fix: close data integrity and hot-reload review findings

Backfill same-day snapshots for newly added or restored videos, preserve successful fan snapshots on resume, persist incomplete state before forced re-runs, and split collection completion from backup completion so failed backups can retry without API calls. Reject missing data payloads instead of treating them as empty folders, guard against mass-unfav on suspicious empty remote folders, rebuild Bilibili clients when credentials change, recompute primary folder ownership from active relations with per-folder fav_time, preserve original titles for dropped invalid videos, poll config every 60 seconds, and fix favsort verify interval and mixed resource types.

reaction_board/bilibili/provider.py

@@ -0,0 +1,38 @@
+# -*- coding: utf-8 -*-
+"""按账号角色提供 B 站客户端，并在凭据变化时自动重建。"""
+
+from __future__ import annotations
+
+from typing import Any, Callable
+
+from ..config import ConfigStore
+from .client import BilibiliClient
+
+
+class ClientProvider:
+    """缓存客户端；仅当 ``mid`` / ``cookie`` / ``csrf`` 变化时重建。
+
+    ``factory`` 负责固化该角色的限速与重试策略，因此重建不会丢失这些设置。
+    """
+
+    def __init__(
+        self,
+        store: ConfigStore,
+        role: str,
+        factory: Callable[[Any], BilibiliClient],
+    ) -> None:
+        if role not in {"read", "write"}:
+            raise ValueError(f"未知账号角色: {role}")
+        self.store = store
+        self.role = role
+        self.factory = factory
+        self._key: tuple[int, str, str] | None = None
+        self._client: BilibiliClient | None = None
+
+    def get(self) -> BilibiliClient:
+        credentials = getattr(self.store.get().bilibili, self.role)
+        key = (credentials.mid, credentials.cookie, credentials.csrf)
+        if self._client is None or key != self._key:
+            self._client = self.factory(credentials)
+            self._key = key
+        return self._client