feat(desktop): add screen recording (task 0029)

Add a wf-recorder module, enabled by the desktop aggregator. Super+Shift+R
picks a region with slurp and toggles a video-only capture (no audio), stopped
with SIGINT so the file finalises, saved to ~/Videos/Recordings. Start and
saved notifications fire via notify-send.

A Waybar custom/recording widget samples the wf-recorder process once a second
and shows a video glyph while a capture runs.

.claude/tasks/0029-screen-recording.md

@@ -13,8 +13,28 @@ No audio capture and no full-screen recording variant.
 
 ## Acceptance criteria
 
-- [ ] A wf-recorder module exists in the desktop group and is enabled by the aggregator.
+- [x] A wf-recorder module exists in the desktop group and is enabled by the aggregator.
-- [ ] The recorder selects a region first, then toggles video-only recording on `Super+Shift+R`.
+- [x] The recorder selects a region first, then toggles video-only recording on `Super+Shift+R`.
-- [ ] A recording indicator appears in the bar, and notifications fire on start and stop.
+- [x] A recording indicator appears in the bar, and notifications fire on start and stop.
-- [ ] No audio is captured and no full-screen variant is provided.
+- [x] No audio is captured and no full-screen variant is provided.
-- [ ] neogaia builds green under `nix flake check`.
+- [x] neogaia builds green under `nix flake check`.
+
+## Implementation Notes
+
+- **Toggle design.**
+  One key both starts and stops.
+  A running capture is stopped with SIGINT so wf-recorder finalises the file; otherwise slurp picks a region and wf-recorder runs in the foreground for the whole recording, so the same invocation fires the "saved" notification once the file is written.
+  Region-first and video-only (no `-a`, so no audio) satisfy the spec directly, and no full-screen variant is offered.
+
+- **Bar indicator polls rather than signals.**
+  The Waybar `custom/recording` widget samples the wf-recorder process with `pgrep` on a one-second interval, showing a video glyph while a capture runs and collapsing to nothing when idle.
+  An earlier draft signalled Waybar (`pkill -RTMIN+9`) from the toggle, but the start path raised the signal before wf-recorder had launched, so `pgrep` saw nothing and the indicator never lit during a recording — caught in review.
+  Polling is race-free, removes the signal number shared across two files, and is adequate for a status glyph.
+
+- **No waybar `window-rewrite` icon.**
+  wf-recorder is headless and slurp is a transient selection overlay, so neither owns a workspace window and the per-application icon convention does not apply.
+
+- **Recordings land in `~/Videos/Recordings`**, timestamped `recording-<date>.mp4`, with the directory created on first capture.
+
+- **Live capture is the irreducible manual step.**
+  The build is green, the config parses under `Hyprland --verify-config`, and the indicator's idle/recording transitions are verified against a stand-in process; exercising a real slurp selection and wf-recorder capture needs a running session.

modules/desktop/desktop.nix

@@ -15,6 +15,7 @@ in
     modules.desktop.hypridle.enable = lib.mkDefault true;
     modules.desktop.login.enable = lib.mkDefault true;
     modules.desktop.mako.enable = lib.mkDefault true;
+    modules.desktop.recording.enable = lib.mkDefault true;
     modules.desktop.rofi.enable = lib.mkDefault true;
     modules.desktop.screenshot.enable = lib.mkDefault true;
     modules.desktop.terminal.enable = lib.mkDefault true;

modules/desktop/recording.nix

@@ -0,0 +1,54 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+# Keybound screen recording: pick a region, then toggle a video-only capture.
+let
+  cfg = config.modules.desktop.recording;
+  user = config.user.name;
+
+  slurp = "${pkgs.slurp}/bin/slurp";
+  wf-recorder = "${pkgs.wf-recorder}/bin/wf-recorder";
+  notify-send = "${pkgs.libnotify}/bin/notify-send";
+  pgrep = "${pkgs.procps}/bin/pgrep";
+  pkill = "${pkgs.procps}/bin/pkill";
+  date = "${pkgs.coreutils}/bin/date";
+  mkdir = "${pkgs.coreutils}/bin/mkdir";
+
+  recDir = "$HOME/Videos/Recordings";
+
+  # A single key both starts and stops.
+  # A running wf-recorder is stopped with SIGINT so it finalises the file.
+  # Otherwise slurp picks a region and wf-recorder runs in the foreground until
+  # that stop arrives, so this instance lives for the whole recording and then
+  # reports it saved.
+  # No -a means no audio is captured.
+  toggle = pkgs.writeShellScript "screen-record-toggle" ''
+    if ${pgrep} -x wf-recorder >/dev/null; then
+      ${pkill} -INT -x wf-recorder
+      exit 0
+    fi
+
+    region=$(${slurp}) || exit 0
+    ${mkdir} -p "${recDir}"
+    file="${recDir}/recording-$(${date} +%Y%m%d-%H%M%S).mp4"
+
+    ${notify-send} -a "Screen recording" "Recording started" "Region capture, no audio."
+    ${wf-recorder} -g "$region" -f "$file"
+    ${notify-send} -a "Screen recording" "Recording saved" "$file"
+  '';
+in
+{
+  options.modules.desktop.recording.enable = lib.mkEnableOption "wf-recorder screen recording";
+
+  config = lib.mkIf cfg.enable {
+    home-manager.users.${user} = {
+      # $mod is defined by the compositor config these binds share.
+      wayland.windowManager.hyprland.settings.bind = [
+        "$mod SHIFT, R, exec, ${toggle}"
+      ];
+    };
+  };
+}

modules/desktop/waybar.nix

@@ -28,6 +28,16 @@ let
     ${pkgs.mako}/bin/makoctl mode -t dnd >/dev/null 2>&1
     ${pkgs.procps}/bin/pkill -RTMIN+8 waybar
   '';
+
+  # Lit while a wf-recorder capture is running.
+  # Empty text collapses the widget when idle, so it shows nothing until then.
+  recStatus = pkgs.writeShellScript "waybar-recording-status" ''
+    if ${pkgs.procps}/bin/pgrep -x wf-recorder >/dev/null; then
+      printf '{"text":"${g "f03d"}","tooltip":"Recording","class":"recording"}\n'
+    else
+      printf '{"text":"","class":"idle"}\n'
+    fi
+  '';
 in
 {
   options.modules.desktop.waybar.enable = lib.mkEnableOption "the Waybar status bar";
@@ -52,6 +62,7 @@ in
         modules-left = [ "hyprland/workspaces" ];
         modules-center = [ "clock" ];
         modules-right = [
+          "custom/recording"
           "mpris"
           "wireplumber"
           "network"
@@ -134,6 +145,14 @@ in
           interval = "once";
           signal = 8;
         };
+
+        # Recording state has no event to hook, so the widget samples the
+        # wf-recorder process once a second.
+        "custom/recording" = {
+          return-type = "json";
+          exec = "${recStatus}";
+          interval = 1;
+        };
       };
     };
   };