fix(app): show late archive failures after the sidebar unmounts

An archive keeps the toast API it started with. Unmounting the sidebar (focus
mode, a layout change, a plugin view) left the ref saying it was visible, so a
failure arriving afterwards went to the removed host and the user saw nothing.

packages/app/src/components/sidebar/sidebar-toast-region.test.tsx

@@ -0,0 +1,71 @@
+// @vitest-environment jsdom
+
+import { render } from "@testing-library/react";
+import { SafeAreaProvider } from "react-native-safe-area-context";
+import { describe, expect, it, vi } from "vitest";
+import type { ToastApi } from "@/components/toast-host";
+import { ToastApiProvider, useToast } from "@/contexts/toast-context";
+import { SidebarToastRegion } from "./sidebar-toast-region";
+
+const safeAreaMetrics = {
+  frame: { x: 0, y: 0, width: 800, height: 600 },
+  insets: { top: 0, left: 0, right: 0, bottom: 0 },
+};
+
+function createFakeToast(): ToastApi {
+  return { show: vi.fn(() => () => {}), copied: vi.fn(), error: vi.fn() };
+}
+
+function renderRegion(active: boolean) {
+  const appToast = createFakeToast();
+  let regionToast: ToastApi | null = null;
+  function CaptureToast() {
+    regionToast = useToast();
+    return null;
+  }
+  const tree = (isActive: boolean) => (
+    <SafeAreaProvider initialMetrics={safeAreaMetrics}>
+      <ToastApiProvider api={appToast}>
+        <SidebarToastRegion active={isActive}>
+          <CaptureToast />
+        </SidebarToastRegion>
+      </ToastApiProvider>
+    </SafeAreaProvider>
+  );
+  const view = render(tree(active));
+  return {
+    appToast,
+    toast: () => regionToast as unknown as ToastApi,
+    setActive: (next: boolean) => view.rerender(tree(next)),
+    unmount: view.unmount,
+  };
+}
+
+describe("SidebarToastRegion", () => {
+  it("keeps toasts in the sidebar while it is visible", () => {
+    const { appToast, toast } = renderRegion(true);
+
+    toast().error("Archive failed");
+
+    expect(appToast.error).not.toHaveBeenCalled();
+  });
+
+  it("sends toasts to the app while the sidebar is hidden", () => {
+    const { appToast, toast, setActive } = renderRegion(true);
+
+    setActive(false);
+    toast().error("Archive failed");
+
+    expect(appToast.error).toHaveBeenCalledWith("Archive failed");
+  });
+
+  it("sends a late failure to the app after the sidebar unmounts", () => {
+    const { appToast, toast, unmount } = renderRegion(true);
+    const savedToast = toast();
+
+    unmount();
+    savedToast.error("Archive failed");
+
+    expect(appToast.error).toHaveBeenCalledWith("Archive failed");
+  });
+});

packages/app/src/components/sidebar/sidebar-toast-region.tsx

@@ -18,8 +18,12 @@ export function SidebarToastRegion({ active, children }: { active: boolean; chil
 
   useEffect(() => {
     activeRef.current = active;
-    // A toast must not outlive its visibility: its dismissal is what ends an archive's undo.
-    return active ? dismiss : undefined;
+    return () => {
+      // An archive holds on to this API, so a failure that lands later needs a host on screen.
+      activeRef.current = false;
+      // A toast must not outlive its visibility: its dismissal is what ends an archive's undo.
+      dismiss();
+    };
   }, [active, dismiss]);
 
   const api = useMemo<ToastApi>(() => {