Keep Parakeet on WASM unless WebGPU is chosen explicitly, and never offer it on phones

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/protocol.test.ts

@@ -2,6 +2,7 @@ import { describe, test, expect } from "bun:test";
 import {
   applyLoadProgress,
   deviceAttempts,
+  parakeetDeviceAttempts,
   dtypeRequiresF16,
   initialLoadProgress,
   isUiToWorkerMessage,
@@ -224,6 +225,29 @@ describe("deviceAttempts (D-004, D-017)", () => {
   });
 });
 
+describe("parakeetDeviceAttempts (D-WS7a)", () => {
+  const everything = { webnn: true, webgpu: true, webgpuF16: true };
+
+  test("auto never picks an accelerator for Parakeet", () => {
+    expect(parakeetDeviceAttempts("auto", everything)).toEqual(["wasm"]);
+  });
+
+  test("explicit WebGPU is tried (then WASM) only with shader-f16", () => {
+    expect(parakeetDeviceAttempts("webgpu", everything)).toEqual(["webgpu", "wasm"]);
+    expect(parakeetDeviceAttempts("webgpu", { ...everything, webgpuF16: false })).toEqual([
+      "wasm",
+    ]);
+    expect(parakeetDeviceAttempts("webgpu", { ...everything, webgpu: false })).toEqual([
+      "wasm",
+    ]);
+  });
+
+  test("WebNN and WASM preferences run WASM", () => {
+    expect(parakeetDeviceAttempts("webnn", everything)).toEqual(["wasm"]);
+    expect(parakeetDeviceAttempts("wasm", everything)).toEqual(["wasm"]);
+  });
+});
+
 describe("TranscribeProgressTracker", () => {
   // Production shape: 30 s windows advancing by 20 s (30 − 2·5, the worker's
   // chunk/stride settings), like the chunked ASR pipeline.