feat(downloads): 下载器单独的水位与保种天数

- contracts DownloaderPolicy(存 downloader_instance.settings.policy):硬阈值 / 恢复水位 / 清理目标 / 保种天数,
  不填用全局 cache / retention
- volumeThresholds:卷的生效水位 = 各实例「自己的值 ?? 全局」取最小;decideVolume、阈值清理、手动恢复、
  首页卷信息、定时清理检查都改用它;cleanupCandidates 保种天数按实例
- 保存时校验合并全局后 恢复 < 硬阈值、清理目标 ≤ 恢复
- 下载器设置表单新增四项(留空用全局)

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/web/app/components/settings/instances.tsx

@@ -90,6 +90,26 @@ export function DownloadersSection() {
   );
 }
 
+/** 下载器自己的水位 / 保种(settings.policy):表单里是字符串,空 = 用全局 */
+const POLICY_FIELDS = [
+  ["hardPct", "hardThresholdPercent"],
+  ["resumePct", "resumePercent"],
+  ["targetPct", "cleanupTargetPercent"],
+  ["seedDays", "seedRetentionDays"],
+] as const;
+function policyForm(r: DownloaderInstance): Record<string, string> {
+  const p = ((r.settings as { policy?: Record<string, unknown> }).policy ?? {}) as Record<string, unknown>;
+  return Object.fromEntries(POLICY_FIELDS.map(([f, k]) => [f, typeof p[k] === "number" ? String(p[k]) : ""]));
+}
+function policyBody(v: FormValues): Record<string, number> {
+  const out: Record<string, number> = {};
+  for (const [f, k] of POLICY_FIELDS) {
+    const raw = String(v[f] ?? "").trim();
+    if (raw !== "" && Number.isFinite(Number(raw))) out[k] = Number(raw);
+  }
+  return out;
+}
+
 function DownloadersTable() {
   const list = downloaders.useList();
   const create = downloaders.useCreate();
@@ -166,6 +186,22 @@ function DownloadersTable() {
           },
           { name: "managedTag", label: "管理标签", kind: "text", placeholder: "umt", hint: "只接管带此标签的任务" },
           { name: "cacheVolumeKey", label: "缓存卷标识", kind: "text", placeholder: "cache-1" },
+          {
+            name: "hardPct",
+            label: "硬阈值（%）",
+            kind: "number",
+            placeholder: "留空用全局",
+            hint: "这个下载器的缓存盘用到多少就停止新增下载；多个下载器共用一块盘时取最严格的",
+          },
+          { name: "resumePct", label: "恢复水位（%）", kind: "number", placeholder: "留空用全局" },
+          { name: "targetPct", label: "清理目标（%）", kind: "number", placeholder: "留空用全局" },
+          {
+            name: "seedDays",
+            label: "保种天数",
+            kind: "number",
+            placeholder: "留空用全局",
+            hint: "入库后至少保留几天再允许清理；公网 BT 可填 0（站点 H&R 要求仍然遵守）",
+          },
           {
             name: "isDefault",
             label: "设为默认下载器",
@@ -183,6 +219,10 @@ function DownloadersTable() {
           apiKey: "",
           managedTag: "umt",
           cacheVolumeKey: "",
+          hardPct: "",
+          resumePct: "",
+          targetPct: "",
+          seedDays: "",
           isDefault: false,
           enabled: true,
         },
@@ -197,6 +237,7 @@ function DownloadersTable() {
           "secret:authKind": authKindOf(r),
           managedTag: r.managedTag,
           cacheVolumeKey: r.cacheVolumeKey ?? "",
+          ...policyForm(r),
           isDefault: r.isDefault,
           enabled: r.enabled,
         }),
@@ -214,6 +255,7 @@ function DownloadersTable() {
                 : undefined,
           managedTag: optStr(v.managedTag),
           cacheVolumeKey: nullStr(v.cacheVolumeKey),
+          settings: { policy: policyBody(v) },
           isDefault: v.isDefault === true,
           enabled: v.enabled === true,
         }),