FN-5751: fix dashboard auto-merge toggle race

Prevent rapid auto-merge toggles from desynchronizing dashboard settings state.

- Track auto-merge state in a ref so each toggle reads and writes the latest value
- Apply optimistic updates from the ref and roll back correctly on failed setting updates
- Add regression coverage for rapid double-toggle behavior in useAppSettings
- Add a patch changeset for @runfusion/fusion describing the dashboard blank-state fix

Files changed:
 .changeset/fn-5751-auto-merge-toggle.md            |  5 ++++
 .../app/hooks/__tests__/useAppSettings.test.ts     | 27 ++++++++++++++++++++++
 packages/dashboard/app/hooks/useAppSettings.ts     | 20 +++++++++++-----
 3 files changed, 46 insertions(+), 6 deletions(-)

Fusion-Task-Id: FN-5751

Fusion-Task-Lineage: 1a0090ff-4015-46b8-a974-3accbbdce919

.changeset/fn-5751-auto-merge-toggle.md

@@ -0,0 +1,5 @@
+---
+"@runfusion/fusion": patch
+---
+
+Fixes a dashboard regression where toggling the in-review Auto-merge switch could leave the UI in a broken/blank state until refresh. Auto-merge toggle state updates now remain consistent during rapid toggles, and regression coverage was added for the settings hook path.

packages/dashboard/app/hooks/__tests__/useAppSettings.test.ts

@@ -75,6 +75,33 @@ describe("useAppSettings", () => {
     expect(mockUpdateSettings).toHaveBeenCalledWith({ autoMerge: true }, "proj_123");
   });
 
+  it("preserves consistent autoMerge state across rapid toggles", async () => {
+    const updateResolvers: Array<() => void> = [];
+    mockUpdateSettings.mockImplementation(
+      () => new Promise((resolve) => updateResolvers.push(() => resolve({} as never))),
+    );
+
+    const { result } = renderHook(() => useAppSettings("proj_123"));
+
+    await waitFor(() => {
+      expect(result.current.autoMerge).toBe(false);
+    });
+
+    await act(async () => {
+      const firstToggle = result.current.toggleAutoMerge();
+      const secondToggle = result.current.toggleAutoMerge();
+
+      expect(result.current.autoMerge).toBe(false);
+
+      updateResolvers.forEach((resolve) => resolve());
+      await Promise.all([firstToggle, secondToggle]);
+    });
+
+    expect(mockUpdateSettings).toHaveBeenNthCalledWith(1, { autoMerge: true }, "proj_123");
+    expect(mockUpdateSettings).toHaveBeenNthCalledWith(2, { autoMerge: false }, "proj_123");
+    expect(result.current.autoMerge).toBe(false);
+  });
+
   it("rolls back optimistic state when toggle update fails", async () => {
     mockUpdateSettings.mockRejectedValueOnce(new Error("network"));
 

packages/dashboard/app/hooks/useAppSettings.ts

@@ -1,4 +1,4 @@
-import { useCallback, useEffect, useState } from "react";
+import { useCallback, useEffect, useRef, useState } from "react";
 import { fetchConfig, fetchSettings, updateSettings, updateGlobalSettings } from "../api";
 import { setAutoReloadEnabled } from "../versionCheck";
 
@@ -63,6 +63,7 @@ export function useAppSettings(projectId?: string): UseAppSettingsResult {
   const [todosEnabled, setTodosEnabled] = useState(false);
   const [goalsEnabled, setGoalsEnabled] = useState(false);
   const [autoReloadOnVersionChange, setAutoReloadOnVersionChangeState] = useState(true);
+  const autoMergeRef = useRef(autoMerge);
 
   /**
    * Fetches config and settings from the backend and updates local state.
@@ -124,16 +125,23 @@ export function useAppSettings(projectId?: string): UseAppSettingsResult {
     void refresh();
   }, [refresh]);
 
+  useEffect(() => {
+    autoMergeRef.current = autoMerge;
+  }, [autoMerge]);
+
   const toggleAutoMerge = useCallback(async () => {
-    const next = !autoMerge;
-    setAutoMerge(next);
+    const previousAutoMerge = autoMergeRef.current;
+    const nextAutoMerge = !previousAutoMerge;
+    autoMergeRef.current = nextAutoMerge;
+    setAutoMerge(nextAutoMerge);
 
     try {
-      await updateSettings({ autoMerge: next }, projectId);
+      await updateSettings({ autoMerge: nextAutoMerge }, projectId);
     } catch {
-      setAutoMerge(!next);
+      autoMergeRef.current = previousAutoMerge;
+      setAutoMerge(previousAutoMerge);
     }
-  }, [autoMerge, projectId]);
+  }, [projectId]);
 
   const toggleGlobalPause = useCallback(async () => {
     const next = !globalPaused;