feat(client): HelloWorld, the reference application

Every other test of the plugin architecture reads source for the *absence* of
app names. That proves nobody wrote a special case for Videos; it cannot prove
a genuinely new application works, because there was no new application.

This is one. It stores directories, appears as a tab, has a settings pane and
lists files, and the node has never heard its name outside a single allow-list
entry. Two files and one registry line, which is the claim
`docs/refactor-groups.md` §4.1 makes.

It ships hidden behind `?dev=1` (`dev: true` in the registry, the same opt-in
shape as transport.js's `?trace=1`). Registering it normally would put a toy
app in every operator's group; not registering it would prove nothing, since
registration is exactly what is claimed to be sufficient.

**Adding it found two places where the claim was nearly true rather than true,
and both are fixed by making the code less app-specific:**

`group-settings.js` fell back to the whole registry when a group had no
`enabled_apps` yet — which would have turned a hidden app on for everyone. It
asks `availableApps()` now.

`group-page.js` wrote out `videoDirectories` / `musicDirectories` /
`photoDirectories` by hand, so a fifth app would have needed that file edited.
It derives `<key>Directories` from the registry.

Neither was found by reading; both were found by adding the app, which is the
whole reason it exists.

Verified in a real Electron window as well as by the tests: hidden by default,
present with the flag, offered its own settings section, and listing exactly
the files under its configured folder and its subfolders — not the ones beside
it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011pvMdvLBG92jyhvD5pD6us

1 files changed, 16 insertions, 8 deletions

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 0a43724..6f41426 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/group-page.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/group-page.js
@@ -9,7 +9,7 @@ import {
   HUB, session, cacheGroupIndex, hubFetch, ensureFreshToken,
   _loadBundleKey, _loadRecoveryKey, _storeBundleKey,
 } from './hub-client.js';
-import { visibleApps } from './apps.js';
+import { APPS, visibleApps } from './apps.js';
 import { GroupName } from './group-name.js';
 import { FilePreview } from './files-app.js';
 import { VideoPlayer } from './video-player.js';
@@ -654,10 +654,19 @@ function GroupPage({ groupId, group, token, username, userId, userPrefs,
   // `group-settings.js` untouched — that page renders the panes without
   // knowing what any of them is for, which is what makes adding an app a
   // registry entry rather than an edit to the page.
+  // `<key>Directories` for every registered app, derived from the registry
+  // rather than written out. Naming them here would mean adding an app
+  // required editing this file, which is the one thing the plugin
+  // architecture is supposed to have removed — and the reference app
+  // (docs/refactor-groups.md §4.1) is what made the difference visible.
+  const perAppDirectories = useMemo(() => {
+    const out = {};
+    for (const app of APPS) out[`${app.key}Directories`] = appDirs(app.key);
+    return out;
+  }, [appDirs]);
+
   const appSettings = useMemo(() => ({
-    videoDirectories: appDirs('video'),
-    musicDirectories: appDirs('music'),
-    photoDirectories: appDirs('photo'),
+    ...perAppDirectories,
     chatDirectory,
     chatLinkPreview,
     tmdbEnabled: tmdbConfig ? tmdbConfig.enabled !== false : true,
@@ -665,7 +674,8 @@ function GroupPage({ groupId, group, token, username, userId, userPrefs,
     tmdbTokenCustomized: Boolean(tmdbConfig && tmdbConfig.tokenCustomized),
     musicbrainzEnabled: musicbrainzConfig
       ? musicbrainzConfig.enabled !== false : true,
-  }), [appDirs, chatDirectory, chatLinkPreview, tmdbConfig, musicbrainzConfig]);
+  }), [perAppDirectories, chatDirectory, chatLinkPreview, tmdbConfig,
+       musicbrainzConfig]);
 
   const commonProps = {
     groupId, transportRef, gekRef, status, username,
@@ -676,9 +686,7 @@ function GroupPage({ groupId, group, token, username, userId, userPrefs,
     // Plural everywhere: Videos and Music read a list now, and Photos always
     // did. The scalar `videoRoot`/`audioRoot` shapes survive only on the wire,
     // for a node that speaks MNP 1.0 — nothing in the client carries them.
-    videoDirectories: appDirs('video'),
-    musicDirectories: appDirs('music'),
-    photoDirectories: appDirs('photo'),
+    ...perAppDirectories,
     tmdbConfig,
     musicbrainzConfig, onPlayQueue,
   };