fix: sync partial transcripts to chat when turn ends

Previously, chat messages were lost when only STTPartialTranscriptEvent
events were received and no final STTTranscriptEvent arrived before the
turn ended. The transcript was sent to the LLM but never synced to chat.

This fix moves chat sync from the STTTranscriptEvent handler to
_on_turn_event, ensuring the accumulated transcript (from partials or
finals) is always recorded in chat when a turn completes.

Author: d3xvn

agents-core/vision_agents/core/agents/agents.py

@@ -339,25 +339,9 @@ async def on_stt_transcript_event_create_response(
         async def on_error(event: STTErrorEvent):
             self.logger.error("stt error event %s", event)
 
-        @self.events.subscribe
-        async def on_stt_transcript_event_sync_conversation(event: STTTranscriptEvent):
-            if self.conversation is None:
-                return
-
-            user_id = event.user_id()
-            if user_id is None:
-                raise ValueError("missing user_id")
-
-            with self.span("agent.on_stt_transcript_event_sync_conversation"):
-                await self.conversation.upsert_message(
-                    message_id=str(uuid.uuid4()),
-                    role="user",
-                    user_id=user_id,
-                    content=event.text or "",
-                    completed=True,
-                    replace=True,  # Replace any partial transcripts
-                    original=event,
-                )
+        # Note: STTTranscriptEvent chat sync is handled in _on_turn_event to ensure
+        # partial transcripts are also synced when no final transcript arrives.
+        # See _sync_user_transcript_to_chat() for the implementation.
 
         @self.events.subscribe
         async def on_realtime_user_speech_transcription(
@@ -461,6 +445,27 @@ async def simple_audio_response(
         if _is_audio_llm(self.llm):
             await self.llm.simple_audio_response(pcm, participant)
 
+    async def _sync_user_transcript_to_chat(
+        self, transcript: str, user_id: str
+    ) -> None:
+        """Sync user transcript to chat conversation.
+
+        Called when a turn ends to ensure the user's message is recorded in chat,
+        whether it came from final STTTranscriptEvent or only partial transcripts.
+        """
+        if self.conversation is None or not transcript:
+            return
+
+        with self.span("agent._sync_user_transcript_to_chat"):
+            await self.conversation.upsert_message(
+                message_id=str(uuid.uuid4()),
+                role="user",
+                user_id=user_id,
+                content=transcript,
+                completed=True,
+                replace=True,
+            )
+
     def subscribe(self, function):
         """Subscribe a callback to the agent-wide event bus.
 
@@ -1098,6 +1103,11 @@ async def _on_turn_event(self, event: TurnStartedEvent | TurnEndedEvent) -> None
                 buffer.reset()
 
             if transcript.strip():
+                # Sync user transcript to chat (handles both final and partial-only cases)
+                await self._sync_user_transcript_to_chat(
+                    transcript, event.participant.user_id
+                )
+
                 # cancel the old task if the text changed in the meantime
 
                 if (