refactor(backend/api): remove duplicate cache control header and ensure consistent read for job updates

Author: cristofima

backend/README.md

@@ -267,9 +267,9 @@ Or mount `~/.aws` when using Docker (already configured in docker-compose.yml).
 
 The API implements strict caching controls to ensure UI consistency:
 
-- **GET /jobs/{id}**: `Cache-Control: private, max-age=0, must-revalidate`. Forces browsers to validate ETag on every request, ensuring deployment status changes are seen immediately.
+- **GET /jobs/{id}**: `Cache-Control: private, max-age=0, must-revalidate`. Forces browsers to validate ETag on every request, ensuring deployment status changes are seen immediately. Uses DynamoDB Strong Consistency (`ConsistentRead=True`) to generate accurate ETags.
 - **DELETE /jobs/{id}**: Returns `Cache-Control: no-store, no-cache, must-revalidate, max-age=0` to immediately invalidate client caches.
-- **Consistency**: Critical endpoints (`update_job_metadata`, `deploy_model`) use DynamoDB Strong Consistency (`ConsistentRead=True`) to guarantee read-after-write accuracy.
+- **Consistency**: Critical operations (`update_job_metadata`, `deploy_model`) use DynamoDB Strong Consistency (`ConsistentRead=True`) to guarantee read-after-write accuracy.
 
 ## 🧪 Testing
 
@@ -280,14 +280,14 @@ The backend includes comprehensive unit and integration tests for both API and T
 ```
 backend/tests/
 ├── pytest.ini              # Pytest configuration
-├── api/                    # API tests (104 tests, 69% coverage)
+├── api/                    # API tests (109 tests, 71% coverage)
 │   ├── conftest.py         # Shared fixtures
 │   ├── test_endpoints.py   # Endpoint tests (39 tests)
 │   ├── test_schemas.py     # Pydantic validation tests (23 tests)
 │   ├── test_dynamo_service.py   # DynamoDB service tests
 │   ├── test_s3_service.py       # S3 service tests
 │   └── test_services_integration.py  # moto-based integration tests (21 tests)
-└── training/               # Training tests (159 tests, 53% coverage)
+└── training/               # Training tests (159 tests, 63% coverage)
     ├── conftest.py         # Shared fixtures
     ├── unit/               # Pure unit tests
     │   ├── test_preprocessor.py

backend/api/routers/models.py

@@ -220,9 +220,6 @@ async def delete_job(job_id: str, response: Response, delete_data: bool = True)
         # Ensure client caches are invalidated immediately
         response.headers["Cache-Control"] = "no-store, no-cache, must-revalidate, max-age=0"
 
-        # Ensure client caches are invalidated immediately
-        response.headers["Cache-Control"] = "no-store, no-cache, must-revalidate, max-age=0"
-        
         return {
             "message": "Job deleted successfully",
             "job_id": job_id,
@@ -247,7 +244,8 @@ async def update_job_metadata(job_id: str, update_request: JobUpdateRequest, res
     """
     try:
         # Verify job exists
-        job = dynamodb_service.get_job(job_id)
+        # Use consistent read to ensure we have the absolute latest state before validating and updating
+        job = dynamodb_service.get_job(job_id, consistent_read=True)
         if not job:
             raise HTTPException(
                 status_code=status.HTTP_404_NOT_FOUND,

backend/api/services/s3_service.py

@@ -118,9 +118,6 @@ def generate_presigned_download_url_cached(
             logger.info(f"Cached presigned URL for s3://{bucket}/{key} (TTL: {cache_ttl}s)")
             return url
 
-            logger.info(f"Cached presigned URL for s3://{bucket}/{key} (TTL: {cache_ttl}s)")
-            return url
-    
     def check_object_exists(self, bucket: str, key: str) -> bool:
         """Check if an object exists in S3"""
         try: