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

alembic/versions/20260307_1628_2d932114930d_add_missing_foreign_key_indexes_for_.py

@@ -0,0 +1,80 @@
+"""add missing foreign key indexes for cascade delete performance
+
+Revision ID: 2d932114930d
+Revises: 8e71f2a4c9b0
+Create Date: 2026-03-07 16:28:48.633531+00:00
+
+"""
+from alembic import op
+from sqlalchemy import inspect
+
+# revision identifiers, used by Alembic.
+revision = '2d932114930d'
+down_revision = '8e71f2a4c9b0'
+branch_labels = None
+depends_on = None
+
+
+def _index_exists(table_name: str, index_name: str) -> bool:
+    bind = op.get_bind()
+    insp = inspect(bind)
+    return any(idx["name"] == index_name for idx in insp.get_indexes(table_name))
+
+
+def _create_index_if_not_exists(index_name: str, table_name: str, columns: list[str]) -> None:
+    if not _index_exists(table_name, index_name):
+        op.create_index(op.f(index_name), table_name, columns, unique=False)
+
+
+def _drop_index_if_exists(index_name: str, table_name: str) -> None:
+    if _index_exists(table_name, index_name):
+        op.drop_index(op.f(index_name), table_name=table_name)
+
+
+# (index_name, table_name, columns)
+_INDEXES = [
+    # api_keys.user_id (CASCADE -> users.id)
+    ('ix_api_keys_user_id', 'api_keys', ['user_id']),
+    # usage: wallet_id, provider_endpoint_id, provider_api_key_id (SET NULL)
+    ('ix_usage_wallet_id', 'usage', ['wallet_id']),
+    ('ix_usage_provider_endpoint_id', 'usage', ['provider_endpoint_id']),
+    ('ix_usage_provider_api_key_id', 'usage', ['provider_api_key_id']),
+    # wallet_transactions.operator_id (SET NULL -> users.id)
+    ('ix_wallet_transactions_operator_id', 'wallet_transactions', ['operator_id']),
+    # payment_callbacks.payment_order_id (SET NULL -> payment_orders.id)
+    ('ix_payment_callbacks_payment_order_id', 'payment_callbacks', ['payment_order_id']),
+    # refund_requests: payment_order_id, requested_by, approved_by, processed_by (SET NULL)
+    ('ix_refund_requests_payment_order_id', 'refund_requests', ['payment_order_id']),
+    ('ix_refund_requests_requested_by', 'refund_requests', ['requested_by']),
+    ('ix_refund_requests_approved_by', 'refund_requests', ['approved_by']),
+    ('ix_refund_requests_processed_by', 'refund_requests', ['processed_by']),
+    # proxy_nodes.registered_by (SET NULL -> users.id)
+    ('ix_proxy_nodes_registered_by', 'proxy_nodes', ['registered_by']),
+    # video_tasks: api_key_id, provider_id, endpoint_id, key_id, remixed_from_task_id
+    ('ix_video_tasks_api_key_id', 'video_tasks', ['api_key_id']),
+    ('ix_video_tasks_provider_id', 'video_tasks', ['provider_id']),
+    ('ix_video_tasks_endpoint_id', 'video_tasks', ['endpoint_id']),
+    ('ix_video_tasks_key_id', 'video_tasks', ['key_id']),
+    ('ix_video_tasks_remixed_from_task_id', 'video_tasks', ['remixed_from_task_id']),
+    # user_preferences.default_provider_id (-> providers.id)
+    ('ix_user_preferences_default_provider_id', 'user_preferences', ['default_provider_id']),
+    # announcements.author_id (SET NULL -> users.id)
+    ('ix_announcements_author_id', 'announcements', ['author_id']),
+    # announcement_reads.announcement_id (-> announcements.id)
+    ('ix_announcement_reads_announcement_id', 'announcement_reads', ['announcement_id']),
+    # request_candidates: user_id, api_key_id, endpoint_id, key_id (CASCADE)
+    ('ix_request_candidates_user_id', 'request_candidates', ['user_id']),
+    ('ix_request_candidates_api_key_id', 'request_candidates', ['api_key_id']),
+    ('ix_request_candidates_endpoint_id', 'request_candidates', ['endpoint_id']),
+    ('ix_request_candidates_key_id', 'request_candidates', ['key_id']),
+]
+
+
+def upgrade() -> None:
+    for index_name, table_name, columns in _INDEXES:
+        _create_index_if_not_exists(index_name, table_name, columns)
+
+
+def downgrade() -> None:
+    for index_name, table_name, _columns in reversed(_INDEXES):
+        _drop_index_if_exists(index_name, table_name)