feat: add task workflow and asset downloads

lib/server/storage.ts

@@ -181,19 +181,20 @@ export async function readLocalServedFile(area: "uploads" | "generated-results",
   }
 }
 
-export async function readLegacyPublicFile(pathParts: string[]): Promise<{
+export async function readAssetForDownload(asset: Asset): Promise<{
   bytes: Buffer;
   contentType: string;
 } | null> {
-  const filePath = join(process.cwd(), "runtime", "nianxx-play", "public", ...pathParts);
-  try {
-    return {
-      bytes: await readFile(filePath),
-      contentType: contentTypeForPath(filePath)
-    };
-  } catch {
-    return null;
-  }
+  const local = await readLocalAsset(asset);
+  if (local) return local;
+
+  if (!/^https?:\/\//i.test(asset.url)) return null;
+  const response = await fetch(asset.url);
+  if (!response.ok) return null;
+  return {
+    bytes: Buffer.from(await response.arrayBuffer()),
+    contentType: response.headers.get("content-type") || contentTypeForPath(new URL(asset.url).pathname)
+  };
 }
 
 export async function deleteStoredAsset(asset: Asset): Promise<void> {
@@ -218,6 +219,30 @@ export async function deleteStoredAsset(asset: Asset): Promise<void> {
   }
 }
 
+async function readLocalAsset(asset: Asset): Promise<{
+  bytes: Buffer;
+  contentType: string;
+} | null> {
+  const localPath = localServedPathParts(asset.storagePath) || localServedPathParts(asset.url);
+  if (!localPath) return null;
+  return readLocalServedFile(localPath.area, localPath.pathParts);
+}
+
+function localServedPathParts(value?: string): {
+  area: "uploads" | "generated-results";
+  pathParts: string[];
+} | null {
+  if (!value) return null;
+  const clean = value.replace(/^\/+/, "");
+  if (clean.startsWith("uploads/")) {
+    return { area: "uploads", pathParts: clean.slice("uploads/".length).split("/").filter(Boolean) };
+  }
+  if (clean.startsWith("generated-results/")) {
+    return { area: "generated-results", pathParts: clean.slice("generated-results/".length).split("/").filter(Boolean) };
+  }
+  return null;
+}
+
 async function storeBuffer(input: {
   bytes: Buffer;
   fileName: string;