diff --git a/src/backend/common/database/cosmosdb.py b/src/backend/common/database/cosmosdb.py
index 46c020d0..8c56286a 100644
--- a/src/backend/common/database/cosmosdb.py
+++ b/src/backend/common/database/cosmosdb.py
@@ -94,19 +94,21 @@ async def create_batch(self, user_id: str, batch_id: UUID) -> BatchRecord:
                         batchexists = await self.batch_container.read_item(
                             item=str(batch_id), partition_key=str(batch_id)
                         )
-                        if batchexists.get("user_id") != user_id:
-                            self.logger.error("Batch belongs to a different user", batch_id=str(batch_id))
-                            raise CosmosResourceNotFoundError(message="Batch not found")
-                        self.logger.info("Returning existing batch record", batch_id=str(batch_id))
-                        return BatchRecord.fromdb(batchexists)
                     except CosmosResourceNotFoundError:
                         if attempt < 2:
                             self.logger.info("Batch read returned 404 after conflict, retrying", batch_id=str(batch_id), attempt=attempt + 1)
                             await asyncio.sleep(0.5 * (attempt + 1))
-                        else:
-                            raise RuntimeError(
-                                f"Batch {batch_id} already exists but could not be read after retries"
-                            )
+                            continue
+                        raise RuntimeError(
+                            f"Batch {batch_id} already exists but could not be read after retries"
+                        )
+
+                    if batchexists.get("user_id") != user_id:
+                        self.logger.error("Batch belongs to a different user", batch_id=str(batch_id))
+                        raise PermissionError("Batch not found")
+
+                    self.logger.info("Returning existing batch record", batch_id=str(batch_id))
+                    return BatchRecord.fromdb(batchexists)
 
         except Exception as e:
             self.logger.error("Failed to create batch", error=str(e))
diff --git a/src/backend/common/services/batch_service.py b/src/backend/common/services/batch_service.py
index 27a874e0..efce27fa 100644
--- a/src/backend/common/services/batch_service.py
+++ b/src/backend/common/services/batch_service.py
@@ -288,7 +288,7 @@ async def upload_file_to_batch(self, batch_id: str, user_id: str, file: UploadFi
             self.logger.info("File uploaded to blob storage", filename=file.filename, batch_id=batch_id)
 
             # Create file entry
-            file_record_obj = await self.database.add_file(batch_id, file_id, file.filename, blob_path)
+            file_record_obj = await self.database.add_file(UUID(batch_id), UUID(file_id), file.filename, blob_path)
             file_record_dict = getattr(file_record_obj, "dict", None)
             file_record = file_record_dict() if callable(file_record_dict) else file_record_obj
 
diff --git a/src/tests/backend/common/database/cosmosdb_test.py b/src/tests/backend/common/database/cosmosdb_test.py
index d08fb015..faaaaa09 100644
--- a/src/tests/backend/common/database/cosmosdb_test.py
+++ b/src/tests/backend/common/database/cosmosdb_test.py
@@ -11,7 +11,7 @@
 from uuid import uuid4  # noqa: E402
 
 from azure.cosmos.aio import CosmosClient  # noqa: E402
-from azure.cosmos.exceptions import CosmosResourceExistsError  # noqa: E402
+from azure.cosmos.exceptions import CosmosResourceExistsError, CosmosResourceNotFoundError  # noqa: E402
 
 from common.database.cosmosdb import (  # noqa: E402
     CosmosDBClient,
@@ -188,6 +188,84 @@ async def test_create_batch_exists(cosmos_db_client, mocker):
     )
 
