feat(scenario): let context.downloadFile save data: URLs as run artifacts

Scenario steps can now persist in-script generated content (e.g. an
obtained VC's JWT) as a run file via context.downloadFile('data:...'),
without needing a network fetch. Bumps to 1.8.0.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

server/src/common/file-downloader.ts

@@ -5,6 +5,18 @@ import { URL } from "url";
 const MAX_FILE_SIZE = 100 * 1024 * 1024; // 100 MB
 const TIMEOUT_MS = 30000; // 30 seconds
 
+function decodeDataUrl(urlStr: string): Buffer {
+  const match = /^data:([^,]*),(.*)$/s.exec(urlStr);
+  if (!match) {
+    throw new Error("Malformed data: URL");
+  }
+  const [, meta, data] = match;
+  if (meta.endsWith(";base64")) {
+    return Buffer.from(data, "base64");
+  }
+  return Buffer.from(decodeURIComponent(data), "utf-8");
+}
+
 export async function downloadFile(
   urlStr: string,
   options?: {
@@ -13,6 +25,10 @@ export async function downloadFile(
     body?: string;
   },
 ): Promise<Buffer> {
+  if (urlStr.startsWith("data:")) {
+    return decodeDataUrl(urlStr);
+  }
+
   const url = new URL(urlStr);
   const protocol = url.protocol === "https:" ? https : http;
   const method = options?.method ?? "GET";