perf(web): restore last known dashboard tiles

apps/web/src/App.test.tsx

@@ -2,7 +2,11 @@ import { renderToString } from "react-dom/server";
 import { describe, expect, test } from "vitest";
 import { genericDashboardFixture } from "@dimensionlab/dashboard-model/fixtures";
 import { dimensionLabDashboardFixture } from "$lib/dashboard-seed/dimensionlab";
-import { AppStateView, dashboardHydrationTiles } from "./App";
+import {
+  AppStateView,
+  dashboardHydrationTiles,
+  restoreDashboardTileSnapshots,
+} from "./App";
 
 describe("React app dashboard state view", () => {
   test("renders loading dashboard state", () => {
@@ -120,4 +124,39 @@ describe("React app dashboard state view", () => {
       ),
     );
   });
+
+  test("applies restored tile snapshots without marking them as loading", () => {
+    const restored = restoreDashboardTileSnapshots(
+      {
+        state: "ready",
+        document: dimensionLabDashboardFixture,
+        schemaVersion: "dashboard.v1",
+        currentRevisionId: "revision-a",
+      },
+      [
+        {
+          ageMs: 60_000,
+          response: {
+            state: "ready",
+            tile: { kind: "telemetry", id: "infra-ram" },
+            item: {
+              ...dimensionLabDashboardFixture.telemetry[0],
+              detail: "cached - stale 60s",
+              severity: "stale",
+            },
+          },
+        },
+      ],
+    );
+
+    expect(restored.restoredItemIds).toEqual(new Set(["telemetry:infra-ram"]));
+    if (restored.dashboard.state !== "ready") {
+      throw new Error("Expected dashboard to be ready");
+    }
+    expect(restored.dashboard.document.telemetry[0]).toMatchObject({
+      id: "infra-ram",
+      detail: "cached - stale 60s",
+      severity: "stale",
+    });
+  });
 });