fix: 代码验证发现的两处问题

- websocket.py: asyncio.get_event_loop() → get_running_loop()
  (Python 3.10+废弃，shutdown时可能RuntimeError)
- asyncssh_pool.py: 全忙等待逻辑在锁外操作有竞态条件
  简化为直接raise ConnectionError，不在锁外重试

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

server/api/websocket.py

@@ -60,9 +60,11 @@ class ConnectionManager:
         if conn:
             # Close the WebSocket to release the TCP connection
             try:
-                asyncio.get_event_loop().create_task(
+                asyncio.get_running_loop().create_task(
                     conn["websocket"].close(code=1000, reason="cleanup")
                 )
+            except RuntimeError:
+                pass  # No running event loop (e.g. during shutdown)
             except Exception:
                 pass
             logger.info(f"WebSocket disconnected: {client_id}, total: {len(self._connections)}")

server/infrastructure/ssh/asyncssh_pool.py

@@ -98,28 +98,15 @@ class AsyncSSHPool:
                 logger.debug(f"Reused SSH connection: server={server.id}, refs={pooled.ref_count}")
                 return pooled.conn
 
-            # Need to create — evict if at capacity, then release lock for handshake
+            # Need to create — evict if at capacity
             if len(self._pool) >= self.MAX_CONNECTIONS:
                 evicted = await self._evict_one()
                 if not evicted:
-                    # All connections are busy — wait for one to be released, then retry
-                    logger.warning(f"SSH pool at capacity ({self.MAX_CONNECTIONS}), all busy — waiting")
-
-        # If pool was full and all busy, wait briefly for a release before creating
-        if len(self._pool) >= self.MAX_CONNECTIONS:
-            for _ in range(3):  # Wait up to 3 × 2s = 6s
-                await asyncio.sleep(2)
-                async with self._lock:
-                    if len(self._pool) < self.MAX_CONNECTIONS:
-                        break
-                    await self._evict_one()
-                    if len(self._pool) < self.MAX_CONNECTIONS:
-                        break
-            else:
-                raise ConnectionError(
-                    f"SSH pool at capacity ({self.MAX_CONNECTIONS}) and all connections busy. "
-                    f"Try again later."
-                )
+                    # All connections are busy — cannot exceed MAX_CONNECTIONS
+                    raise ConnectionError(
+                        f"SSH pool at capacity ({self.MAX_CONNECTIONS}) and all connections busy. "
+                        f"Try again later."
+                    )
 
         # Create connection outside lock (handshake can take seconds)
         conn = await self._create_connection(server)