restructure and test, pure python and rust transport both _work_

cht/stream/manager.py

@@ -168,10 +168,11 @@ class StreamManager:
         return self.recorder.alive() if self.recorder else True  # Rust owns it
 
     def start_scene_detector(self, on_new_frames=None):
-        if self.recorder:
-            self.recorder.set_on_new_scene_frames(on_new_frames)
-        else:
-            self.processor.set_on_new_frames(on_new_frames)
+        # GUI callback always goes to the processor — it fires on_new_frames
+        # after writing the JPEG to disk, regardless of how it got the frame.
+        self.processor.set_on_new_frames(on_new_frames)
+        if not self.recorder:
+            # Rust transport: processor connects to scene.sock and runs its own ffmpeg.
             self.processor.start_scene_detector(threshold=SCENE_THRESHOLD)
 
     def capture_now(self, on_new_frames=None):

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