fix(panel): agent detail survives a stopped agent — fatal card only on a real roster miss

GET /orchestrator/agents/{id} 404s for any non-running container, and
the page's error early-return unmounted the DB-backed header/activity
content #529 had placed behind it. The fatal card now gates on the
roster identity lookup; a live-status error degrades in place to a
not-running banner + spawn dialog, with retry disabled on the
deterministic 404.

panel/src/app/(dashboard)/agents/[agentId]/__tests__/page.test.tsx

@@ -6,6 +6,13 @@ import { render, screen } from "@testing-library/react";
 // spawnAgent.mutateAsync({ agentId }) directly from a bare button — no task,
 // no message, no double-fire guard. Both bare buttons must now render the
 // shared SpawnAgentDialog instead.
+//
+// Whole-page-replaced-by-error fix: a stopped agent's live-status query 404s
+// (orchestrator has no running instance) while the agent's roster identity
+// still resolves fine. That must degrade the live-status area only — not
+// discard the DB-backed header/activity content already rendered above it.
+// The full-page fatal card is reserved for a genuinely invalid agent id
+// (the roster lookup itself failing).
 
 vi.mock("next/navigation", () => ({
   useParams: () => ({ agentId: "fe-dev-2" }),
@@ -24,15 +31,19 @@ vi.mock("@/hooks/use-page-refresh", () => ({
 
 vi.mock("@/hooks/use-agents", () => ({
   useAgentStatus: vi.fn(),
-  useAgentDefinition: vi.fn(() => ({ data: undefined })),
+  useAgentDefinition: vi.fn(() => ({
+    data: undefined,
+    isLoading: false,
+    error: undefined,
+  })),
   useStopAgent: vi.fn(() => ({ mutateAsync: vi.fn() })),
 }));
 
 vi.mock("@/components/agents", () => ({
-  AgentStatusCards: () => null,
+  AgentStatusCards: () => <div data-testid="agent-status-cards" />,
   ResolveWaitDialog: () => null,
   AgentStreamViewer: () => null,
-  AgentActivityPanel: () => null,
+  AgentActivityPanel: () => <div data-testid="agent-activity-panel" />,
   SpawnAgentDialog: ({
     agentId,
     agentName,
@@ -52,27 +63,10 @@ vi.mock("@/components/agents", () => ({
   ),
 }));
 
-import { useAgentStatus } from "@/hooks/use-agents";
+import { useAgentStatus, useAgentDefinition } from "@/hooks/use-agents";
 import AgentDetailPage from "../page";
 
 describe("AgentDetailPage — spawn dialog parity", () => {
-  it("renders SpawnAgentDialog (not a bare button) in the error state", () => {
-    vi.mocked(useAgentStatus).mockReturnValue({
-      data: undefined,
-      isLoading: false,
-      error: new Error("not found"),
-      refetch: vi.fn(),
-    } as unknown as ReturnType<typeof useAgentStatus>);
-
-    render(<AgentDetailPage />);
-
-    const dialog = screen.getByTestId("spawn-agent-dialog");
-    expect(dialog).toHaveAttribute("data-agent-id", "fe-dev-2");
-    expect(
-      screen.getByRole("button", { name: /Spawn Agent/i }),
-    ).toBeInTheDocument();
-  });
-
   it("renders SpawnAgentDialog in the header when the agent is not active", () => {
     vi.mocked(useAgentStatus).mockReturnValue({
       data: {
@@ -99,3 +93,81 @@ describe("AgentDetailPage — spawn dialog parity", () => {
     ).not.toBeInTheDocument();
   });
 });
+
+describe("AgentDetailPage — live-status error degrades, doesn't discard content", () => {
+  it("keeps header + activity panel and shows a not-running banner when the roster resolves but live status 404s", () => {
+    vi.mocked(useAgentDefinition).mockReturnValue({
+      data: { id: "fe-dev-2", uuid: "uuid-1", name: "Frontend Dev 2" },
+      isLoading: false,
+      error: undefined,
+    } as unknown as ReturnType<typeof useAgentDefinition>);
+    vi.mocked(useAgentStatus).mockReturnValue({
+      data: undefined,
+      isLoading: false,
+      error: new Error("Agent fe-dev-2 not found"),
+      refetch: vi.fn(),
+    } as unknown as ReturnType<typeof useAgentStatus>);
+
+    render(<AgentDetailPage />);
+
+    // DB-backed content that loaded independently of live status must stay.
+    expect(screen.getByText("Frontend Dev 2")).toBeInTheDocument();
+    expect(screen.getByTestId("agent-activity-panel")).toBeInTheDocument();
+
+    // Live-status area degrades to an inline banner, not a whole-page card.
+    expect(screen.getByText("Not running")).toBeInTheDocument();
+    expect(
+      screen.queryByText("Failed to load agent status"),
+    ).not.toBeInTheDocument();
+    expect(screen.queryByTestId("agent-status-cards")).not.toBeInTheDocument();
+    expect(
+      screen.getByRole("button", { name: /Spawn Agent/i }),
+    ).toBeInTheDocument();
+  });
+
+  it("shows the whole-page fatal card only when the roster lookup itself fails (invalid id)", () => {
+    vi.mocked(useAgentDefinition).mockReturnValue({
+      data: undefined,
+      isLoading: false,
+      error: new Error("Agent not found"),
+    } as unknown as ReturnType<typeof useAgentDefinition>);
+    vi.mocked(useAgentStatus).mockReturnValue({
+      data: undefined,
+      isLoading: false,
+      error: new Error("Agent not found"),
+      refetch: vi.fn(),
+    } as unknown as ReturnType<typeof useAgentStatus>);
+
+    render(<AgentDetailPage />);
+
+    expect(screen.getByText("Failed to load agent status")).toBeInTheDocument();
+    expect(
+      screen.queryByTestId("agent-activity-panel"),
+    ).not.toBeInTheDocument();
+    expect(
+      screen.getByRole("button", { name: /Spawn Agent/i }),
+    ).toBeInTheDocument();
+  });
+
+  it("shows the status skeleton (not the banner) while the roster is still loading, even if status already errored", () => {
+    vi.mocked(useAgentDefinition).mockReturnValue({
+      data: undefined,
+      isLoading: true,
+      error: undefined,
+    } as unknown as ReturnType<typeof useAgentDefinition>);
+    vi.mocked(useAgentStatus).mockReturnValue({
+      data: undefined,
+      isLoading: false,
+      error: new Error("Agent not found"),
+      refetch: vi.fn(),
+    } as unknown as ReturnType<typeof useAgentStatus>);
+
+    render(<AgentDetailPage />);
+
+    // Definition still resolving — not fatal yet, page renders normally.
+    expect(
+      screen.queryByText("Failed to load agent status"),
+    ).not.toBeInTheDocument();
+    expect(screen.getByText("Not running")).toBeInTheDocument();
+  });
+});

