fix: reset init promise on failure to allow retry

If wasmInit() fails (e.g. WASM load error), clear the cached promise
so subsequent calls can retry instead of permanently returning the
rejected promise.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: yasumorishima

src/core/generate/rs.ts

@@ -9,7 +9,13 @@ let initPromise: Promise<void> | undefined;
 
 export async function wasmInit(...args: Parameters<typeof init>) {
   if (!initPromise) {
-    initPromise = init(...args).then(() => {});
+    initPromise = init(...args).then(
+      () => {},
+      (error: unknown) => {
+        initPromise = undefined;
+        throw error;
+      },
+    );
   }
   return initPromise;
 }