refactor(vr): route headset audio with a WirePlumber hook

A default-node hook selects wivrn.sink/wivrn.source whenever they exist,
so the polling wivrn-audio.nu unit, its saved state and `just vr-audio`
go away. Streams follow via linking.follow-default-target.

Assisted-by: Claude Code (claude-opus-5-5)

Justfile

@@ -366,26 +366,16 @@ game:
 del-failed:
   kubectl delete pod --all-namespaces --field-selector="status.phase==Failed"
 
-# Start PC VR on idols-ai and route desktop audio to the headset.
+# Start PC VR on idols-ai; WirePlumber routes audio to the headset once it connects.
 [linux]
 [group('vr')]
 vr:
   systemctl --user start wivrn.service
-  systemctl --user stop wivrn-audio.service | complete | ignore
-  systemd-run --user --collect --unit=wivrn-audio nu {{absolute_path("scripts/wivrn-audio.nu")}} switch --timeout 600
 
-# Route audio to a headset that is connected right now.
+# Stop PC VR when finished.
-[linux]
-[group('vr')]
-vr-audio:
-  nu {{absolute_path("scripts/wivrn-audio.nu")}} switch --timeout 60
-
-# Stop PC VR when finished and restore the previous audio devices.
 [linux]
 [group('vr')]
 vr-stop:
-  systemctl --user stop wivrn-audio.service | complete | ignore
-  nu {{absolute_path("scripts/wivrn-audio.nu")}} restore
   systemctl --user stop wivrn.service
 
 # Show PC VR service status.

hosts/idols-ai/VR.md

@@ -42,11 +42,7 @@ configurations blindly.
    just vr-status
    ```
 
-   `just vr` returns immediately and leaves `wivrn-audio.service` waiting up to ten minutes for the
+   `just vr-stop` stops it again. Starting the service does not enable it for future logins.
-   headset. When it connects, that unit makes WiVRn's speaker and microphone the defaults and moves
-   any stream that is already playing. `just vr-audio` does the same switch in the foreground when
-   the headset is already connected, and `just vr-stop` cancels the wait and restores the saved
-   devices. Starting the service does not enable it for future logins.
 
 4. Allow a new headset to pair for two minutes:
 
@@ -59,8 +55,9 @@ configurations blindly.
    command again.
 
 5. Audio follows the headset: WiVRn's `wivrn.sink` and `wivrn.source` exist only while a headset is
-   connected, so the switch happens then, not at `just vr` time. Check the current defaults with
+   connected, and a WirePlumber hook in [`ai/vr.nix`](./ai/vr.nix) makes them the defaults for
-   `pactl get-default-sink` and `pactl get-default-source`.
+   exactly that time; playing streams follow. Your own default devices stay saved and return when
+   the headset disconnects. Check with `pactl get-default-sink` and `pactl get-default-source`.
 
 Manage paired headsets with `wivrnctl list-paired`, `wivrnctl rename`, or `wivrnctl unpair`. Consult
 `wivrnctl --help` and the subcommand's `--help` for arguments.

hosts/idols-ai/ai/vr.nix

@@ -30,6 +30,42 @@
     steam.importOXRRuntimes = true;
   };
 
+  # Make the headset's speaker and microphone the defaults while it is connected.
+  services.pipewire.wireplumber = {
+    extraScripts."wivrn-default.lua" = ''
+      local wanted = { ["audio.sink"] = "wivrn.sink", ["audio.source"] = "wivrn.source" }
+
+      SimpleEventHook {
+        name = "custom/wivrn-default",
+        after = { "default-nodes/find-best-default-node" },
+        before = { "default-nodes/apply-default-node" },
+        interests = {
+          EventInterest { Constraint { "event.type", "=", "select-default-node" } },
+        },
+        execute = function (event)
+          local name = wanted [event:get_properties () ["default-node.type"]]
+          local nodes = event:get_data ("available-nodes")
+          for _, props in ipairs (nodes and nodes:parse () or {}) do
+            if props ["node.name"] == name then
+              event:set_data ("selected-node", name)
+              return
+            end
+          end
+        end
+      }:register ()
+    '';
+    extraConfig.wivrn-default = {
+      "wireplumber.components" = [
+        {
+          name = "wivrn-default.lua";
+          type = "script/lua";
+          provides = "custom.wivrn-default";
+        }
+      ];
+      "wireplumber.profiles".main."custom.wivrn-default" = "required";
+    };
+  };
+
   # Wait for the control interface used by wivrnctl before reporting success.
   systemd.user.services.wivrn.serviceConfig = {
     Type = "dbus";

