shell: resolve logind session via User.Display, re-register after sessiond restart

SessionEvents asked loginctl for -p ObjectPath, which is not a property — it
returned empty on every boot, so external lock signals were never monitored and
the shell had no unlock ingress. Resolve the graphical session the way
lockhint.rs does; not GetSession(auto) (this shell is a session-less user unit)
and not the /session/auto alias (PropertiesChanged only fires on the concrete
path).

SessiondBridge read root.registered to decide whether to re-register on
reconnect, but the disconnect branch had already cleared it, so the shell never
re-registered after a sessiond restart. Latch it.

surfaces/quickshell/services/SessionEvents.qml

@@ -76,38 +76,43 @@ Singleton {
     signal sleepInhibitorAcquired()
 
     // --- Session path resolution -------------------------------------------
-    // The logind session D-Bus object path contains the session ID with dots
+    // Resolve the graphical session's REAL object path via the user's `Display`
-    // replaced by underscores (session "3" -> /org/freedesktop/login1/session/_3,
+    // session. sessiond resolves exactly this way; see the two measured traps
-    // session "c1" -> /org/freedesktop/login1/session/_c1). We resolve it once
+    // documented on `resolve_session_path` in src/sessiond/lockhint.rs:
-    // at startup by asking logind for the current session's object path.
+    //
+    //   Not `auto`. `GetSession("auto")` resolves to the CALLER's session, and
+    //   this shell is a systemd user unit under user@1000.service, outside any
+    //   session scope — it has no session of its own to name.
+    //
+    //   Not the `auto` path either. /org/freedesktop/login1/session/auto is an
+    //   alias, not an object: PropertiesChanged only fires on the concrete
+    //   path, so monitoring the alias subscribes to something never delivered.
+    //
+    // The user's `Display` session is the graphical one by definition, whoever
+    // asks. The previous probe here asked for a `-p ObjectPath` property that
+    // loginctl does not have, so it returned empty on every boot and external
+    // lock signals were never monitored at all.
     Process {
         id: sessionResolver
         running: true
         command: ["sh", "-c",
-            // loginctl list-sessions -p Name gives the first session's user;
+            "busctl --system get-property org.freedesktop.login1 "
-            // show-session with no argument operates on the caller's session.
+            + "/org/freedesktop/login1/user/_$(id -u) "
-            // -p ObjectPath gives the D-Bus path directly, no encoding needed.
+            + "org.freedesktop.login1.User Display 2>/dev/null"]
-            "loginctl show-session -p ObjectPath 2>/dev/null | head -1"]
         stdout: StdioCollector {
             onStreamFinished: {
                 const raw = text.trim();
-                // loginctl outputs ObjectPath=/org/freedesktop/login1/session/_3
+                // `(so) "1" "/org/freedesktop/login1/session/_31"` — the object
-                const match = raw.match(/^ObjectPath=(.+)$/);
+                // path is the second quoted field.
-                if (match && match[1].length > 0) {
+                const path = raw.split('"')[3];
-                    root.sessionPath = match[1];
+                if (path && path.startsWith("/org/freedesktop/login1/session/")) {
+                    root.sessionPath = path;
                     console.log("[session-events] session path:", root.sessionPath);
                     sessionLockMonitor.running = true;
                 } else if (raw.length > 0) {
-                    // Some logind versions print just the path without the key.
+                    console.log("[session-events] could not parse Display session from:", raw);
-                    if (raw.startsWith("/org/freedesktop/login1/session/")) {
-                        root.sessionPath = raw;
-                        console.log("[session-events] session path (bare):", root.sessionPath);
-                        sessionLockMonitor.running = true;
-                    } else {
-                        console.log("[session-events] could not parse session path from:", raw);
-                    }
                 } else {
-                    console.log("[session-events] no session path returned; "
+                    console.log("[session-events] no Display session for this user; "
                         + "external lock signals will not be monitored");
                 }
             }

surfaces/quickshell/services/SessiondBridge.qml

@@ -28,6 +28,10 @@ Singleton {
 
     // Registered = shell_ready was answered ok on the CURRENT connection.
     property bool registered: false
+    // Latched copy of `registered` taken when the connection drops. The
+    // disconnect branch clears `registered` before the reconnect branch runs,
+    // so reconnect cannot read it directly to decide whether to re-register.
+    property bool wasRegistered: false
     // sessiond held the session lock when we registered; we owe it a lock
     // and a locked_ack.
     property bool oweLock: false
@@ -112,8 +116,9 @@ Singleton {
         onConnectionStateChanged: {
             if (sock.connected) {
                 console.log("[sessiond-bridge] connected");
-                const wasRegistered = root.registered;
+                const wasRegistered = root.wasRegistered;
                 root.registered = false;
+                root.wasRegistered = false;
                 root.ackSent = false;
                 if (wasRegistered) {
                     root.shellReady(function(mustLock) {
@@ -126,6 +131,7 @@ Singleton {
                 }
             } else {
                 console.log("[sessiond-bridge] disconnected");
+                root.wasRegistered = root.registered;
                 root.registered = false;
                 root.pendingReady = null;
             }