 
+@pytest.mark.asyncio
+async def test_create_batch_conflict_retry_on_404(cosmos_db_client, mocker):
+    """Test that read_item is retried when it returns 404 after a 409 conflict."""
+    user_id = "user_1"
+    batch_id = uuid4()
+
+    mock_batch_container = mock.MagicMock()
+    mocker.patch.object(cosmos_db_client, 'batch_container', mock_batch_container)
+    mock_batch_container.create_item = AsyncMock(side_effect=CosmosResourceExistsError)
+
+    existing_batch = {
+        "id": str(batch_id),
+        "batch_id": str(batch_id),
+        "user_id": user_id,
+        "file_count": 0,
+        "created_at": datetime.now(timezone.utc).isoformat(),
+        "updated_at": datetime.now(timezone.utc).isoformat(),
+        "status": ProcessStatus.READY_TO_PROCESS,
+    }
+
+    # First call raises 404, second call succeeds
+    mock_batch_container.read_item = AsyncMock(
+        side_effect=[CosmosResourceNotFoundError(message="Not found"), existing_batch]
+    )
+
+    batch = await cosmos_db_client.create_batch(user_id, batch_id)
+
+    assert batch.batch_id == batch_id
+    assert batch.user_id == user_id
+    assert mock_batch_container.read_item.call_count == 2
+
+
+@pytest.mark.asyncio
+async def test_create_batch_conflict_cross_user(cosmos_db_client, mocker):
+    """Test that a PermissionError is raised when the batch belongs to a different user."""
+    user_id = "user_1"
+    batch_id = uuid4()
+
+    mock_batch_container = mock.MagicMock()
+    mocker.patch.object(cosmos_db_client, 'batch_container', mock_batch_container)
+    mock_batch_container.create_item = AsyncMock(side_effect=CosmosResourceExistsError)
+
+    existing_batch = {
+        "id": str(batch_id),
+        "batch_id": str(batch_id),
+        "user_id": "different_user",
+        "file_count": 0,
+        "created_at": datetime.now(timezone.utc).isoformat(),
+        "updated_at": datetime.now(timezone.utc).isoformat(),
+        "status": ProcessStatus.READY_TO_PROCESS,
+    }
+    mock_batch_container.read_item = AsyncMock(return_value=existing_batch)
+
+    with pytest.raises(PermissionError, match="Batch not found"):
+        await cosmos_db_client.create_batch(user_id, batch_id)
+
+
+@pytest.mark.asyncio
+async def test_create_batch_conflict_exhausted_retries(cosmos_db_client, mocker):
+    """Test that RuntimeError is raised when read_item returns 404 after all retries."""
+    user_id = "user_1"
+    batch_id = uuid4()
+
+    mock_batch_container = mock.MagicMock()
+    mocker.patch.object(cosmos_db_client, 'batch_container', mock_batch_container)
+    mock_batch_container.create_item = AsyncMock(side_effect=CosmosResourceExistsError)
+
+    # All 3 attempts raise 404
+    mock_batch_container.read_item = AsyncMock(
+        side_effect=CosmosResourceNotFoundError(message="Not found")
+    )
+
+    with pytest.raises(RuntimeError, match="already exists but could not be read after retries"):
+        await cosmos_db_client.create_batch(user_id, batch_id)
+
+    assert mock_batch_container.read_item.call_count == 3
+
+
 @pytest.mark.asyncio
 async def test_create_batch_exception(cosmos_db_client, mocker):
     user_id = "user_1"
@@ -487,6 +565,8 @@ async def mock_query_items(query, parameters, **kwargs):
     assert file["status"] == ProcessStatus.READY_TO_PROCESS
 
     mock_file_container.query_items.assert_called_once()
+    call_kwargs = mock_file_container.query_items.call_args
+    assert call_kwargs.kwargs.get("partition_key") == file_id
 
 
 @pytest.mark.asyncio
@@ -612,6 +692,8 @@ async def mock_query_items(query, parameters, **kwargs):
     assert batch["status"] == ProcessStatus.READY_TO_PROCESS
 
     mock_batch_container.query_items.assert_called_once()
+    call_kwargs = mock_batch_container.query_items.call_args
+    assert call_kwargs.kwargs.get("partition_key") == batch_id
 
 
 @pytest.mark.asyncio