feat(FN-4147): add mobile-friendly github tracking enable button in header

Adds a GitHub tracking toggle affordance to the task detail header with accompanying tests, documentation updates, and a changeset, plus a CSS fix for mobile header wrapping.

Fusion-Task-Id: FN-4147

packages/dashboard/app/components/TaskDetailModal.css

@@ -436,12 +436,18 @@
   font-family: var(--font-mono);
 }
 
+.detail-github-tracking-enable {
+  margin-left: auto;
+  align-self: center;
+}
+
 .detail-source-toggle {
   display: inline-flex;
   align-items: center;
   justify-content: center;
-  min-width: 36px;
-  min-height: 36px;
+  flex-shrink: 0;
+  min-width: calc(var(--space-lg) + var(--space-xl) - var(--space-xs));
+  min-height: calc(var(--space-lg) + var(--space-xl) - var(--space-xs));
   padding: var(--space-xs);
   border: 0;
   border-radius: var(--radius-sm);
@@ -451,6 +457,10 @@
   transition: background var(--transition-fast), color var(--transition-fast);
 }
 
+.detail-source-header .detail-source-toggle {
+  margin-left: var(--space-sm);
+}
+
 .detail-source-toggle:hover {
   color: var(--text);
   background: var(--card-hover);
@@ -1576,12 +1586,23 @@
 
   .detail-source-header {
     align-items: flex-start;
+    flex-wrap: wrap;
   }
 
   .detail-source-summary {
+    flex: 1 1 100%;
     flex-wrap: wrap;
   }
 
+  .detail-github-tracking-enable {
+    margin-left: auto;
+    justify-content: center;
+  }
+
+  .detail-source-header .detail-source-toggle {
+    margin-left: 0;
+  }
+
   .detail-body {
     padding: calc(var(--space-md) + var(--space-xs) / 2);
     overflow-x: hidden;

packages/dashboard/app/components/TaskDetailModal.tsx

@@ -2391,6 +2391,17 @@ export function TaskDetailContent({
                     </span>
                   )}
                 </div>
+                {canEditGithubTracking && !githubTrackingEnabled && !githubTrackedIssue && !isSavingGithubTracking && (
+                  <button
+                    type="button"
+                    className="btn btn-sm btn-primary touch-target detail-github-tracking-enable"
+                    aria-label="Enable GitHub tracking"
+                    onClick={() => void handleToggleGithubTracking()}
+                    disabled={isSavingGithubTracking}
+                  >
+                    Enable GitHub tracking
+                  </button>
+                )}
                 <button
                   type="button"
                   className="detail-source-toggle"

packages/dashboard/app/components/__tests__/TaskDetailModal.inline-editing-and-integrations.test.tsx

@@ -2203,7 +2203,90 @@ describe("TaskDetailModal", () => {
 
       expect(screen.getByText("GitHub tracking")).toBeTruthy();
       expect(screen.getByText("Tracking is currently disabled")).toBeTruthy();
-      expect(screen.queryByLabelText("Enable GitHub tracking")).toBeNull();
+      expect(screen.getByRole("button", { name: "Enable GitHub tracking" })).toBeInTheDocument();
+    });
+
+    it("enables GitHub tracking via the inline header button without expanding the disclosure", async () => {
+      const { updateTask } = await import("../../api");
+      const mockUpdate = vi.mocked(updateTask);
+      const addToast = vi.fn();
+      mockUpdate.mockResolvedValueOnce({ id: "FN-001" } as Task);
+
+      render(
+        <TaskDetailModal
+          task={makeTask({
+            id: "FN-001",
+            column: "todo",
+            githubTracking: {
+              enabled: false,
+            },
+          })}
+          onClose={noop}
+          onOpenDetail={noopOpenDetail}
+          onMoveTask={noopMove}
+          onDeleteTask={noopDelete}
+          onMergeTask={noopMerge}
+          addToast={addToast}
+        />,
+      );
+
+      const expandButton = screen.getByRole("button", { name: "Expand GitHub tracking details" });
+      expect(expandButton).toHaveAttribute("aria-expanded", "false");
+
+      fireEvent.click(screen.getByRole("button", { name: "Enable GitHub tracking" }));
+
+      await waitFor(() => {
+        expect(mockUpdate).toHaveBeenCalledWith("FN-001", { githubTracking: { enabled: true } }, undefined);
+      });
+      expect(addToast).not.toHaveBeenCalledWith(expect.stringContaining("Failed to update FN-001"), "error");
+      expect(screen.getByRole("button", { name: "Expand GitHub tracking details" })).toHaveAttribute("aria-expanded", "false");
+      expect(screen.queryByRole("button", { name: "Collapse GitHub tracking details" })).toBeNull();
+    });
+
+    it("hides the inline enable button when tracking is already enabled", () => {
+      render(
+        <TaskDetailModal
+          task={makeTask({ column: "todo", githubTracking: { enabled: true } })}
+          onClose={noop}
+          onOpenDetail={noopOpenDetail}
+          onMoveTask={noopMove}
+          onDeleteTask={noopDelete}
+          onMergeTask={noopMerge}
+          addToast={noop}
+        />,
+      );
+
+      expect(screen.queryByRole("button", { name: "Enable GitHub tracking" })).toBeNull();
+      expect(screen.getByRole("button", { name: "Expand GitHub tracking details" })).toBeInTheDocument();
+    });
+
+    it("hides the inline enable button when an issue is already linked", () => {
+      render(
+        <TaskDetailModal
+          task={makeTask({
+            column: "todo",
+            githubTracking: {
+              enabled: false,
+              issue: {
+                owner: "runfusion",
+                repo: "fusion",
+                number: 456,
+                url: "https://github.com/runfusion/fusion/issues/456",
+                createdAt: "2026-01-01T00:00:00Z",
+              },
+            },
+          })}
+          onClose={noop}
+          onOpenDetail={noopOpenDetail}
+          onMoveTask={noopMove}
+          onDeleteTask={noopDelete}
+          onMergeTask={noopMerge}
+          addToast={noop}
+        />,
+      );
+
+      expect(screen.queryByRole("button", { name: "Enable GitHub tracking" })).toBeNull();
+      expect(screen.getByRole("button", { name: "Expand GitHub tracking details" })).toBeInTheDocument();
     });
 
     it("hides section when tracking is disabled and task is not in an eligible column", () => {