fix(tts): keep final webchat audio supplemental

extensions/speech-core/src/tts.test.ts

@@ -156,6 +156,7 @@ async function expectTtsPayloadResult(params: {
     expect(synthesizeMock).toHaveBeenCalledWith(expect.objectContaining({ target: params.target }));
     expect(result.audioAsVoice).toBe(params.audioAsVoice);
     expect(result.mediaUrl).toMatch(new RegExp(`voice-\\d+\\.${params.mediaExtension ?? "ogg"}$`));
+    expect(result.spokenText).toBe(params.text);
 
     mediaDir = result.mediaUrl ? path.dirname(result.mediaUrl) : undefined;
   } finally {

extensions/speech-core/src/tts.ts

@@ -1591,6 +1591,7 @@ export async function maybeApplyTtsToPayload(params: {
       ...nextPayload,
       mediaUrl: result.audioPath,
       audioAsVoice: result.audioAsVoice || params.payload.audioAsVoice,
+      spokenText: textForAudio,
     };
   }