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, 68 insertions, 0 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/chat-app-settings.js b/packages/meshbay-hub/src/meshbay_hub/static/chat-app-settings.js
new file mode 100644
index 0000000..68569b9
--- /dev/null
+++ b/packages/meshbay-hub/src/meshbay_hub/static/chat-app-settings.js
@@ -0,0 +1,68 @@
+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';
+
+/**
+ * Chat's operator settings.
+ *
+ * Every app's settings pane takes the same props (see `apps.js`): the group's
+ * roots and known folders, the node's current answers, a `saveDirectories`
+ * bound to this app, and the transport for anything the app alone needs. It
+ * owns its drafts and its own busy state, and the page renders it without
+ * naming it.
+ *
+ * The directory here is unlike every other app's. Videos, Music and Photos
+ * point at folders they *read*; this is where attachments get *written*, so it
+ * has to be on a read-write root. The picker greys out the rest rather than
+ * letting the node's refusal arrive after the fact.
+ */
+function ChatSettings({ roots, dirs, settings, saveDirectories, transport, signFn }) {
+  const { busy, msg, run } = useSaver();
+  const [directory, setDirectory] = useState(settings.chatDirectory || '');
+  const [linkPreview, setLinkPreview] = useState(settings.chatLinkPreview !== false);
+
+  // Re-seeded from the node's answer: another operator may be editing the
+  // same group, and their change arrives here as a prop.
+  useEffect(() => { setDirectory(settings.chatDirectory || ''); },
+            [settings.chatDirectory]);
+  useEffect(() => { setLinkPreview(settings.chatLinkPreview !== false); },
+            [settings.chatLinkPreview]);
+
+  const noWritable = !(roots || []).some((r) => r.writable);
+  const dirty = directory !== (settings.chatDirectory || '');
+
+  return html`
+    <div class="app-settings">
+      ${noWritable && html`
+        <p class="settings-hint">${t('settings_app.chat_no_writable_root')}</p>`}
+
+      <${FolderPickerField}
+        label=${t('settings_app.chat_directory_label')}
+        hint=${t('settings_app.chat_directory_hint')}
+        roots=${roots} dirs=${dirs}
+        mode="single" requireWritable=${true}
+        value=${directory} disabled=${busy || noWritable}
+        onChange=${setDirectory} />
+
+      <button class="btn btn-small btn-secondary" style="margin-top:4px"
+        disabled=${busy || !dirty}
+        onClick=${() => run(() => transport.setChatDirectory(directory, signFn))}>
+        ${busy ? t('settings_app.saving') : t('settings_app.save')}
+      </button>
+
+      <div class="settings-row" style="margin-top:12px">
+        <${ToggleSwitch} checked=${linkPreview} disabled=${busy}
+          onChange=${(v) => {
+            setLinkPreview(v);
+            run(() => transport.setChatLinkPreview(v, signFn));
+          }}
+          label=${t('settings_app.chat_link_preview_label')} />
+        <p class="settings-hint">${t('settings_app.chat_link_preview_hint')}</p>
+      </div>
+      ${msg && html`<p class="settings-hint">${msg}</p>`}
+    </div>
+  `;
+}
+
+export { ChatSettings };