restructure and test, pure python and rust transport both _work_

cht/stream/processor.py

@@ -496,10 +496,13 @@ class SessionProcessor:
                 log.info("Audio chunk: %s (%.1fs → %.1fs, global %.1fs)",
                          wav_path.name, processed_time, process_to, global_start)
                 if self._on_new_audio:
-                    self._on_new_audio(
-                        wav_path, global_start, chunk_duration,
-                        segment_path=source, local_start=processed_time,
-                    )
+                    try:
+                        self._on_new_audio(
+                            wav_path, global_start, chunk_duration,
+                            segment_path=source, local_start=processed_time,
+                        )
+                    except Exception as e:
+                        log.error("Audio callback failed: %s", e)
                 chunk_num += 1
 
             processed_time = process_to