Tier 0: render what the services already decided, honestly

Claude-Session: https://claude.ai/code/session_01Ms2FbjQy31TVf3CEvQhGM8

config/dot/quickshell/settings-system-harness.qml

@@ -12,6 +12,11 @@ ShellRoot {
     property var appliedBatches: []
     property bool displayBlocked: false
 
+    // The held-open safety snapshot: `pendingSnapshotDone` is the completion
+    // callback restoreDefaults handed over, waiting for the contract to answer.
+    property var pendingSnapshotDone: null
+    property bool snapshotRefusesToStart: false
+
     function recordReset(name: string): void {
         const next = root.resetCalls.slice();
         next.push(name);
@@ -43,10 +48,16 @@ ShellRoot {
             root.recordReset("display.block:" + blocked);
             root.displayBlocked = blocked;
         };
-        // Recorded so the contract can prove the snapshot happens BEFORE the
-        // stores are cleared, not merely that it happens.
-        SystemSettings.takeSafetySnapshot = function() {
-            root.recordReset("snapshot");
+        // The real snapshot is another process reading settings.json, so the
+        // stub is held open rather than answering inline: the contract drives
+        // its completion by hand and can therefore prove that nothing is wiped
+        // in the window between "snapshot started" and "snapshot finished",
+        // and that a failed snapshot leaves the stores alone.
+        SystemSettings.takeSafetySnapshot = function(done) {
+            root.recordReset("snapshot.start");
+            if (root.snapshotRefusesToStart)
+                return false;
+            root.pendingSnapshotDone = done;
             return true;
         };
         SystemSettings.reloadKeybinds = function() { root.recordReset("keybinds.reload"); };
@@ -107,6 +118,33 @@ ShellRoot {
             return SystemSettings.restoreDefaults();
         }
 
+        // Whether the next safety snapshot is allowed to start at all -- the
+        // "a backup is already running" case, which must refuse the reset
+        // outright rather than proceed without one.
+        function snapshotCanStart(allowed: bool): void {
+            root.snapshotRefusesToStart = !allowed;
+        }
+
+        // Answer the snapshot that restoreDefaults is waiting on. Everything
+        // the reset does must happen after this and not before.
+        function finishSnapshot(success: bool): bool {
+            const done = root.pendingSnapshotDone;
+            if (!done)
+                return false;
+            root.pendingSnapshotDone = null;
+            root.recordReset("snapshot.finish:" + success);
+            done(success);
+            return true;
+        }
+
+        function resetPending(): bool {
+            return SystemSettings.resetPending;
+        }
+
+        function clearError(): void {
+            SystemSettings.lastError = "";
+        }
+
         function resetState(): string {
             return JSON.stringify({
                 calls: root.resetCalls,