scripts/wivrn-audio.nu

@@ -1,142 +0,0 @@
-#!/usr/bin/env nu
-#
-# Route desktop audio to the WiVRn headset, and back again.
-#
-# WiVRn creates its speaker (wivrn.sink) and microphone (wivrn.source) only
-# while a headset is connected, so this script waits (bounded) for those nodes
-# before it switches the default devices and moves the streams that are already
-# playing. The previous defaults are saved under $XDG_RUNTIME_DIR, so they last
-# for the login session only; WirePlumber's persisted defaults stay untouched.
-#
-#   just vr        start the service, then route audio to the headset
-#   just vr-audio  route audio after a headset connected later
-#   just vr-stop   restore the previous devices, then stop the service
-#
-# See hosts/idols-ai/VR.md.
-
-# WiVRn's PipeWire node names (server/driver/wivrn_session.cpp).
-const SINK = "wivrn.sink"
-const SOURCE = "wivrn.source"
-
-# 'pactl list' output for a target ("sinks", "sources", "sink-inputs", ...).
-def list-devices [target: string] {
-  (^pactl --format=json list $target | complete | get stdout | from json)
-}
-
-# The device called $name, or null.
-def find-device [target: string, name: string] {
-  let matches = (list-devices $target | where name == $name)
-  if ($matches | is-empty) { null } else { $matches | get 0 }
-}
-
-# Wait for $name to appear, up to $seconds; returns null on timeout.
-def wait-for-device [target: string, name: string, seconds: int] {
-  let deadline = (date now) + ($seconds * 1sec)
-  mut waited = 0
-  loop {
-    let device = (find-device $target $name)
-    if $device != null { return $device }
-    if (date now) > $deadline { return null }
-    sleep 2sec
-    $waited += 2
-    if ($waited mod 30) == 0 { print $"audio: still waiting for the headset (($waited)s)" }
-  }
-}
-
-# Where the previous defaults are remembered (per login session).
-def state-path [] {
-  let runtime = ($env.XDG_RUNTIME_DIR? | default $"/run/user/(^id -u | str trim)")
-  $runtime | path join "wivrn-audio.json"
-}
-
-# The current default sink or source name.
-def default-device [kind: string] {
-  (^pactl $"get-default-($kind)" | complete | get stdout | str trim)
-}
-
-# Point the default sink or source at $name.
-def set-default-device [kind: string, name: string] {
-  ^pactl $"set-default-($kind)" $name | complete | ignore
-}
-
-# Move every playback stream to $sink.
-def move-sink-inputs [sink: string] {
-  for input in (list-devices "sink-inputs") {
-    ^pactl move-sink-input ($input.index | into string) $sink | complete | ignore
-  }
-}
-
-# Move every recording stream to $source.
-def move-source-outputs [source: string] {
-  for output in (list-devices "source-outputs") {
-    ^pactl move-source-output ($output.index | into string) $source | complete | ignore
-  }
-}
-
-# Point the default devices at the headset and follow with current streams.
-def switch [seconds: int] {
-  print $"audio: waiting up to ($seconds)s for the headset to connect"
-  let sink = (wait-for-device "sinks" $SINK $seconds)
-  if $sink == null {
-    print $"audio: the headset did not connect within ($seconds)s; run 'just vr-audio' once it does"
-    return
-  }
-
-  let state = (state-path)
-  if (default-device "sink") != $SINK {
-    { sink: (default-device "sink"), source: (default-device "source") } | to json | save -f $state
-  }
-
-  set-default-device "sink" $SINK
-  move-sink-inputs $SINK
-  print $"audio: playback -> ($SINK), previous default saved in ($state)"
-
-  let source = (find-device "sources" $SOURCE)
-  if $source != null {
-    set-default-device "source" $SOURCE
-    move-source-outputs $SOURCE
-    print $"audio: microphone -> ($SOURCE)"
-  } else {
-    print $"audio: no ($SOURCE) yet, microphone left alone"
-  }
-}
-
-# Put the remembered default devices back.
-def restore [] {
-  let state = (state-path)
-  if not ($state | path exists) {
-    print "audio: no saved defaults, nothing to restore"
-    return
-  }
-
-  let previous = (open --raw $state | from json)
-  rm $state
-
-  if (find-device "sinks" $previous.sink) == null {
-    print $"audio: ($previous.sink) is gone, leaving the default to WirePlumber"
-  } else {
-    set-default-device "sink" $previous.sink
-    move-sink-inputs $previous.sink
-    print $"audio: playback -> ($previous.sink)"
-  }
-
-  if (find-device "sources" $previous.source) == null {
-    print $"audio: ($previous.source) is gone, leaving the default to WirePlumber"
-  } else {
-    set-default-device "source" $previous.source
-    move-source-outputs $previous.source
-    print $"audio: microphone -> ($previous.source)"
-  }
-}
-
-# Entry point: 'nu wivrn-audio.nu switch' / '... restore'.
-def main [
-  action: string = "switch" # switch to the headset, or restore the previous devices
-  --timeout: int = 120 # seconds to wait for the headset audio devices
-] {
-  match $action {
-    "switch" => { switch $timeout }
-    "restore" => { restore }
-    _ => { error make { msg: $"unknown action '($action)'; expected switch or restore" } }
-  }
-}