fix(mobile): patch pyodide.js at runtime to bypass Chrome 61 import() syntax

Chrome 61 (Karoo WebView) cannot parse dynamic import() — a SyntaxError at
parse time prevents loadPyodide from ever being defined.

Fix: fetch pyodide.js as text, replace every import( with a __loadScript(
shim that uses <script> tag injection, then inject via Blob URL. The Blob
script is never pre-scanned for module syntax so the patch is invisible to
the parser.

Also: expose waitForEngine() from extractActivity so callers can await
engine readiness before batching files — manual scan now shows "Preparing
extraction engine…" instead of flooding with N individual failures.

mobile/extraction/extractActivity.ts

@@ -22,6 +22,24 @@ const pending = new Map<string, Pending>();
 let reqCounter = 0;
 let isExtracting = false;
 
+// Engine readiness — tracked so callers can wait before batching files.
+let _engineReady = false;
+let _engineError: string | null = null;
+const _engineResolvers: Array<() => void> = [];
+const _engineRejecters: Array<(e: Error) => void> = [];
+
+export function waitForEngine(timeoutMs = 300_000): Promise<void> {
+  if (_engineReady) return Promise.resolve();
+  if (_engineError) return Promise.reject(new Error(_engineError));
+  return new Promise((resolve, reject) => {
+    const timer = setTimeout(() => {
+      reject(new Error('Extraction engine timed out — check network and Bincio instance URL'));
+    }, timeoutMs);
+    _engineResolvers.push(() => { clearTimeout(timer); resolve(); });
+    _engineRejecters.push((e) => { clearTimeout(timer); reject(e); });
+  });
+}
+
 export function handleWebViewMessage(e: WebViewMessageEvent): void {
   let msg: Record<string, unknown>;
   try { msg = JSON.parse(e.nativeEvent.data); } catch { return; }
@@ -30,6 +48,14 @@ export function handleWebViewMessage(e: WebViewMessageEvent): void {
   const p = reqId ? pending.get(reqId) : undefined;
 
   switch (msg.type) {
+    case 'pyodide_ready':
+      _engineReady = true;
+      _engineResolvers.splice(0).forEach(fn => fn());
+      break;
+    case 'init_error':
+      _engineError = msg.message as string;
+      _engineRejecters.splice(0).forEach(fn => fn(new Error(_engineError!)));
+      break;
     case 'result':
       if (p) {
         pending.delete(reqId!);