feat(client): fetch the media apps, the player, settings and search on first use

apps.js registers Videos, Music, Photos and every settings pane through
lazy.js; the group page does the same for the video player and the
settings panel, and the shell for the search page. The first download
goes from 49 modules / 386 KB gzip to 37 / 289 KB; opening Music now
fetches music-app.js and media-tiles.js and nothing of Videos.
test_first_load_is_lean holds the eager graph; test_spa_imports checks
that every on-demand load names an export that exists.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

4 files changed, 69 insertions, 12 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/app.js b/packages/meshbay-hub/src/meshbay_hub/static/app.js
index 856a774..6b20a63 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/app.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/app.js
@@ -20,7 +20,7 @@ import {
 } from './hub-client.js';
 import { startIdleWatch, markActive } from './idle.js';
 import { GroupPage } from './group-page.js';
-import { SearchPage } from './search-page.js';
+import { lazy } from './lazy.js';
 import { ConnectionPool } from './connection-pool.js';
 import { MusicPlayerBar } from './music-player.js';
 import { NameModal } from './playlist-menu.js';
@@ -623,6 +623,13 @@ function SetupWelcome({ onDismiss }) {
   </div>`;
 }
 
+// ── Lazy-loaded Search page ──────────────────────────────────────────────────
+//
+// It renders every app's results, so importing it here would bring every app
+// into the first download.
+const SearchPage = lazy(() => import('./search-page.js'), 'SearchPage',
+  html`<div class="page-content"><p class="page-message"><span class="spinner"></span></p></div>`);
+
 // ── Lazy-loaded Create Group page ────────────────────────────────────────────
 
 let _CreateGroupPage = null;
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/apps.js b/packages/meshbay-hub/src/meshbay_hub/static/apps.js
index eec2158..8ae4db4 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/apps.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/apps.js
@@ -1,14 +1,19 @@
 import { ChatPanel } from './chat-app.js';
 import { FilesPanel } from './files-app.js';
-import { VideoApp } from './video-app.js';
-import { MusicApp } from './music-app.js';
-import { PhotosApp } from './photos-app.js';
-import { ChatSettings } from './chat-app-settings.js';
-import { VideoSettings } from './video-app-settings.js';
-import { MusicSettings } from './music-app-settings.js';
-import { PhotoSettings } from './photos-app-settings.js';
-import { HelloWorldApp } from './helloworld-app.js';
-import { HelloWorldSettings } from './helloworld-app-settings.js';
+import { lazy } from './lazy.js';
+
+// Chat and Files open with the group; every other app, and every settings
+// pane, is fetched the first time it is shown (lazy.js) — a member who only
+// chats never downloads the Videos app.
+const VideoApp = lazy(() => import('./video-app.js'), 'VideoApp');
+const MusicApp = lazy(() => import('./music-app.js'), 'MusicApp');
+const PhotosApp = lazy(() => import('./photos-app.js'), 'PhotosApp');
+const ChatSettings = lazy(() => import('./chat-app-settings.js'), 'ChatSettings');
+const VideoSettings = lazy(() => import('./video-app-settings.js'), 'VideoSettings');
+const MusicSettings = lazy(() => import('./music-app-settings.js'), 'MusicSettings');
+const PhotoSettings = lazy(() => import('./photos-app-settings.js'), 'PhotoSettings');
+const HelloWorldApp = lazy(() => import('./helloworld-app.js'), 'HelloWorldApp');
+const HelloWorldSettings = lazy(() => import('./helloworld-app-settings.js'), 'HelloWorldSettings');
 
 /**
  * Whether apps marked `dev` are shown. Opt in once with `?dev=1`, off with
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/group-page.js b/packages/meshbay-hub/src/meshbay_hub/static/group-page.js
index f0a98e4..2ee6e05 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/group-page.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/group-page.js
@@ -13,8 +13,12 @@ import { APPS, visibleApps } from './apps.js';
 import { GroupName } from './group-name.js';
 import { useStickyBand } from './sticky.js';
 import { FilePreview } from './files-app.js';
-import { VideoPlayer } from './video-player.js';
-import { GroupSettingsPanel } from './group-settings.js';
+import { lazy } from './lazy.js';
+
+// Fetched the first time a video is played / the Settings tab is opened.
+const VideoPlayer = lazy(() => import('./video-player.js'), 'VideoPlayer',
+  html`<div class="video-overlay"><p class="page-message"><span class="spinner"></span></p></div>`);
+const GroupSettingsPanel = lazy(() => import('./group-settings.js'), 'GroupSettingsPanel');
 import { reportIndexPush } from './index-dock.js';
 import { clearPending, nodePkFromLink, pendingFor } from './invite-link.js';
 
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/lazy.js b/packages/meshbay-hub/src/meshbay_hub/static/lazy.js
new file mode 100644
index 0000000..30a564c
--- /dev/null
+++ b/packages/meshbay-hub/src/meshbay_hub/static/lazy.js
@@ -0,0 +1,41 @@
+// A component whose code is fetched the first time it is shown.
+//
+// Every static `import` reachable from app.js is downloaded before anything
+// renders, whether or not the visitor ever opens it: the Videos app, the video
+// player and the search page used to cost a member who only chats. Wrapping a
+// component here moves its module out of that first download and into the
+// moment it is needed; once loaded it is the component itself, rendered with
+// the same props, and every later mount is immediate.
+//
+// A failed fetch (a network drop on a phone) is not remembered: the next time
+// the component is shown it asks again, rather than failing for the session.
+
+import { html, useState, useEffect } from './vendor/htm-preact.js';
+
+const SPINNER = html`<p class="page-message"><span class="spinner"></span></p>`;
+
+function lazy(load, name, placeholder = SPINNER) {
+  let Loaded = null;
+  let pending = null;
+
+  function Lazy(props) {
+    const [, setReady] = useState(Loaded !== null);
+    useEffect(() => {
+      if (Loaded) return undefined;
+      let alive = true;
+      if (!pending) {
+        pending = load().then(
+          (m) => { Loaded = m[name]; },
+          (e) => { pending = null; throw e; });
+      }
+      pending.then(() => { if (alive) setReady(true); }, () => {});
+      return () => { alive = false; };
+    }, []);
+    if (!Loaded) return placeholder;
+    return html`<${Loaded} ...${props} />`;
+  }
+  Lazy.displayName = `Lazy(${name})`;
+  return Lazy;
+}
+
+export { lazy };