feat(console-web): add bounded iframe keep-alive

- opt service and settings pages into document retention
- preserve iframe identity and local Solid state across navigation
- cap retained documents with deterministic LRU eviction
- deliver activate, deactivate, and dispose lifecycle messages
- reject commands emitted by inactive page documents
- expose page activity as a Solid accessor
- test retention, recreation, eviction, and invalid limits

crates/wasmeld-console/web/tests/frame-cache.test.mjs

@@ -0,0 +1,80 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { FrameCache } from "../src/host/frame-cache.ts";
+
+test("retains opted-in iframe identities across navigation", () => {
+  const cache = new FrameCache("services", {
+    maxKeepAliveEntries: 2,
+    shouldKeepAlive: (view) => view === "services" || view === "settings",
+  });
+  const services = cache.snapshot()[0];
+
+  const away = cache.activate("overview");
+  assert.deepEqual(
+    away.entries.map((entry) => entry.view),
+    ["services", "overview"],
+  );
+
+  const back = cache.activate("services");
+  assert.equal(back.activated, services);
+  assert.equal(back.activated.instance, services.instance);
+  assert.deepEqual(
+    back.removed.map((entry) => entry.view),
+    ["overview"],
+  );
+});
+
+test("recreates non-keep-alive documents after leaving them", () => {
+  const cache = new FrameCache("overview", {
+    maxKeepAliveEntries: 2,
+    shouldKeepAlive: () => false,
+  });
+  const firstInstance = cache.snapshot()[0].instance;
+
+  cache.activate("activity");
+  const transition = cache.activate("overview");
+
+  assert.notEqual(transition.activated.instance, firstInstance);
+  assert.deepEqual(
+    transition.removed.map((entry) => entry.view),
+    ["activity"],
+  );
+});
+
+test("evicts inactive keep-alive documents in LRU order", () => {
+  const cache = new FrameCache("services", {
+    maxKeepAliveEntries: 2,
+    shouldKeepAlive: () => true,
+  });
+  const servicesInstance = cache.snapshot()[0].instance;
+
+  cache.activate("settings");
+  const overflow = cache.activate("instances");
+
+  assert.deepEqual(
+    overflow.removed.map((entry) => entry.view),
+    ["services"],
+  );
+  assert.deepEqual(
+    overflow.entries.map((entry) => entry.view),
+    ["settings", "instances"],
+  );
+
+  const recreated = cache.activate("services");
+  assert.notEqual(recreated.activated.instance, servicesInstance);
+  assert.deepEqual(
+    recreated.removed.map((entry) => entry.view),
+    ["settings"],
+  );
+});
+
+test("rejects invalid keep-alive limits", () => {
+  assert.throws(
+    () =>
+      new FrameCache("overview", {
+        maxKeepAliveEntries: -1,
+        shouldKeepAlive: () => true,
+      }),
+    RangeError,
+  );
+});