Fix stale state in user turn stop strategies between turns

Reset stop strategies at turn start (not just turn stop) so that late
transcriptions arriving between turns do not leave stale _text that
causes premature stops on the next turn. Also cancel pending timeout
tasks in reset() for both SpeechTimeout and TurnAnalyzer strategies.

tests/test_user_turn_stop_strategy.py

@@ -493,6 +493,50 @@ class TestSpeechTimeoutUserTurnStopStrategy(unittest.IsolatedAsyncioTestCase):
         # Finalized transcript received after timeout, triggers immediately
         self.assertTrue(should_start)
 
+    async def test_reset_clears_stale_text_no_premature_stop(self):
+        """Test that reset() clears stale text and cancels timeout, preventing premature stop.
+
+        Reproduces the bug from issue #4053: after turn 1 completes and
+        reset() is called, a late transcription sets _text. If reset() is
+        called again at turn 2 start, the stale _text should be cleared
+        so no premature stop occurs on VAD stop.
+        """
+        strategy = await self._create_strategy()
+
+        stop_count = 0
+
+        @strategy.event_handler("on_user_turn_stopped")
+        async def on_user_turn_stopped(strategy, params):
+            nonlocal stop_count
+            stop_count += 1
+
+        # === Turn 1: S-T-E ===
+        await strategy.process_frame(VADUserStartedSpeakingFrame())
+        await strategy.process_frame(TranscriptionFrame(text="Hello!", user_id="cat", timestamp=""))
+        await strategy.process_frame(VADUserStoppedSpeakingFrame())
+        await asyncio.sleep(AGGREGATION_TIMEOUT + 0.1)
+        self.assertEqual(stop_count, 1)
+
+        # Reset after turn 1 (as controller would do at turn stop)
+        await strategy.reset()
+
+        # === Late transcription arrives between turns ===
+        await strategy.process_frame(TranscriptionFrame(text="Hello!", user_id="cat", timestamp=""))
+
+        # Reset at turn 2 start (the fix: controller now resets stop strategies at turn start)
+        await strategy.reset()
+
+        # === Turn 2: S-T-E (transcription arrives during turn) ===
+        await strategy.process_frame(VADUserStartedSpeakingFrame())
+        await strategy.process_frame(
+            TranscriptionFrame(text="How are you?", user_id="cat", timestamp="")
+        )
+        await strategy.process_frame(VADUserStoppedSpeakingFrame())
+
+        # Wait for timeout — should get turn 2 stop with the real transcription
+        await asyncio.sleep(AGGREGATION_TIMEOUT + 0.1)
+        self.assertEqual(stop_count, 2)
+
 
 class TestExternalUserTurnStopStrategy(unittest.IsolatedAsyncioTestCase):
     async def test_external_strategy(self):