Share a Wi-Fi network by QR code

GNOME's Wi-Fi panel has this and it is the most-used thing in it: the
alternative is reading a passphrase out loud. Network & Devices now shows
a scannable code for any saved network whose passphrase this user can
read.

The image contains the network password in machine-readable form, so
most of the care here is about that rather than about QR codes. It is
written under XDG_RUNTIME_DIR -- 0700, on tmpfs, gone at logout --
rather than /tmp, which is shared; the file is 0600; the passphrase is
piped to qrencode on stdin rather than passed as an argument, because
argv is world-readable through /proc for as long as the process runs;
and it is never printed or included in an error message. Generated on
demand, because producing a code for every saved network up front means
writing images of passwords nobody asked to see.

Enterprise networks are listed as not shareable rather than offered and
broken: there is no passphrase to encode, so the code could not work.

Two bugs the contract caught while being written. Semicolons in an SSID
were not escaped -- the sed replacement had one backslash where its four
neighbours have two, so sed dropped it, and an SSID containing a
semicolon would have produced a QR code describing a different network.
And nmcli's trailing newline landed inside the payload; it decoded here,
but a newline in the middle of a WIFI: URI is not something every phone
tolerates, and that failure would present as "the QR code just doesn't
work on my phone".

The contract stubs nmcli and qrencode, because the real ones would write
this machine's actual Wi-Fi password into a fixture directory. It
asserts the escaping, the absence of a newline, the file and directory
modes, that no temporary payload survives, and that the passphrase never
reaches argv.

Claude-Session: https://claude.ai/code/session_01BRvzt4H8XXLPVH5MyYdk9L

config/dot/quickshell/modules/settings/ConnectivityPage.qml

@@ -19,13 +19,18 @@ import qs.services
 SettingsPage {
     id: root
 
+
     title: "Network & Devices"
     lede: Connectivity.activeNetwork
         ? "Connected to " + Connectivity.activeNetwork.name
         : "Wi-Fi, Bluetooth, and the things Fedora owns."
 
     // Drive the scanners only while this page is the one being shown.
-    Component.onCompleted: Connectivity.active = true
+    Component.onCompleted: {
+        Connectivity.active = true;
+        if (!WifiShare.scanned)
+            WifiShare.refresh();
+    }
     Component.onDestruction: Connectivity.active = false
 
     SettingsCard {
@@ -68,6 +73,69 @@ SettingsPage {
         }
     }
 
+    // Sharing a network by QR, the way GNOME's Wi-Fi panel does. The
+    // alternative is reading a passphrase out loud.
+    //
+    // The image holds the password in machine-readable form, so it is generated
+    // on demand rather than up front, and the helper writes it to tmpfs under
+    // XDG_RUNTIME_DIR instead of anywhere persistent.
+    SettingsCard {
+        visible: Connectivity.wifiDevice !== null && WifiShare.shareable.length > 0
+        title: "Share a network"
+        subtitle: WifiShare.sharing !== ""
+            ? "Point a phone's camera at the code to join " + WifiShare.sharing + "."
+            : "Shows a QR code a phone can scan to join, without reading the password out."
+
+        Repeater {
+            model: WifiShare.shareable
+
+            ActionRow {
+                id: shareRow
+                required property var modelData
+                required property int index
+
+                label: shareRow.modelData.ssid
+                detail: WifiShare.sharing === shareRow.modelData.name
+                    ? "Showing a code below — anyone who can see the screen can join"
+                    : "Saved network"
+                action: WifiShare.sharing === shareRow.modelData.name ? "Hide" : "Show code"
+                divider: shareRow.index < WifiShare.shareable.length - 1 || WifiShare.sharing !== ""
+                onTriggered: WifiShare.sharing === shareRow.modelData.name
+                    ? WifiShare.stopSharing()
+                    : WifiShare.share(shareRow.modelData.name)
+            }
+        }
+
+        // Drawn at its natural size on a white plate: a QR code inverted or
+        // tinted to match a dark theme is unreliable to scan, and this one has
+        // exactly one job.
+        Item {
+            width: parent.width
+            visible: WifiShare.sharing !== "" && WifiShare.imagePath !== ""
+            implicitHeight: visible ? plate.height + 20 : 0
+
+            Rectangle {
+                id: plate
+                anchors.horizontalCenter: parent.horizontalCenter
+                y: 10
+                width: 208
+                height: 208
+                radius: 10
+                color: "white"
+
+                Image {
+                    anchors.centerIn: parent
+                    width: 184
+                    height: 184
+                    smooth: false
+                    fillMode: Image.PreserveAspectFit
+                    cache: false
+                    source: WifiShare.imagePath !== "" ? "file://" + WifiShare.imagePath : ""
+                }
+            }
+        }
+    }
+
     SettingsCard {
         title: "Bluetooth"
         visible: Connectivity.adapter !== null