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>

src/lib/engine.ts

@@ -37,6 +37,11 @@ export interface EngineTranscribeOptions {
   language?: string;
   /** transcribe | translate (multilingual models only). */
   task?: WhisperTask;
+  /**
+   * "Names and terms" vocabulary hint, raw user text (D-WS2a). Applies to
+   * every Whisper model, `.en` ones included; empty/undefined = no prompt.
+   */
+  prompt?: string;
   /**
    * Streaming transcript fragments — append each to the text shown so far.
    * Browser engine: token fragments; server engine: whole segments.
@@ -140,6 +145,7 @@ export class BrowserEngine implements Engine {
         ...(options.language !== undefined &&
           options.language !== "auto" && { language: options.language }),
         ...(options.task !== undefined && { task: options.task }),
+        ...(options.prompt && { prompt: options.prompt }),
       };
       // Ownership of the audio moves to the worker — zero-copy transfer.
       this.worker.postMessage(message, [audio.buffer as ArrayBuffer]);
@@ -282,6 +288,8 @@ export class ServerEngine implements Engine {
       params.set("language", options.language);
     }
     if (options.task !== undefined) params.set("task", options.task);
+    // Validated + normalized server-side (parseLanguageAndTask, D-WS2a).
+    if (options.prompt) params.set("prompt", options.prompt);
 
     let response: Response;
     try {