fix(FN-1299): stabilize agent detail refresh callbacks

- Stabilize AgentDetailView callback usage by storing onClose/addToast in refs and removing them from loadAgent dependencies
- Prevent full-screen loading spinner on background refresh by only showing it before the initial agent load
- Memoize detail modal handlers in AgentsView to keep callback identities stable across parent re-renders
- Add regression tests covering callback identity churn and refresh behavior without loading-state flicker

packages/dashboard/app/components/AgentDetailView.tsx

@@ -84,19 +84,30 @@ export function AgentDetailView({ agentId, projectId, onClose, addToast, onChild
   const [activeTab, setActiveTab] = useState<TabId>("dashboard");
   const [isStreaming, setIsStreaming] = useState(false);
   const logContainerRef = useRef<HTMLDivElement>(null);
+  const onCloseRef = useRef(onClose);
+  const addToastRef = useRef(addToast);
+  const agentRef = useRef<AgentDetail | null>(null);
+
+  onCloseRef.current = onClose;
+  addToastRef.current = addToast;
+  agentRef.current = agent;
 
   const loadAgent = useCallback(async () => {
-    setIsLoading(true);
+    const showLoadingSpinner = agentRef.current === null;
+    if (showLoadingSpinner) {
+      setIsLoading(true);
+    }
+
     try {
       const data = await fetchAgent(agentId, projectId);
       setAgent(data);
     } catch (err: any) {
-      addToast(`Failed to load agent: ${err.message}`, "error");
-      onClose();
+      addToastRef.current(`Failed to load agent: ${err.message}`, "error");
+      onCloseRef.current();
     } finally {
       setIsLoading(false);
     }
-  }, [agentId, addToast, onClose, projectId]);
+  }, [agentId, projectId]);
 
   const loadLogs = useCallback(async () => {
     // Agent logs are tied to tasks, not agents directly.

packages/dashboard/app/components/AgentsView.tsx

@@ -343,6 +343,14 @@ export function AgentsView({ addToast, projectId }: AgentsViewProps) {
     }
   };
 
+  const handleCloseDetail = useCallback(() => {
+    setSelectedAgentId(null);
+  }, []);
+
+  const handleChildClick = useCallback((childId: string) => {
+    setSelectedAgentId(childId);
+  }, []);
+
   const handleRunHeartbeat = async (agentId: string, agentName: string) => {
     try {
       await startAgentRun(agentId, projectId, { source: "on_demand", triggerDetail: "Triggered from dashboard" });
@@ -942,9 +950,9 @@ export function AgentsView({ addToast, projectId }: AgentsViewProps) {
         <AgentDetailView
           agentId={selectedAgentId}
           projectId={projectId}
-          onClose={() => setSelectedAgentId(null)}
+          onClose={handleCloseDetail}
           addToast={addToast}
-          onChildClick={(childId) => setSelectedAgentId(childId)}
+          onChildClick={handleChildClick}
         />
       )}
 

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

@@ -272,6 +272,73 @@ describe("AgentDetailView", () => {
     });
   });
 
+  it("does not refetch or show loading spinner when onClose/addToast callback identities change", async () => {
+    const initialOnClose = vi.fn();
+    const initialAddToast = vi.fn();
+
+    const { rerender } = render(
+      <AgentDetailView
+        agentId="agent-001"
+        onClose={initialOnClose}
+        addToast={initialAddToast}
+      />,
+    );
+
+    await waitFor(() => {
+      expect(screen.getByRole("heading", { name: "Test Agent" })).toBeInTheDocument();
+    });
+    expect(mockFetchAgent).toHaveBeenCalledTimes(1);
+
+    rerender(
+      <AgentDetailView
+        agentId="agent-001"
+        onClose={vi.fn()}
+        addToast={vi.fn()}
+      />,
+    );
+
+    expect(mockFetchAgent).toHaveBeenCalledTimes(1);
+    expect(screen.queryByText("Loading agent...")).not.toBeInTheDocument();
+  });
+
+  it("refreshes agent data without showing full-screen loading spinner after initial load", async () => {
+    const user = userEvent.setup();
+    let resolveRefresh: ((value: AgentDetail) => void) | undefined;
+
+    mockFetchAgent
+      .mockImplementationOnce(async () => createMockAgent())
+      .mockImplementationOnce(
+        () =>
+          new Promise((resolve) => {
+            resolveRefresh = resolve;
+          }),
+      );
+
+    render(
+      <AgentDetailView
+        agentId="agent-001"
+        onClose={vi.fn()}
+        addToast={vi.fn()}
+      />,
+    );
+
+    await waitFor(() => {
+      expect(screen.getByRole("heading", { name: "Test Agent" })).toBeInTheDocument();
+    });
+
+    await user.click(screen.getByTitle("Refresh"));
+
+    await waitFor(() => {
+      expect(mockFetchAgent).toHaveBeenCalledTimes(2);
+    });
+    expect(screen.queryByText("Loading agent...")).not.toBeInTheDocument();
+
+    resolveRefresh?.(createMockAgent({ updatedAt: "2024-01-01T00:10:00.000Z" }));
+    await waitFor(() => {
+      expect(screen.getByRole("heading", { name: "Test Agent" })).toBeInTheDocument();
+    });
+  });
+
   it("displays role badge", async () => {
     render(
       <AgentDetailView