Fix speaker-track readiness race: skip mixed-file wait when tracks exist

bot.py

@@ -287,7 +287,16 @@ async def process_recording(
             )
             return
 
-        if not await wait_for_file_ready(file_path):
+        # Speaker tracks are written and finalized independently in MeetingSink
+        # cleanup — they always have valid WAV headers if they exist.  Check
+        # them first so we can skip the mixed-file "ready" wait (which is prone
+        # to timing races with the SilenceGenerator shutdown path).
+        if _load_speaker_tracks(file_path):
+            logger.info(
+                "Speaker tracks present for guild_id=%s; skipping mixed-file readiness check",
+                guild_id,
+            )
+        elif not await wait_for_file_ready(file_path):
             reason = "recording file was not finalized in time"
             await _save_retry_state(guild_id, file_path, fallback_channel_id, reason)
             await safe_send_chunked(