상위 디렉터리 및 카테고리의 소유권을 검증하지 않던 문제 등 버그 수정 및 Vitest 기반 테스트 추가

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/service-worker/modules/metadata.ts

@@ -0,0 +1,46 @@
+import { self } from "$app/service-worker";
+import { fileMetadataStore } from "../stores";
+import type { FileMetadata, ServiceWorkerResponse } from "../types";
+
+const METADATA_REQUEST_TIMEOUT_MS = 3000;
+
+const requestFromClient = (client: Client, fileId: number) => {
+  return new Promise<FileMetadata | null>((resolve) => {
+    const channel = new MessageChannel();
+    const timeout = setTimeout(() => {
+      channel.port1.close();
+      resolve(null);
+    }, METADATA_REQUEST_TIMEOUT_MS);
+
+    channel.port1.onmessage = (event: MessageEvent<FileMetadata | null>) => {
+      clearTimeout(timeout);
+      channel.port1.close();
+      resolve(event.data);
+    };
+    client.postMessage(
+      { type: "decryption-metadata-request", fileId } satisfies ServiceWorkerResponse,
+      [channel.port2],
+    );
+  });
+};
+
+export const getFileMetadata = async (fileId: number, clientId: string) => {
+  const cached = fileMetadataStore.get(fileId);
+  if (cached) return cached;
+
+  // The worker might have been restarted since the client prepared the decryption
+  const requestingClient = clientId ? await self.clients.get(clientId) : undefined;
+  const windowClients = await self.clients.matchAll({ type: "window" });
+  const candidates = [
+    ...(requestingClient ? [requestingClient] : []),
+    ...windowClients.filter(({ id }) => id !== requestingClient?.id),
+  ];
+
+  for (const client of candidates) {
+    const metadata = await requestFromClient(client, fileId);
+    if (metadata) {
+      fileMetadataStore.set(fileId, metadata);
+      return metadata;
+    }
+  }
+};