FN-7342: preserve board scroll during refresh stabilization

Board stabilization now avoids resetting the user's horizontal column position during refresh and resize handling.

- Keep mobile stabilization focused on document-level drift instead of forcing #board.scrollLeft back to triage.
- Add regression coverage for board and all-workflows scroll preservation across task refresh, window resize, and visualViewport resize.
- Add a patch changeset for the published Fusion package.

Files changed:
 .changeset/fn-7342-board-scroll-reset.md           |   7 ++
 packages/dashboard/app/components/Board.tsx        |   7 +-
 .../app/components/__tests__/Board.test.tsx        | 109 +++++++++++++++++++++
 3 files changed, 121 insertions(+), 2 deletions(-)

Fusion-Task-Id: FN-7342

Fusion-Task-Lineage: 0aa8b152-5cc0-4f77-93d5-f20faf0a5e19

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>

.changeset/fn-7342-board-scroll-reset.md

@@ -0,0 +1,7 @@
+---
+"@runfusion/fusion": patch
+---
+
+summary: Preserve board column scroll during dashboard refresh and viewport stabilization.
+category: fix
+dev: Narrows mobile board stabilization so task/workflow refresh and resize events pin document drift without resetting #board.scrollLeft.

packages/dashboard/app/components/Board.tsx

@@ -261,11 +261,15 @@ export function Board({ tasks, projectId, maxConcurrent, showWorktreeGrouping, o
     return stableGrouped;
   }, [tasks, doneSortMode]);
 
+  /*
+  FNXC:BoardNavigation 2026-06-30-17:42:
+  Periodic task/workflow refreshes, rerenders, window resize, and visualViewport resize must not override intentional board-column scroll while the Board is already visible. Keep FN-001/FN-4574 stabilization focused on page-level horizontal drift and layout reflow; #board is the user's horizontal scroller, so it must not be forced back to triage.
+  */
   // FN-4574 + FN-001 diagnosis: on iOS Safari, the mobile board can occasionally
   // snap against stale layout/visualViewport metrics before flex columns resolve,
   // both on initial mount and on pageshow/bfcache restore after backgrounding.
   // We keep the FN-001 baseline (`scroll-snap-type: x proximity` +
-  // `overflow-anchor: none`) and only stabilize via reflow + scroll offset
+  // `overflow-anchor: none`) and only stabilize via reflow + document scroll
   // normalization; do NOT reintroduce `scroll-snap-type: x mandatory`.
   useEffect(() => {
     const mobileQuery = window.matchMedia(MOBILE_MEDIA_QUERY);
@@ -278,7 +282,6 @@ export function Board({ tasks, projectId, maxConcurrent, showWorktreeGrouping, o
       void boardEl.offsetWidth;
       if (mobileQuery.matches) {
         resetDocumentHorizontalScroll();
-        boardEl.scrollLeft = 0;
       }
     };
 

packages/dashboard/app/components/__tests__/Board.test.tsx

@@ -199,6 +199,49 @@ function renderBoard(props = {}) {
   return render(<Board {...createBoardProps(props)} />);
 }
 
