Add cancel + progress UI, EngineToggle, and Docker deployment

src/lib/engine.ts

@@ -42,9 +42,16 @@ export interface EngineTranscribeOptions {
    * Browser engine: token fragments; server engine: whole segments.
    */
   onPartial?: (fragment: string) => void;
+  /**
+   * How far the pass has progressed through the audio. Browser engine only —
+   * faster-whisper's stream carries no window boundaries, so the server
+   * engine never calls it (the UI degrades to segments-as-feedback).
+   */
+  onProgress?: (progress: { processedSeconds: number; totalSeconds: number }) => void;
   /**
    * Abort the run. Honored by the server engine (the request is cancelled
-   * server-side too); the browser worker cannot abort a pass yet (M6).
+   * server-side too); the browser worker cannot abort a pass — cancel there
+   * is worker termination via `BrowserEngine.failAll` (D-018).
    */
   signal?: AbortSignal;
 }
@@ -83,6 +90,7 @@ interface PendingRequest {
   resolve: (result: EngineTranscribeResult) => void;
   reject: (error: Error) => void;
   onPartial?: (fragment: string) => void;
+  onProgress?: (progress: { processedSeconds: number; totalSeconds: number }) => void;
 }
 
 /**
@@ -116,11 +124,19 @@ export class BrowserEngine implements Engine {
   ): Promise<EngineTranscribeResult> {
     const requestId = `engine-${this.instance}-${++this.nextRequestId}`;
     return new Promise((resolve, reject) => {
-      this.pending.set(requestId, { resolve, reject, onPartial: options.onPartial });
+      this.pending.set(requestId, {
+        resolve,
+        reject,
+        onPartial: options.onPartial,
+        onProgress: options.onProgress,
+      });
       const message: TranscribeMessage = {
         type: "transcribe",
         audio,
         requestId,
+        // Id-carrying requests default to no streaming in the worker (the
+        // live-pass rule) — ask for it explicitly when a consumer listens.
+        ...((options.onPartial || options.onProgress) && { stream: true }),
         ...(options.language !== undefined &&
           options.language !== "auto" && { language: options.language }),
         ...(options.task !== undefined && { task: options.task }),
@@ -146,6 +162,12 @@ export class BrowserEngine implements Engine {
       case "partial":
         request.onPartial?.(data.text);
         break;
+      case "transcribe-progress":
+        request.onProgress?.({
+          processedSeconds: data.processedSeconds,
+          totalSeconds: data.totalSeconds,
+        });
+        break;
       case "result":
         this.pending.delete(data.requestId);
         request.resolve({ text: data.text, chunks: data.chunks });