fix(cgroups): improve escaping of systemd unit names

WM_CLASS is loosely validated and can contain pretty much anything,
causing unit name validation failure on the systemd side. `app_id`
handler in sway can also be too permissive.
Escape everything that is not allowed in the systemd unit documentation.

Fixes #14

src/assign-cgroups.py

@@ -15,6 +15,7 @@
 import argparse
 import asyncio
 import logging
+import re
 import socket
 import struct
 from typing import Optional
@@ -46,10 +47,23 @@
 # Launcher should only be listed here if it creates cgroup of its own.
 LAUNCHER_APPS = ["nwgbar", "nwgdmenu", "nwggrid"]
 
+SD_UNIT_ESCAPE_RE = re.compile(r"[^\w:.\\]", re.ASCII)
+
 
 def escape_app_id(app_id: str) -> str:
-    """Escape app_id for systemd APIs"""
-    return app_id.replace("-", "\\x2d")
+    """Escape app_id for systemd APIs.
+
+    The "unit prefix" must consist of one or more valid characters (ASCII letters,
+    digits, ":", "-", "_", ".", and "\"). The total length of the unit name including
+    the suffix must not exceed 256 characters. [systemd.unit(5)]
+
+    We also want to escape "-" to avoid creating extra slices.
+    """
+
+    def repl(match):
+        return "".join([f"\\x{x:02x}" for x in match.group().encode()])
+
+    return SD_UNIT_ESCAPE_RE.sub(repl, app_id)
 
 
 LAUNCHER_APP_CGROUPS = [