panel/src/app/(dashboard)/agents/[agentId]/page.tsx

@@ -65,8 +65,17 @@ export default function AgentDetailPage() {
   const router = useRouter();
   const agentId = params.agentId as string;
 
-  const { data: agent, isLoading, error, refetch } = useAgentStatus(agentId);
-  const { data: definition } = useAgentDefinition(agentId);
+  const {
+    data: agent,
+    isLoading: isStatusLoading,
+    error: statusError,
+    refetch,
+  } = useAgentStatus(agentId);
+  const {
+    data: definition,
+    isLoading: isDefinitionLoading,
+    error: definitionError,
+  } = useAgentDefinition(agentId);
 
   const { register, unregister } = usePageRefresh();
 
@@ -100,7 +109,13 @@ export default function AgentDetailPage() {
     }
   };
 
-  if (error) {
+  // Fatal only when the agent identity itself doesn't resolve (roster lookup
+  // failed) — a genuinely invalid id. A live-status error (agent not running)
+  // is a normal, expected state for a stopped agent and must not discard the
+  // DB-backed content below (activity panel, header) — see isAgentDown.
+  const isInvalidAgent = !!definitionError && !isDefinitionLoading;
+
+  if (isInvalidAgent) {
     return (
       <div className="space-y-6">
         <Button variant="ghost" onClick={() => router.back()}>
@@ -132,6 +147,11 @@ export default function AgentDetailPage() {
     );
   }
 
+  // Live status unreachable (stopped/unreachable agent, 404 from the
+  // orchestrator) but the agent identity is real — degrade in place instead
+  // of replacing the page.
+  const isAgentDown = !!statusError && !isStatusLoading;
+
   const isActive =
     agent &&
     ["running", "ready", "starting", "waiting_long"].includes(agent.state);
@@ -201,7 +221,7 @@ export default function AgentDetailPage() {
           History exists independent of live status, so render for any slug. */}
       <AgentActivityPanel agentSlug={agentId} agentUuid={definition?.uuid} />
 
-      {isLoading ? (
+      {isStatusLoading ? (
         <div className="grid gap-4 md:grid-cols-2 lg:grid-cols-4">
           {Array.from({ length: 4 }).map((_, i) => (
             <Card key={i}>
@@ -214,6 +234,29 @@ export default function AgentDetailPage() {
             </Card>
           ))}
         </div>
+      ) : isAgentDown ? (
+        <Card className="border-muted-foreground/30">
+          <CardContent className="pt-6">
+            <div className="flex items-center gap-2 text-muted-foreground">
+              <AlertTriangle className="h-5 w-5" />
+              <span>Not running</span>
+            </div>
+            <p className="text-muted-foreground mt-2">
+              Live status is unavailable — this agent isn&apos;t currently
+              active. Spawn it to see live state.
+            </p>
+            <SpawnAgentDialog
+              agentId={agentId}
+              agentName={displayName}
+              trigger={
+                <Button className="mt-4">
+                  <Play className="h-4 w-4 mr-2" />
+                  Spawn Agent
+                </Button>
+              }
+            />
+          </CardContent>
+        </Card>
       ) : agent ? (
         <>
           {/* Status Cards */}

panel/src/hooks/use-agents.ts

@@ -337,6 +337,9 @@ export function useAgentStatus(agentId: string) {
     queryFn: () => orchestratorApi.getAgentStatus(agentId),
     enabled: !!agentId,
     refetchInterval: 5000, // Refetch every 5 seconds
+    // A 404 (agent not running) is deterministic, not transient — retrying
+    // just delays settling into the degraded "not running" state.
+    retry: false,
   });
 }