feat(db): download_task 增加缺席记录与代数字段（迁移 0067）

missing_since / missing_count 记录 qB 里连续查不到的起点与轮数；generation 记录 removed 行复活次数，用于完成事件幂等键换代。contracts DownloadTask 同步为可选字段。

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Cxwgnn2pbzQ7rXv3rq7fei

packages/db/migrations/0067_download_missing.ts

@@ -0,0 +1,25 @@
+import type { Kysely } from "kysely";
+import { execDdl } from "../src/migration-helpers.ts";
+
+// 下载调度卡死修复(docs/plan/system-review.md ③):
+// - missing_since / missing_count:qB 列表与按 hash 查都查不到时先记缺席,连续多轮才判 removed,中途出现即清零
+// - generation:同一 (实例, hash) 的 removed 行被再次提交 / 接管而复活时 +1,完成事件幂等键随之换代,
+//   复活后的完成仍能触发整理
+// biome-ignore lint/suspicious/noExplicitAny: 迁移不依赖应用表类型
+export async function up(db: Kysely<any>): Promise<void> {
+  await execDdl(
+    db,
+    `alter table download_task add column if not exists missing_since timestamptz;
+     alter table download_task add column if not exists missing_count integer not null default 0;
+     alter table download_task add column if not exists generation integer not null default 0;`,
+  );
+}
+// biome-ignore lint/suspicious/noExplicitAny: 同上
+export async function down(db: Kysely<any>): Promise<void> {
+  await execDdl(
+    db,
+    `alter table download_task drop column if exists missing_since;
+     alter table download_task drop column if exists missing_count;
+     alter table download_task drop column if exists generation;`,
+  );
+}

packages/db/src/types.ts

@@ -719,6 +719,9 @@ export interface DownloadTaskTable {
   updated_at: GeneratedTimestamptz;
   media_entity_id: string | null;
   import_plan_id: string | null;
+  missing_since: Timestamptz | null;
+  missing_count: Generated<number>;
+  generation: Generated<number>;
 }
 
 export interface DownloaderInstanceTable {