Refactor WASM module loading and validation logic

src/lib/wasmLoader.ts

@@ -1,5 +1,6 @@
 import type { StoreSnapshot } from '../state/types';
 import { buildRustSimBridge, type RustSimBridge, type WasmSimExports } from './wasmSimBridge';
+import type { InitOutput } from '../gen/rust_engine';
 import { normalizeSnapshot, validateSnapshotForWasm } from '../state/serialization/store';
 import { parityDebugEnabled } from './parityDebug';
 
@@ -27,25 +28,44 @@
 
   try {
     // Dynamic import to allow tree-shaking when WASM is not used
-    const wasmModule = await import('../gen/rust_engine');
-    const initOutput = await wasmModule.default();
-    const memory = (initOutput as { memory?: WebAssembly.Memory }).memory;
-    if (!memory) {
-      throw new Error('WASM init missing memory');
-    }
+      const mod = (await import('../gen/rust_engine')) as unknown;
 
-    if (
-      parityDebugEnabled &&
-      typeof (wasmModule as { set_parity_debug?: (enabled: boolean) => void }).set_parity_debug ===
-        'function'
-    ) {
-      (wasmModule as { set_parity_debug?: (enabled: boolean) => void }).set_parity_debug?.(true);
-    }
+      type RustEngineModule = WasmSimExports & {
+        default: (...args: unknown[]) => Promise<InitOutput>;
+        set_parity_debug?: (enabled: boolean) => void;
+      };
 
-    const exports: WasmSimExports = {
-      memory,
-      WasmGameState: wasmModule.WasmGameState,
-    };
+      const isRustEngineModule = (m: unknown): m is RustEngineModule => {
+        if (typeof m !== 'object' || m === null) return false;
+        const r = m as Record<string, unknown>;
+        return (
+          typeof r.default === 'function' &&
+          typeof r.WasmGameState === 'function' &&
+          // `memory` is returned from the init output rather than being a top-level export
+          true
+        );
+      };
+
+      if (!isRustEngineModule(mod)) {
+        throw new Error('Imported rust_engine module has an unexpected shape');
+      }
+
+      const wasmModule = mod;
+      const initOutput = await wasmModule.default();
+      const memory = initOutput.memory;
+      const hasMemoryBuffer = Boolean(memory && (memory as { buffer?: unknown }).buffer);
+      if (!hasMemoryBuffer && !(memory instanceof WebAssembly.Memory)) {
+        throw new Error('WASM init missing memory');
+      }
+
+      if (parityDebugEnabled && typeof wasmModule.set_parity_debug === 'function') {
+        wasmModule.set_parity_debug(true);
+      }
+
+      const exports: WasmSimExports = {
+        memory,
+        WasmGameState: wasmModule.WasmGameState,
+      };
 
     // Pre-validate the original snapshot and provide friendly messages
     // if it looks incomplete. We still normalize and proceed because