+function installMobileBoardStabilizationHarness() {
+  const originalMatchMedia = window.matchMedia;
+  const originalRequestAnimationFrame = window.requestAnimationFrame;
+  const originalCancelAnimationFrame = window.cancelAnimationFrame;
+  const visualViewportDescriptor = Object.getOwnPropertyDescriptor(window, "visualViewport");
+  const visualViewportTarget = new EventTarget() as EventTarget & { scale: number };
+  visualViewportTarget.scale = 1;
+
+  window.matchMedia = vi.fn().mockImplementation((query: string) => ({
+    matches: query.includes("768px"),
+    media: query,
+    onchange: null,
+    addEventListener: vi.fn(),
+    removeEventListener: vi.fn(),
+    addListener: vi.fn(),
+    removeListener: vi.fn(),
+    dispatchEvent: vi.fn(),
+  }));
+  window.requestAnimationFrame = vi.fn((callback: FrameRequestCallback) => {
+    callback(performance.now());
+    return 1;
+  });
+  window.cancelAnimationFrame = vi.fn();
+  Object.defineProperty(window, "visualViewport", {
+    configurable: true,
+    value: visualViewportTarget,
+  });
+
+  return {
+    visualViewport: visualViewportTarget,
+    restore() {
+      window.matchMedia = originalMatchMedia;
+      window.requestAnimationFrame = originalRequestAnimationFrame;
+      window.cancelAnimationFrame = originalCancelAnimationFrame;
+      if (visualViewportDescriptor) {
+        Object.defineProperty(window, "visualViewport", visualViewportDescriptor);
+      } else {
+        delete (window as typeof window & { visualViewport?: VisualViewport }).visualViewport;
+      }
+    },
+  };
+}
+
 async function openWorkflowSwitcher() {
   const trigger = await screen.findByTestId("workflow-switcher");
   fireEvent.click(trigger);
@@ -224,6 +267,46 @@ describe("Board", () => {
     expect(main.id).toBe("board");
   });
 
+  it("preserves intentional board column scroll during mobile resize stabilization", () => {
+    const harness = installMobileBoardStabilizationHarness();
+    try {
+      const { rerender } = renderBoard({
+        tasks: [
+          { id: "FN-SCROLL-1", description: "Later lane", column: "in-review", dependencies: [], steps: [], currentStep: 0, log: [], createdAt: "2024-01-01T00:00:00.000Z", updatedAt: "2024-01-01T00:00:00.000Z" } as Task,
+        ],
+      });
+      const board = screen.getByRole("main") as HTMLElement;
+      board.scrollLeft = 360;
+
+      rerender(<Board {...createBoardProps({ tasks: [] })} />);
+      act(() => {
+        window.dispatchEvent(new Event("resize"));
+      });
+
+      expect(board.scrollLeft).toBe(360);
+      expect(document.documentElement.scrollLeft).toBe(0);
+    } finally {
+      harness.restore();
+    }
+  });
+
+  it("preserves intentional board column scroll during mobile visualViewport stabilization", () => {
+    const harness = installMobileBoardStabilizationHarness();
+    try {
+      renderBoard();
+      const board = screen.getByRole("main") as HTMLElement;
+      board.scrollLeft = 480;
+
+      act(() => {
+        harness.visualViewport.dispatchEvent(new Event("resize"));
+      });
+
+      expect(board.scrollLeft).toBe(480);
+    } finally {
+      harness.restore();
+    }
+  });
+
   it("FN-4380: does not eagerly fetch GitHub badge status on board mount", () => {
     vi.useFakeTimers();
     try {
@@ -1666,6 +1749,32 @@ describe("Board", () => {
       ]);
     });
 
+    it("preserves all-workflows board scroll during mobile visualViewport refresh stabilization", async () => {
+      const harness = installMobileBoardStabilizationHarness();
+      try {
+        enableFlag(
+          { "FN-1": "builtin:coding", "FN-2": "wf-custom" },
+          [DEFAULT_WORKFLOW, CUSTOM_WORKFLOW],
+        );
+        renderBoard({ tasks: [mkTask({ id: "FN-1", column: "todo" }), mkTask({ id: "FN-2", column: "intake" })] });
+
+        await selectWorkflow(ALL_WORKFLOWS_BOARD_VIEW_ID);
+        const board = screen.getByRole("main") as HTMLElement;
+        expect(board.className).toContain("board-workflow-columns");
+        board.scrollLeft = 520;
+
+        act(() => {
+          harness.visualViewport.dispatchEvent(new Event("resize"));
+          window.dispatchEvent(new Event("resize"));
+        });
+
+        expect(board.scrollLeft).toBe(520);
+        expect(screen.getByTestId("column-intake")).toHaveAttribute("data-tasks", expect.stringContaining("FN-2"));
+      } finally {
+        harness.restore();
+      }
+    });
+
     it("archived column is collapsible in workflow mode", async () => {
       enableFlag({ "FN-9": "builtin:coding" });
       renderBoard({ tasks: [mkTask({ id: "FN-9", column: "archived" })] });