Fix: Merge background tasks from dependency and custom response

fastapi/routing.py

@@ -396,6 +396,27 @@ def get_request_handler(
             if isinstance(raw_response, Response):
                 if raw_response.background is None:
                     raw_response.background = solved_result.background_tasks
+                elif solved_result.background_tasks:
+                    from starlette.background import BackgroundTask, BackgroundTasks
+
+                    # Create a new BackgroundTasks to hold both
+                    combined_tasks = BackgroundTasks()
+                    
+                    # Add existing response tasks
+                    if isinstance(raw_response.background, BackgroundTasks):
+                        combined_tasks.tasks.extend(raw_response.background.tasks)
+                    elif isinstance(raw_response.background, BackgroundTask):
+                        combined_tasks.tasks.append(raw_response.background)
+                    
+                    # Add dependency tasks
+                    # solved_result.background_tasks is always BackgroundTasks (from dependencies/utils.py)
+                    if isinstance(solved_result.background_tasks, BackgroundTasks):
+                        combined_tasks.tasks.extend(solved_result.background_tasks.tasks)
+                    elif isinstance(solved_result.background_tasks, BackgroundTask):
+                         # Should not happen for BackgroundTasks dependency but safe to handle
+                        combined_tasks.tasks.append(solved_result.background_tasks)
+                        
+                    raw_response.background = combined_tasks
                 response = raw_response
             else:
                 response_args: Dict[str, Any] = {

tests/test_issue_11215.py

@@ -0,0 +1,21 @@
+from fastapi import BackgroundTasks, FastAPI
+from fastapi.testclient import TestClient
+from starlette.responses import BackgroundTask, Response
+
+app = FastAPI()
+
+@app.get("/")
+def endpoint(tasks: BackgroundTasks):
+    tasks.add_task(lambda: print("Dependency task executed"))
+    return Response(
+        content="Custom response",
+        background=BackgroundTask(lambda: print("Response task executed")),
+    )
+
+client = TestClient(app)
+
+def test_issue_11215(capsys):
+    client.get("/")
+    captured = capsys.readouterr()
+    assert "Dependency task executed" in captured.out
+    assert "Response task executed" in captured.out