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/worker/inference.worker.ts

@@ -17,6 +17,13 @@ import {
   type ProgressInfo,
 } from "@huggingface/transformers";
 import { resolveDefaultDtype } from "../lib/models";
+import {
+  buildPromptPrefix,
+  installPromptSupport,
+  PROMPT_PREFIX_KWARG,
+  type PromptableModel,
+  type PromptTokenizer,
+} from "./prompt";
 import {
   deviceAttempts,
   dtypeRequiresF16,
@@ -410,6 +417,17 @@ async function transcribe(message: TranscribeMessage): Promise<void> {
   if (message.task !== undefined) {
     options.task = message.task;
   }
+  // "Names and terms" hint (D-WS2a): one prefix per pass, applied by the
+  // generate() wrapper to every 30 s window (Transformers.js ignores
+  // `prompt_ids`, see src/worker/prompt.ts). The wrapper is idempotent.
+  const promptPrefix = buildPromptPrefix(
+    asr.tokenizer as unknown as PromptTokenizer,
+    message.prompt ?? "",
+  );
+  if (promptPrefix.length > 0) {
+    installPromptSupport(asr.model as unknown as PromptableModel);
+    options[PROMPT_PREFIX_KWARG] = promptPrefix;
+  }
 
   const output = await asr(message.audio, options);
 

src/worker/protocol.ts

@@ -87,6 +87,13 @@ export interface TranscribeMessage {
    * engine (which correlates via requestId, D-010) still streams.
    */
   stream?: boolean;
+  /**
+   * Optional "Names and terms" vocabulary hint, raw as the user typed it
+   * (D-WS2a). The worker normalizes it, truncates it to Whisper's prompt
+   * budget and feeds it as a decoder prompt to every window of this pass
+   * (src/worker/prompt.ts). Empty/omitted = no prompt.
+   */
+  prompt?: string;
 }
 
 export type UiToWorkerMessage = LoadMessage | TranscribeMessage;
@@ -318,7 +325,8 @@ export function isUiToWorkerMessage(value: unknown): value is UiToWorkerMessage
           value.task === "transcribe" ||
           value.task === "translate") &&
         isOptionalString(value.requestId) &&
-        (value.stream === undefined || typeof value.stream === "boolean")
+        (value.stream === undefined || typeof value.stream === "boolean") &&
+        isOptionalString(value.prompt)
       );
     default:
       return false;