Fix backend worker pipeline stall on exception (add fallback fallback)

inference.py

@@ -1138,10 +1138,14 @@ def run_inference(
                     flush_batch()
             except Exception as e:
                 logging.exception("Worker failed processing frame")
-                # Important: If we lose a batch, the pipeline might stall waiting for those indices.
-                # Ideally we should emit error placeholders?
-                # For now, just ensure we don't hold the lock.
-                raise
+                # Emit empty/failed frames for the batch to keep sequence alive
+                for idx, frm in batch_accum:
+                    try:
+                        # Fallback: Return original frame with empty detections
+                        queue_out.put((idx, frm, []), timeout=5.0)
+                    except:
+                        pass
+                batch_accum.clear()
             finally:
                 queue_in.task_done()
 
@@ -1473,13 +1477,15 @@ def run_segmentation(
 
             except Exception as e:
                 logging.error("Batch seg failed: %s", e)
+                # Fallback: Emit failed frames to prevent writer stall
                 for idx, frm in batch_accum:
                      while True:
                         try:
-                            queue_out.put((idx, frm), timeout=1.0) # Fallback
+                            # Return original frame without mask
+                            queue_out.put((idx, frm), timeout=1.0)
                             break
                         except Full:
-                             if writer_finished: raise
+                             if writer_finished: break
                              if job_id: _check_cancellation(job_id)
             batch_accum.clear()
 
@@ -1807,13 +1813,14 @@ def run_depth_inference(
 
             except Exception as e:
                 logging.error("Batch depth failed: %s", e)
+                # Fallback: Emit original frames (no depth map)
                 for idx, frm in batch_accum:
                      while True:
                         try:
                             queue_out.put((idx, frm), timeout=1.0)
                             break
                         except Full:
-                             if writer_finished: raise
+                             if writer_finished: break
                              if job_id: _check_cancellation(job_id)
             batch_accum.clear()