refactor: simplify GCS job deletion to use prefix-based cleanup

Replace 3-stage redundant deletion with single prefix-based approach.
All job files are under {job_id}/ prefix, so listing and deleting by
prefix is simpler and catches all files including new types like
accessible_video.mp4 and ad_cues/*.mp3.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/api/v1/routes_jobs.py

@@ -1089,49 +1089,29 @@ async def delete_job(
 
 
 async def _delete_job_gcs_assets(job_id: str, job_doc: dict):
-    """Delete all GCS assets for a job"""
+    """Delete all GCS assets for a job using prefix-based cleanup.
+
+    All job files are stored under the {job_id}/ prefix in GCS, including:
+    - source.mp4 (original video)
+    - {lang}/captions.vtt (translated captions)
+    - {lang}/ad.vtt (audio description cues)
+    - {lang}/ad.mp3 (full AD audio)
+    - {lang}/ad_cues/cue_*.mp3 (per-cue TTS segments)
+    - {lang}/accessible_video.mp4 (rendered video)
+    - {lang}/accessible_captions.vtt (re-timed captions for pause-insert)
+    """
     try:
-        # Delete source file
-        source_gcs_uri = job_doc.get("source", {}).get("gcs_uri")
-        if source_gcs_uri:
-            blob_path = source_gcs_uri.replace(f"gs://{settings.gcs_bucket}/", "")
+        deleted_count = 0
+        blobs = gcs_service.bucket.list_blobs(prefix=f"{job_id}/")
+        for blob in blobs:
             try:
-                blob = gcs_service.bucket.blob(blob_path)
                 blob.delete()
-                logger.info(f"Deleted source file: {blob_path}")
+                deleted_count += 1
+                logger.debug(f"Deleted GCS file: {blob.name}")
             except Exception as e:
-                logger.warning(f"Could not delete source file {blob_path}: {e}")
-
-        # Delete output files
-        outputs = job_doc.get("outputs", {})
-        for lang, lang_outputs in outputs.items():
-            if not isinstance(lang_outputs, dict):
-                continue
-
-            # Delete VTT files
-            for key in ["captions_vtt_gcs", "ad_vtt_gcs", "ad_mp3_gcs"]:
-                if key in lang_outputs:
-                    gcs_uri = lang_outputs[key]
-                    blob_path = gcs_uri.replace(f"gs://{settings.gcs_bucket}/", "")
-                    try:
-                        blob = gcs_service.bucket.blob(blob_path)
-                        blob.delete()
-                        logger.info(f"Deleted output file: {blob_path}")
-                    except Exception as e:
-                        logger.warning(f"Could not delete output file {blob_path}: {e}")
-
-        # Delete entire job folder if it exists
-        try:
-            blobs = gcs_service.bucket.list_blobs(prefix=f"{job_id}/")
-            for blob in blobs:
-                try:
-                    blob.delete()
-                    logger.info(f"Deleted remaining file: {blob.name}")
-                except Exception as e:
-                    logger.warning(f"Could not delete {blob.name}: {e}")
-        except Exception as e:
-            logger.warning(f"Could not list/delete job folder {job_id}/: {e}")
+                logger.warning(f"Could not delete {blob.name}: {e}")
 
+        logger.info(f"Deleted {deleted_count} GCS files for job {job_id}")
     except Exception as e:
         logger.error(f"Error deleting GCS assets for job {job_id}: {e}")
         raise