Add TTS volume, a browser preview, and the split-audio plan

poc/src/audio-service.ts

@@ -156,7 +156,7 @@ export class AudioService {
      * grows. The wrapper touches `<file>.ready` after the first word, which is the reliable
      * signal; a size threshold and a timeout cover providers that do not mark readiness.
      */
-    private async playWhenReady(file: string): Promise<void> {
+    private async playWhenReady(file: string, volume?: number): Promise<void> {
         for (let attempt = 0; attempt < 400; attempt++) {
             try {
                 if (statSync(`${file}.ready`).size >= 0) break;
@@ -172,7 +172,7 @@ export class AudioService {
         }
 
         try {
-            await this.manager.play(file);
+            await this.manager.play(file, volume);
         } finally {
             try {
                 unlinkSync(`${file}.ready`);
@@ -182,6 +182,23 @@ export class AudioService {
         }
     }
 
+    /** The TTS output directory, for serving preview files. */
+    get ttsDirectory(): string {
+        return this.tts.directory;
+    }
+
+    /**
+     * Synthesize a line for browser playback. This never touches the call:
+     * no queue, no ducking, no virtual microphone, no voice-processing bypass.
+     */
+    async preview(text: string, options: TtsOptions = {}): Promise<string> {
+        const trimmed = text.trim();
+        if (!trimmed) throw new Error("text is required");
+        if (trimmed.length > 1000) throw new Error("text is too long (max 1000 characters)");
+
+        return this.tts.synthesize(trimmed, { ...options, stream: false, onOutputPath: undefined });
+    }
+
     stop(): void {
         this.queue.length = 0;
         this.manager.stopPlayback();
@@ -402,7 +419,7 @@ export class AudioService {
                 options.onOutputPath = path => {
                     streaming = (async () => {
                         await this.applyDuck(this.shouldDuck());
-                        await this.playWhenReady(path);
+                        await this.playWhenReady(path, item.options.volume);
                     })();
                 };
             }
@@ -413,7 +430,7 @@ export class AudioService {
                 await pending;
             } else {
                 await this.applyDuck(this.shouldDuck());
-                await this.manager.play(file);
+                await this.manager.play(file, item.options.volume);
             }
         } catch (error) {
             console.error("[audio] speak failed:", (error as Error).message);