fix: don't start the fetch-service in managed mode (#542)

Fixes #537

craft_application/services/fetch.py

@@ -90,7 +90,7 @@ def setup(self) -> None:
                 "and still in development."
             )
 
-        self._fetch_process = fetch.start_service()
+            self._fetch_process = fetch.start_service()
 
     def create_session(self, instance: craft_providers.Executor) -> dict[str, str]:
         """Create a new session.

docs/reference/changelog.rst

@@ -12,6 +12,8 @@ Application
 
 - ``AppCommand`` subclasses now will always receive a valid ``app_config``
   dict.
+- Fixes a bug where the fetch-service integration would try to spawn the
+  fetch-service process when running in managed mode.
 
 Commands
 ========

tests/unit/services/test_fetch.py

@@ -186,3 +186,13 @@ def test_warning_experimental(mocker, fetch_service, run_on_host, emitter):
     warning_emitted = call("message", warning) in emitter.interactions
 
     assert warning_emitted == run_on_host
+
+
+def test_setup_managed(mocker, fetch_service):
+    """The fetch-service process should only be checked/started when running on the host."""
+    mock_start = mocker.patch.object(fetch, "start_service")
+    mocker.patch.object(ProviderService, "is_managed", return_value=True)
+
+    fetch_service.setup()
+
+    assert not mock_start.called