feat(quickshell): privacy indicator at the head of the rail

A lit icon tops the rail while another program records from a
microphone, uses a camera, or shares the screen. It is read from
PipeWire: capture streams for the mic, links out of video sources for
the camera and screencasts. The tooltip names the recording apps.

quickshell/README.md

@@ -43,7 +43,9 @@ cost 4.4% of the height on top of what the bar already takes.
   `Super+S` scratchpad holds windows, filled while it is open); the focused window, the
   player, the CPU/MEM/GPU readout and the clock on the right.
 - **rail** — network, bluetooth, audio, mic, backlight, battery, tray,
-  notifications, power. Popouts grow leftward out of it, into the screen.
+  notifications, power. While something records the mic, uses a camera or
+  shares the screen, a lit icon heads the rail (`services/Privacy.qml`, read
+  from PipeWire). Popouts grow leftward out of it, into the screen.
 
 Modules are divided by hairlines. `BarPill` is chromeless by default — a module
 is *content inside* the hull, not a surface of its own — and marks hover with

quickshell/bar/Rail.qml

@@ -47,6 +47,19 @@ PanelWindow {
         anchors.horizontalCenter: parent.horizontalCenter
         spacing: 0
 
+        // Something is recording or watching. First on the rail and in the
+        // light, because it is the one thing here you did not ask to see.
+        RailIcon {
+            id: privacyIcon
+            visible: Privacy.active
+            icon: Privacy.screen ? "󰹑" : (Privacy.camera ? "󰄀" : "󰍬")
+            label: "In use"
+            statusText: Privacy.detail
+            live: true
+        }
+
+        Divider { visible: Privacy.active }
+
         RailIcon {
             id: netIcon
             icon: Net.icon

quickshell/services/Privacy.qml

@@ -0,0 +1,58 @@
+pragma Singleton
+
+import QtQuick
+import Quickshell
+import Quickshell.Services.Pipewire
+
+// Whether anything is listening or watching: an app recording from a
+// microphone, a camera in use, or the screen being shared. All three show up
+// in PipeWire, so this needs no polling — a capture stream exists only while
+// something records, and a video source has links only while something
+// consumes it.
+Singleton {
+    id: root
+
+    // Capture streams from other programs. The shell's own level meters are
+    // capture streams too, and do not count.
+    readonly property var micUsers: Pipewire.nodes.values.filter(n =>
+        n.properties?.["media.class"] === "Stream/Input/Audio"
+        && !root._isShell(n))
+
+    readonly property var videoLinks: Pipewire.links.values.filter(l =>
+        String(l.source?.properties?.["media.class"] ?? "").startsWith("Video/"))
+
+    // xdg-desktop-portal-hyprland names its screencast nodes "xdph-…".
+    readonly property bool screen: root.videoLinks.some(l => root._isScreencast(l.source))
+    readonly property bool camera: root.videoLinks.some(l => !root._isScreencast(l.source))
+    readonly property bool mic: root.micUsers.length > 0
+    readonly property bool active: root.mic || root.camera || root.screen
+
+    // Who is doing it, for the tooltip.
+    readonly property string detail: {
+        const parts = [];
+        if (root.screen) parts.push("Screen shared");
+        if (root.camera) parts.push("Camera on");
+        if (root.mic) {
+            const apps = [...new Set(root.micUsers.map(n =>
+                n.properties?.["application.name"] || n.name || "an app"))];
+            parts.push("Mic: " + apps.join(", "));
+        }
+        return parts.join(" · ");
+    }
+
+    function _isShell(n): bool {
+        const who = (String(n.properties?.["application.process.binary"] ?? "") + " "
+            + String(n.properties?.["application.name"] ?? "")).toLowerCase();
+        return who.includes("quickshell") || /(^|\s)qs(\s|$)/.test(who);
+    }
+
+    function _isScreencast(n): bool {
+        const name = String(n?.name ?? n?.properties?.["node.name"] ?? "");
+        return name.startsWith("xdph");
+    }
+
+    // Node properties fill in only once a node is bound.
+    PwObjectTracker {
+        objects: Pipewire.nodes.values.filter(n => n.isStream || !n.isSink)
+    }
+}