FN-6863: raise footer concurrency slider limits

Raise the footer engine control sliders to support higher concurrency without hiding persisted values.

- Increase max tasks, max triage, and max worktree slider baselines to 50.
- Preserve value-aware slider maxima for persisted settings above the new baseline.
- Add coverage for in-range 50 limits, above-range persisted values, and saving a value of 50.

Files changed:
 .../dashboard/app/components/EngineControlMenu.tsx |  9 ++--
 .../__tests__/EngineControlMenu.test.tsx           | 50 +++++++++++++++++++---
 2 files changed, 49 insertions(+), 10 deletions(-)

Fusion-Task-Id: FN-6863

Fusion-Task-Lineage: f42373fc-322b-4d20-9b8b-2d0c63254e79

packages/dashboard/app/components/EngineControlMenu.tsx

@@ -35,9 +35,9 @@ const DEFAULT_CONCURRENCY_VALUES: ConcurrencyValues = {
 };
 
 const CONCURRENCY_SLIDER_LIMITS: Record<keyof ConcurrencyValues, { min: number; max: number }> = {
-  maxConcurrent: { min: 1, max: 10 },
-  maxTriageConcurrent: { min: 1, max: 10 },
-  maxWorktrees: { min: 1, max: 20 },
+  maxConcurrent: { min: 1, max: 50 },
+  maxTriageConcurrent: { min: 1, max: 50 },
+  maxWorktrees: { min: 1, max: 50 },
 };
 
 function clamp(value: number, min: number, max: number) {
@@ -58,6 +58,9 @@ Engine stop/start, triage pause/resume, and live scheduler concurrency/worktree
 
 FNXC:EngineControls 2026-06-21-00:00:
 FN-6862 requires the footer popover chrome to stay opaque across themes. Its CSS must use a defined solid surface token (`var(--card)`) because `--surface-elevated` is not in the dashboard token vocabulary and makes the menu transparent when unresolved.
+
+FNXC:EngineControls 2026-06-21-00:00:
+FN-6863 raises the footer concurrency sliders' base drag ceiling to 50 for max tasks, triage, and worktrees. Keep getConcurrencySliderMax value-aware so already-persisted settings above 50 expand the slider instead of hiding or clamping the truthful readout.
 */
 export const EngineControlMenu = forwardRef<EngineControlMenuHandle, EngineControlMenuProps>(function EngineControlMenu({ projectId }, ref) {
   const { t } = useTranslation("app");

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

@@ -104,9 +104,9 @@ describe("EngineControlMenu", () => {
   it("persists debounced concurrency and worktree slider changes and refreshes settings", async () => {
     legacyMocks.fetchSettings.mockResolvedValue({
       ...defaultSettings,
-      maxConcurrent: 12,
-      maxTriageConcurrent: 3,
-      maxWorktrees: 25,
+      maxConcurrent: 60,
+      maxTriageConcurrent: 70,
+      maxWorktrees: 80,
     });
     await openMenu();
 
@@ -116,10 +116,12 @@ describe("EngineControlMenu", () => {
 
     vi.useFakeTimers();
 
-    expect(maxConcurrent).toHaveAttribute("max", "12");
-    expect(maxConcurrent).toHaveValue("12");
-    expect(maxWorktrees).toHaveAttribute("max", "25");
-    expect(maxWorktrees).toHaveValue("25");
+    expect(maxConcurrent).toHaveAttribute("max", "60");
+    expect(maxConcurrent).toHaveValue("60");
+    expect(maxTriage).toHaveAttribute("max", "70");
+    expect(maxTriage).toHaveValue("70");
+    expect(maxWorktrees).toHaveAttribute("max", "80");
+    expect(maxWorktrees).toHaveValue("80");
 
     fireEvent.change(maxConcurrent, { target: { value: "9" } });
     fireEvent.change(maxTriage, { target: { value: "4" } });
@@ -136,6 +138,40 @@ describe("EngineControlMenu", () => {
     expect(apiMocks.fetchSettings).toHaveBeenCalledTimes(2);
   });
 
+  it("uses a 50 max for all in-range concurrency sliders", async () => {
+    legacyMocks.fetchSettings.mockResolvedValue({
+      ...defaultSettings,
+      maxConcurrent: 12,
+      maxTriageConcurrent: 3,
+      maxWorktrees: 25,
+    });
+    await openMenu();
+
+    expect(await screen.findByLabelText(/max concurrent tasks/i)).toHaveAttribute("max", "50");
+    expect(screen.getByLabelText(/max triage concurrent/i)).toHaveAttribute("max", "50");
+    expect(screen.getByLabelText(/max worktrees/i)).toHaveAttribute("max", "50");
+  });
+
+  it("persists a slider value of 50 through the debounced settings save", async () => {
+    await openMenu();
+
+    const maxConcurrent = await screen.findByLabelText(/max concurrent tasks/i);
+    vi.useFakeTimers();
+
+    expect(maxConcurrent).toHaveAttribute("max", "50");
+
+    fireEvent.change(maxConcurrent, { target: { value: "50" } });
+
+    await act(async () => {
+      await vi.advanceTimersByTimeAsync(500);
+    });
+
+    expect(legacyMocks.updateSettings).toHaveBeenCalledWith(
+      { maxConcurrent: 50, maxTriageConcurrent: 1, maxWorktrees: 4 },
+      "proj_123",
+    );
+  });
+
   it("renders a load error state without crashing", async () => {
     legacyMocks.fetchSettings.mockRejectedValue(new Error("settings unavailable"));
     await openMenu();