revert: remove partial ASR (CPU thrashing hurt latency)

Partial ASR during speech ran multiple concurrent CPU-heavy
transcriptions, caused thread contention and slowed everything down.
Revert to single final ASR on VAD end.
Keep MIN_SILENCE_S at 0.4s.

asr_agent/conversation_worker.py

@@ -365,36 +365,9 @@ class Worker:
         vad = _SileroVAD()
         busy = False
         play_tasks: list[asyncio.Task] = []
-        partial_task: asyncio.Task | None = None
-
-        async def _partial_asr():
-            """Streaming partial ASR during speech (xiaozhi-style interim)."""
-            last_pos = 0
-            try:
-                while vad.in_speech:
-                    await asyncio.sleep(1.0)
-                    if busy or not vad.in_speech:
-                        continue
-                    total = len(buf.buffer)
-                    if total - last_pos < 4800:  # 0.3s new audio minimum
-                        continue
-                    audio = buf.buffer[last_pos:]
-                    if len(audio) < 4800:
-                        continue
-                    loop = asyncio.get_running_loop()
-                    result = await loop.run_in_executor(None, self.asr.transcribe_array, audio)
-                    txt = result.get("text", "").strip()
-                    if txt:
-                        logger.info("[%s] partial ASR: %s", sid, txt[:60])
-                        await self._send({"type": "partial", "text": txt, "seq": 0})
-                    last_pos = total
-            except asyncio.CancelledError:
-                pass
-            except Exception:
-                logger.exception("[%s] partial_asr failed", sid)
 
         async def _acc():
-            nonlocal busy, play_tasks, partial_task
+            nonlocal busy, play_tasks
             stream = rtc.AudioStream(track, sample_rate=sr, num_channels=1)
             fc = 0
             async for ev in stream:
@@ -407,12 +380,6 @@ class Worker:
                 was_speech = vad.in_speech
                 vad.process(arr)
 
-                # Start partial ASR when speech begins
-                if vad.in_speech and not was_speech:
-                    if partial_task and not partial_task.done():
-                        partial_task.cancel()
-                    partial_task = asyncio.create_task(_partial_asr())
-
                 if fc % 100 == 0:
                     logger.info("[%s] af#%d e=%.4f vad=%s blen=%d",
                                 sid, fc, float(np.sqrt(np.mean(arr ** 2))),
@@ -420,8 +387,6 @@ class Worker:
 
                 if was_speech and vad.should_end() and vad.min_speech_met():
                     logger.info("[%s] VAD END blen=%d", sid, len(buf.buffer))
-                    if partial_task and not partial_task.done():
-                        partial_task.cancel()
                     for pt in play_tasks:
                         if not pt.done():
                             pt.cancel()
@@ -437,8 +402,6 @@ class Worker:
 
                 if vad.in_speech and vad.total_samples >= int(MAX_SPEECH_S * sr):
                     logger.info("[%s] VAD MAX blen=%d", sid, len(buf.buffer))
-                    if partial_task and not partial_task.done():
-                        partial_task.cancel()
                     for pt in play_tasks:
                         if not pt.done():
                             pt.cancel()