feat(client): Phase 2 — per-app settings panes, folder tree, multi-directory

Each app's settings were inlined in `group-settings.js` — TMDB, MusicBrainz,
and one folder picker per app, each with its own draft state and save handler
saying the same thing about a different key. They are one file per app now,
reached through the `apps.js` registry, and the page that renders them names no
application at all: adding one is a registry entry and a settings file.

The line between the two is what makes that true. What every app has — folders
— the page does generically, through one `saveDirectories` bound to the app.
What one app alone has, its pane does itself with the transport it is handed.
An app that only needs directories touches neither `group-settings.js` nor
`group-page.js`, which is `test_app_settings_plugin.py`'s subject.

`settings-ui.js` exists because a pane importing the page that renders it is a
cycle, and ES modules answer that with a temporal-dead-zone ReferenceError at
first render — a component that silently does not appear, the fault already
recorded in CLAUDE.md about hook ordering.

The flat depth-indented `<select>` of every folder in the library becomes a
modal tree. It asks the node for nothing: the tree is derived from paths the
client already holds, so it shows exactly what the group's index contains and
adds no folder-browsing protocol. For Chat's attachment folder — the one
directory that is written to rather than read — read-only roots are greyed
out, so the node's refusal arrives before the operator picks rather than when
somebody sends a file.

Videos and Music take a list of folders. A library on two drives could not be
described before; the only recourse was pointing the app at a parent containing
both, which pulls in everything else under it. The scalar shapes survive on the
wire alone, for a node speaking MNP 1.0, and the client reads them as a
one-element list.

Two things the tests caught that I would not have:

`test_asset_versioning` — six new modules were missing from `_ASSETS`. Reached
through the registry rather than imported by name, they are exactly the files
nothing else would notice changing, and a stale one is served from cache with
no version bump.

And `node --check foo.js` does **not** reliably report a module syntax error:
it accepted `${/* ... */''}` — htm template syntax pasted into a plain object
literal — and reported success. A `.mjs` copy forces the module parser and
reports it. The suite had no syntax check at all, which is how that reached a
file; `test_spa_syntax.py` does it for every module now, and pins that the
loose path is not what it uses.

Suite: 12 failures, all pre-existing.

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

1 files changed, 61 insertions, 0 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/music-app-settings.js b/packages/meshbay-hub/src/meshbay_hub/static/music-app-settings.js
new file mode 100644
index 0000000..01174b1
--- /dev/null
+++ b/packages/meshbay-hub/src/meshbay_hub/static/music-app-settings.js
@@ -0,0 +1,61 @@
+import { html, useState, useEffect } from './vendor/htm-preact.js';
+import { t } from './i18n.js';
+import { ToggleSwitch, useSaver } from './settings-ui.js';
+import { FolderPickerField } from './folder-tree.js';
+
+/**
+ * The Music app's operator settings.
+ *
+ * Same shape as Videos, minus a credential: MusicBrainz's read endpoints need
+ * no API key, only a descriptive User-Agent, and that is one operator identity
+ * held node-wide rather than a per-group setting (docs/musicbay.md §3.2).
+ *
+ * Several folders, for the same reason Videos has several: a music library
+ * that lives on two drives had no way to say so.
+ */
+function MusicSettings({ roots, dirs, settings, saveDirectories, transport, signFn }) {
+  const { busy, msg, run } = useSaver();
+  const [directories, setDirectories] = useState(settings.musicDirectories || []);
+  const [mbEnabled, setMbEnabled] = useState(settings.musicbrainzEnabled !== false);
+
+  useEffect(() => {
+    setDirectories(settings.musicDirectories || []);
+  }, [settings.musicDirectories]);
+  useEffect(() => {
+    setMbEnabled(settings.musicbrainzEnabled !== false);
+  }, [settings.musicbrainzEnabled]);
+
+  const current = settings.musicDirectories || [];
+  const dirsDirty = directories.length !== current.length
+    || directories.some((d, i) => d !== current[i]);
+
+  return html`
+    <div class="app-settings">
+      <${FolderPickerField}
+        label=${t('settings_app.music_directories_label')}
+        hint=${t('settings_app.music_directories_hint')}
+        roots=${roots} dirs=${dirs} mode="multi"
+        value=${directories} disabled=${busy}
+        onChange=${setDirectories} />
+
+      <button class="btn btn-small btn-secondary" style="margin-top:4px"
+        disabled=${busy || !dirsDirty}
+        onClick=${() => run(() => saveDirectories(directories))}>
+        ${busy ? t('settings_app.saving') : t('settings_app.save')}
+      </button>
+
+      <h4 class="app-settings-sub">${t('settings_node.musicbrainz_title')}</h4>
+      <p class="settings-hint">${t('settings_node.musicbrainz_hint')}</p>
+      <div class="settings-row">
+        <${ToggleSwitch} checked=${mbEnabled} disabled=${busy}
+          onChange=${(v) => { setMbEnabled(v);
+                              run(() => transport.setMusicbrainzEnabled(v, signFn)); }}
+          label=${mbEnabled ? t('settings_node.musicbrainz_enabled')
+                            : t('settings_node.musicbrainz_disabled')} />
+      </div>
+      ${msg && html`<p class="settings-hint">${msg}</p>`}
+    </div>
+  `;
+}
+
+export { MusicSettings };