fix(http): 支持默认HTTP客户端原子重建以恢复HTTP/2流容量

feat(db): 为外键列补充缺失的数据库索引并添加迁移脚本

- HTTPClientPool._reset_default_client 原子替换共享客户端，旧客户端在宽限期后异步关闭
- reset_upstream_client 对无代理路由不再直接跳过，改为调用 _reset_default_client
- 为 Usage, WalletTransaction, PaymentCallback, RefundRequest, VideoTask, RequestCandidate 等表的外键列添加 index=True

src/clients/http_client.py

@@ -54,6 +54,8 @@ class HTTPClientPool:
     _max_proxy_clients: int = 50
     # Tunnel 客户端缓存：{node_id: client}
     _tunnel_clients: dict[str, httpx.AsyncClient] = {}
+    # 后台清理任务引用集合（防止被 GC 回收）
+    _background_tasks: set[asyncio.Task[None]] = set()
 
     def __new__(cls) -> "HTTPClientPool":
         if cls._instance is None:
@@ -457,6 +459,51 @@ class HTTPClientPool:
         client_config.update(kwargs)
         return httpx.AsyncClient(**client_config)  # type: ignore[arg-type]
 
+    @classmethod
+    async def _reset_default_client(cls) -> bool:
+        """Atomically replace the shared default client with a fresh instance.
+
+        The old client is kept open briefly so that in-flight requests can
+        finish on their existing HTTP/2 streams; it is closed asynchronously
+        after a short grace period.
+        """
+        async with _default_client_lock:
+            old_client = cls._default_client
+            if old_client is None:
+                return False
+
+            # Create a new client before discarding the old one
+            cls._default_client = httpx.AsyncClient(
+                http2=config.enable_http2,
+                verify=get_ssl_context(),
+                timeout=httpx.Timeout(
+                    connect=config.http_connect_timeout,
+                    read=config.http_read_timeout,
+                    write=config.http_write_timeout,
+                    pool=config.http_pool_timeout,
+                ),
+                limits=httpx.Limits(
+                    max_connections=config.http_max_connections,
+                    max_keepalive_connections=config.http_keepalive_connections,
+                    keepalive_expiry=config.http_keepalive_expiry,
+                ),
+                follow_redirects=True,
+            )
+
+        # Close old client after a grace period so in-flight requests can drain
+        async def _close_old() -> None:
+            await asyncio.sleep(5)
+            try:
+                await old_client.aclose()
+            except Exception as exc:
+                logger.warning("关闭旧默认客户端失败: {}", exc)
+
+        task = asyncio.create_task(_close_old())
+        cls._background_tasks.add(task)
+        task.add_done_callback(cls._background_tasks.discard)
+        logger.warning("默认HTTP客户端已重建(HTTP/2 流容量恢复)")
+        return True
+
     @classmethod
     async def reset_upstream_client(
         cls,
@@ -467,8 +514,9 @@ class HTTPClientPool:
         """Reset cached upstream client for the given proxy/tunnel route.
 
         Returns True when a cached client was closed and removed.
-        For the shared no-proxy default client this is a no-op to avoid
-        disrupting unrelated in-flight requests.
+        For the shared no-proxy default client, atomically replaces it with a
+        new instance so that subsequent requests get a fresh HTTP/2 connection
+        while in-flight requests on the old client can finish naturally.
         """
         if delegate_cfg and delegate_cfg.get("tunnel"):
             node_id = str(delegate_cfg.get("node_id") or "")
@@ -490,7 +538,7 @@ class HTTPClientPool:
 
         base_cache_key = compute_proxy_cache_key(proxy_config)
         if base_cache_key == "__no_proxy__":
-            return False
+            return await cls._reset_default_client()
 
         cache_key_prefixes = [base_cache_key]
         tls_profile_key = str(tls_profile or "").strip().lower()