顶层 try/except，异常后 sleep 5s 继续循环
- @retry() 加指数退避延迟(1s,2s,4s...)，避免重试风暴

main.py

@@ -45,6 +45,7 @@ def _signal_handler(signum, frame):
 def _email_poller(cfg):
     logger.info("邮件轮询线程已启动")
     while _running:
+        try:
             for acct_idx, mail in poll_accounts(cfg):
                 if not _running:
                     return
@@ -52,6 +53,9 @@ def _email_poller(cfg):
                     if mail.uid not in _pending_uids:
                         _pending_uids.add(mail.uid)
                         _email_queue.put((acct_idx, mail))
+        except Exception as e:
+            logger.error(f"邮件轮询线程异常: {e}", exc_info=True)
+            time.sleep(5)
         if _running:
             for _ in range(cfg.polling.interval_seconds):
                 if not _running:

src/email_client.py

@@ -87,12 +87,12 @@ def _select_mailbox(conn, mailbox: str = "INBOX"):
         raise RuntimeError(f"无法选择邮箱 {mailbox}: {data}")
 
 
-def _login_and_prepare(account: EmailAccount):
-    logger.info("连接 %s:%d", account.imap_server, account.imap_port)
+def _login_and_prepare(account: EmailAccount, timeout: int = 30):
+    logger.info("连接 %s:%d (超时%ds)", account.imap_server, account.imap_port, timeout)
     if account.use_ssl:
-        conn = imaplib.IMAP4_SSL(account.imap_server, account.imap_port)
+        conn = imaplib.IMAP4_SSL(account.imap_server, account.imap_port, timeout=timeout)
     else:
-        conn = imaplib.IMAP4(account.imap_server, account.imap_port)
+        conn = imaplib.IMAP4(account.imap_server, account.imap_port, timeout=timeout)
         if account.use_starttls:
             conn.starttls()
     conn.login(account.username, account.password)

src/retry.py

@@ -1,10 +1,11 @@
 import logging
+import time
 from functools import wraps
 
 logger = logging.getLogger(__name__)
 
 
-def retry(max_tries=10):
+def retry(max_tries=10, base_delay=1, max_delay=60):
     def decorator(func):
         @wraps(func)
         def wrapper(*args, **kwargs):
@@ -15,10 +16,12 @@ def retry(max_tries=10):
                 except Exception as e:
                     last_exc = e
                     if attempt < max_tries:
+                        delay = min(base_delay * (2 ** (attempt - 1)), max_delay)
                         logger.warning(
-                            "%s 失败(第%d次)，正在重试: %s",
-                            func.__name__, attempt, e,
+                            "%s 失败(第%d次)，%d秒后重试: %s",
+                            func.__name__, attempt, delay, e,
                         )
+                        time.sleep(delay)
                     else:
                         logger.error(
                             "%s 失败 %d 次，放弃: %s",