service_runner: Fix starting a service twice

pkgs/clan-cli/clan_lib/service_runner/container_test.py

@@ -301,14 +301,12 @@ def test_start_service_twice_transient(service_manager: ServiceManagerProtocol)
     status = service_manager.get_status("simple-service")
     assert status == "running"
 
-    # Try to start the same service again - this should fail
-    # systemd won't allow starting a unit with the same name
-    with pytest.raises(ClanError, match="Failed to start service"):
-        service_manager.start_service(
-            name="simple-service",
-            command=["sleep", "300"],
-            autostart=False,
-        )
+    # Try to start the same service again - this shouldn't fail
+    service_manager.start_service(
+        name="simple-service",
+        command=["sleep", "300"],
+        autostart=False,
+    )
 
     # Original service should still be running
     status = service_manager.get_status("simple-service")

pkgs/clan-cli/clan_lib/service_runner/systemd_user.py

@@ -184,6 +184,13 @@ class SystemdUserService:
         service_name = self._service_name(name)
         self._check_executable(command)
 
+        # Stop and reset any existing service (allows redefining failed/running services)
+        self._systemctl("stop", service_name)
+        run(
+            ["systemctl", "--user", "reset-failed", f"{service_name}.service"],
+            RunOpts(check=False),
+        )
+
         if autostart:
             if group:
                 self._create_target_file(group)
@@ -223,10 +230,7 @@ class SystemdUserService:
 
             cmd.extend(command)
 
-            result = run(cmd, RunOpts(check=False))
-            if result.returncode != 0:
-                msg = f"Failed to start service: {result.stderr}"
-                raise ClanError(msg)
+            result = run(cmd, RunOpts(error_msg="Failed to start service"))
 
         return name