feat(cgroups): reassign apps from cgroups of a known launchers

Some launcher applications are visible in the i3/sway IPC and receive
transient unit of their own. All the apps started from these were left
in the launcher transient unit and any overrides targeted to these apps
did not apply.

src/assign-cgroups.py

@@ -39,6 +39,12 @@
 LOG = logging.getLogger("assign-cgroups")
 SD_BUS_NAME = "org.freedesktop.systemd1"
 SD_OBJECT_PATH = "/org/freedesktop/systemd1"
+SD_SLICE_FORMAT = "app-{app_id}.slice"
+SD_UNIT_FORMAT = "app-{app_id}-{unique}.scope"
+# Ids of known launcher applications that are not special surfaces. When the app is
+# started using one of those, it should be moved to a new cgroup.
+# Launcher should only be listed here if it creates cgroup of its own.
+LAUNCHER_APPS = ["nwggrid"]
 
 
 def get_cgroup(pid: int) -> Optional[str]:
@@ -173,7 +179,11 @@ def get_pid(self, con: Con) -> Optional[int]:
 
     def cgroup_change_needed(self, cgroup: Optional[str]) -> bool:
         """Check criteria for assigning current app into an isolated cgroup"""
-        # TODO: check for known launchers
+        if cgroup is None:
+            return False
+        for launcher in LAUNCHER_APPS:
+            if SD_SLICE_FORMAT.format(app_id=launcher) in cgroup:
+                return True
         return cgroup == self._compositor_cgroup
 
     @retry(
@@ -187,8 +197,8 @@ async def assign_scope(self, app_id: str, proc: Process):
         app-{app_id}.slice/app{app_id}-{pid}.scope cgroup
         """
         app_id = escape_app_id(app_id)
-        sd_unit = f"app-{app_id}-{proc.pid}.scope"
-        sd_slice = f"app-{app_id}.slice"
+        sd_slice = SD_SLICE_FORMAT.format(app_id=app_id)
+        sd_unit = SD_UNIT_FORMAT.format(app_id=app_id, unique=proc.pid)
         # Collect child processes as systemd assigns a scope only to explicitly
         # specified PIDs.
         # There's a risk of race as the child processes may exit by the time dbus call