Carry the vocabulary hint as prompt from the engines through the worker into every window

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

tests/protocol.test.ts

@@ -35,6 +35,7 @@ describe("isUiToWorkerMessage", () => {
       { type: "transcribe", audio: new Float32Array(8), requestId: "live-3" },
       { type: "transcribe", audio: new Float32Array(8), requestId: "engine-1-1", stream: true },
       { type: "transcribe", audio: new Float32Array(8), stream: false },
+      { type: "transcribe", audio: new Float32Array(8), prompt: "Maxwell, Voices of the Void" },
     ];
     for (const message of [...loads, ...transcribes]) {
       expect(isUiToWorkerMessage(message)).toBe(true);
@@ -65,6 +66,9 @@ describe("isUiToWorkerMessage", () => {
     expect(
       isUiToWorkerMessage({ type: "transcribe", audio: new Float32Array(4), stream: "yes" }),
     ).toBe(false);
+    expect(
+      isUiToWorkerMessage({ type: "transcribe", audio: new Float32Array(4), prompt: 5 }),
+    ).toBe(false);
     expect(isUiToWorkerMessage({ type: "result", text: "", chunks: [] })).toBe(false);
   });
 });