Fix Piper memory pressure on iOS

tests/piper-onnx-config.test.cjs

@@ -14,10 +14,19 @@ test('ONNX Runtime base URL rejects an invalid worker origin', async () => {
   assert.throws(() => createOnnxWasmPaths('undefined'), TypeError);
 });
 
-test('ONNX Runtime uses one thread and a bounded startup timeout', async () => {
+test('Piper and ONNX Runtime stay on one thread even though Piper overwrites ONNX settings', async () => {
   const {configureOnnxRuntime} = await import('../piper-onnx-config.mjs');
+  const navigatorObject = {hardwareConcurrency: 8};
+  const previousNavigator = globalThis.navigator;
+  Object.defineProperty(globalThis, 'navigator', {configurable: true, value: navigatorObject});
   const runtime = {env: {wasm: {numThreads: 0, initTimeout: 0}}};
-  configureOnnxRuntime(runtime);
-  assert.equal(runtime.env.wasm.numThreads, 1);
-  assert.equal(runtime.env.wasm.initTimeout, 60000);
+  try {
+    configureOnnxRuntime(runtime);
+    assert.equal(navigatorObject.hardwareConcurrency, 1);
+    assert.equal(runtime.env.wasm.numThreads, 1);
+    assert.equal(runtime.env.wasm.initTimeout, 60000);
+  } finally {
+    if (previousNavigator === undefined) delete globalThis.navigator;
+    else Object.defineProperty(globalThis, 'navigator', {configurable: true, value: previousNavigator});
+  }
 });

tests/piper-worker-format.test.cjs

@@ -11,3 +11,9 @@ test('Piper worker is built and started as an ES module', async () => {
   assert.match(buildScript, /outfile: join\(workerRoot, 'piper-worker\.js'\),\s*bundle: true,\s*format: 'esm'/);
   assert.match(runtime, /new Worker\(workerUrl, \{type: 'module'\}\)/);
 });
+
+test('Piper runtime discards a worker after a failed initialization for a clean retry', async () => {
+  const runtime = await readFile(join(__dirname, '..', 'piper-runtime.js'), 'utf8');
+  assert.match(runtime, /TtsSession keeps a singleton even when ONNX initialization fails/);
+  assert.match(runtime, /worker\?\.terminate\(\);\s*worker = null;/);
+});