Fix critical data flow and concurrency bugs

- Add empty padded_tracks guard in process_transcriptions
- Fix created_padded_files: use list instead of set to preserve order for zip cleanup
- Document size=0 contract in PadTrackResult (size=0 means original key, not padded)
- Remove redundant ctx.log in padding_workflow

server/reflector/hatchet/workflows/daily_multitrack_pipeline.py

@@ -429,7 +429,7 @@ async def process_paddings(input: PipelineInput, ctx: Context) -> ProcessPadding
     results = await padding_workflow.aio_run_many(bulk_runs)
 
     padded_tracks = []
-    created_padded_files = set()
+    created_padded_files = []
 
     for result in results:
         pad_result = PadTrackResult(**result[TaskName.PAD_TRACK])
@@ -445,7 +445,7 @@ async def process_paddings(input: PipelineInput, ctx: Context) -> ProcessPadding
 
         if pad_result.size > 0:
             storage_path = f"file_pipeline_hatchet/{input.transcript_id}/tracks/padded_{pad_result.track_index}.webm"
-            created_padded_files.add(storage_path)
+            created_padded_files.append(storage_path)
 
     ctx.log(f"process_paddings complete: {len(padded_tracks)} padded tracks")
 
@@ -476,6 +476,9 @@ async def process_transcriptions(
     target_language = participants_result.target_language
     padded_tracks = paddings_result.padded_tracks
 
+    if not padded_tracks:
+        raise ValueError("No padded tracks available for transcription")
+
     ctx.log(
         f"process_transcriptions: spawning {len(padded_tracks)} transcription workflows"
     )

server/reflector/hatchet/workflows/models.py

@@ -21,7 +21,11 @@ class ParticipantInfo(BaseModel):
 
 
 class PadTrackResult(BaseModel):
-    """Result from pad_track task."""
+    """Result from pad_track task.
+
+    If size=0, track required no padding and padded_key contains original S3 key.
+    If size>0, track was padded and padded_key contains new padded file S3 key.
+    """
 
     padded_key: NonEmptyString
     bucket_name: NonEmptyString | None

server/reflector/hatchet/workflows/padding_workflow.py

@@ -120,7 +120,6 @@ async def pad_track(input: PaddingInput, ctx: Context) -> PadTrackResult:
             finally:
                 Path(temp_path).unlink(missing_ok=True)
 
-        ctx.log(f"pad_track complete: track {input.track_index} -> {storage_path}")
         logger.info(
             "[Hatchet] pad_track complete",
             track_index=input.track_index,