Decky Loader not showing up on desktop

[TheSunCat]

Hi! I'd like to theme my desktop's Steam client, and I understand Decky Loader is able to inject CSS for this even outside of big picture mode. I added this repo to my flake, loaded the nixos module, and added jovian.decky-loader.enable = true. Upon launching steam I was logged out, so something definitely changed. However I do not see a Decky icon in Steam big picture (launched with -dev to enable CEF debugging). Am I missing something?

Logs from journalctl -o cat -u decky-loader:

Starting Steam Deck Plugin Loader...
Started Steam Deck Plugin Loader.
[helpers][WARNING]: Failed to execute get_system_pythonpaths(): [Errno 2] No such file or directory: 'python3'
[main][INFO]: Starting Decky version v3.0.5
[loader][INFO]: plugin_path: /var/lib/decky-loader/plugins
[loader][INFO]: import plugins from /var/lib/decky-loader/plugins
[main][INFO]: Loading Decky frontend!
[localplatformlinux][INFO]: Restarting steamwebhelper
[injector][WARNING]: The Tab SharedJSContext socket has been disconnected while listening for messages.
[main][INFO]: CEF has disconnected...
[base_events][ERROR]: Task exception was never retrieved
future: <Task finished name='Task-6' coro=<PluginManager.loader_reinjector() done, defined at /nix/store/wkad4i0kdy313mrnhadry08qzjrmkiph-python3.12-decky-loader-3.0.5/lib/python3.12/site-packages/decky_loader/main.py:175> exception=WSServerHandshakeError(RequestInfo(url=URL('ws://localhost:8080/devtools/page/A09641FBCEB8CF121A5DDF244CF11939'), method='GET', headers=<CIMultiDictProxy('Host': 'localhost:8080', 'Upgrade': 'websocket', 'Connection': 'Upgrade', 'Sec-WebSocket-Version': '13', 'Sec-WebSocket-Key': 'wJjXWeJU8+zeF0JVYg/HRA==', 'Accept': '*/*', 'Accept-Encoding': 'gzip, deflate, br', 'User-Agent': 'Python/3.12 aiohttp/3.11.11')>, real_url=URL('ws://localhost:8080/devtools/page/A09641FBCEB8CF121A5DDF244CF11939')), (), status=500, message='Invalid response status', headers=<CIMultiDictProxy('Content-Length': '51', 'Content-Type': 'text/html')>)>
Traceback (most recent call last):
  File "/nix/store/wkad4i0kdy313mrnhadry08qzjrmkiph-python3.12-decky-loader-3.0.5/lib/python3.12/site-packages/decky_loader/main.py", line 197, in loader_reinjector
    await tab.open_websocket()
  File "/nix/store/wkad4i0kdy313mrnhadry08qzjrmkiph-python3.12-decky-loader-3.0.5/lib/python3.12/site-packages/decky_loader/injector.py", line 36, in open_websocket
    self.websocket = await self.client.ws_connect(self.ws_url)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/c4v4aq01pjxw5cqc5brklvjbf0qw1w5i-python3.12-aiohttp-3.11.11/lib/python3.12/site-packages/aiohttp/client.py", line 1021, in _ws_connect
    raise WSServerHandshakeError(
aiohttp.client_exceptions.WSServerHandshakeError: 500, message='Invalid response status', url='ws://localhost:8080/devtools/page/A09641FBCEB8CF121A5DDF244CF11939'
[base_events][ERROR]: Unclosed client session
client_session: <aiohttp.client.ClientSession object at 0x7f62c0444740>
[base_events][ERROR]: Unclosed connector
connections: ['deque([(<aiohttp.client_proto.ResponseHandler object at 0x7f62c01d3d10>, 5731.025200018)])']
connector: <aiohttp.connector.TCPConnector object at 0x7f62c02e9520>
[loader][INFO]: Hot reload enabled
[updater][INFO]: Updated remote version information
[wsrouter][WARNING]: Dropping message as there is no connected socket: {'type': 3, 'event': 'loader/notify_updates', 'args': ()}