Shell: single-instance tile entries, and a multiselect admin field

Two small pieces of contract for modules that offer several tiles from live
data:

- A `tiles()` entry may say `single: true`: at most one such tile per
  dashboard. The ＋ picker greys the entry out once it is placed ("Already on
  this dashboard") and `addTile` refuses a second — for a control surface
  that would only confuse in duplicate, a send box say.
- Admin config gains `multiselect`: several picks from one list, the same
  `options` / `optionsRoute` as `select`, one switch per option, stored as an
  array of values. A saved value the list no longer offers stays checked and
  marked rather than being dropped in silence. The wrapper is a <label>, so
  it is told to label nothing — otherwise a click anywhere would flip the
  first switch.

Both documented in the module guide.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/MODULE-GUIDE.md

@@ -104,7 +104,7 @@ the app); its settings are kept for a later reinstall.
 Both schemas map field names to specs:
 
 ```
-{ "type": "string" | "text" | "number" | "boolean" | "switch" | "select" | "color" | "password" | "endpoint",
+{ "type": "string" | "text" | "number" | "boolean" | "switch" | "select" | "multiselect" | "color" | "password" | "endpoint",
   "label": "Shown next to the field",
   "default": <value>,
   "group": "Section heading",                         // optional; see below
@@ -125,6 +125,11 @@ shown or enabled, off means hidden or disabled, and the label shouldn't say
 so twice.
 `color` renders a swatch picker and stores a `#rrggbb` string (give it a hex
 default; the tile applies it as a CSS custom property — see `pco-plan`).
+`multiselect` is several picks from one list — the same `options` /
+`optionsRoute` as `select`, rendered as one switch per option and stored as
+an array of values. A saved value the list no longer offers stays checked and
+marked, so nothing is dropped behind the admin's back (admin config only).
+
 `text` is a multi-line string — a `<textarea>` in the admin page, stored with
 its newlines; one item per line is the convention (the `slack` module's quick
 replies). Admin config only.
@@ -485,6 +490,9 @@ module.exports = {
   keep it fast (answer from state you already hold; don't fetch upstream on
   demand). A throw or a hang (>2 s) falls back to the classic single entry,
   so a dead upstream can't break the picker.
+- `single: true` on an entry allows at most one such tile per dashboard: the
+  picker greys the entry out once it is placed. Use it for a control surface
+  that would only confuse in duplicate — a send box, a master switch.
 - When the user adds an entry, its `settings` overlay your `instanceSchema`
   defaults in that tile's instance settings, the entry's `name` becomes the
   tile's title, and `moduleApi.variant` carries its `id`.

public/admin/admin.css

@@ -156,6 +156,12 @@ body { overflow: auto; }
 .endpoint-row .ep-host { flex: 1; min-width: 0; }
 .endpoint-row .ep-port { width: 92px; flex: none; }
 .endpoint-row .ep-sep { color: var(--muted); font-weight: 600; }
+/* several picks from a list (manifest type `multiselect`) */
+.field.multiselect-field { cursor: default; }
+.field.multiselect-field .multiselect { display: flex; flex-direction: column; gap: 6px; }
+.multiselect-row { display: flex; align-items: center; gap: 8px; cursor: pointer; }
+.multiselect-empty { color: var(--muted); font-size: 12px; }
+
 .module-form-empty { color: var(--muted); font-size: 12px; margin-top: 10px; }
 
 /* labeled config subsections (manifest field `group`) */

public/admin/admin.js

@@ -228,6 +228,73 @@ function fieldFor(key, spec, value, passwordSet, moduleId) {
     field.append(span, select);
     read = () => select.value;
     selectEl = select;
+  } else if (type === 'multiselect' && (Array.isArray(spec.options) || spec.optionsRoute)) {
+    // Several picks from one list — a switch per option, stored as an array
+    // of values. A saved value the list no longer offers stays checked and
+    // marked, so a channel the account has left isn't dropped in silence.
+    field.classList.add('multiselect-field');
+    // The wrapper is a <label>; with several controls inside, a click on the
+    // wrapper would activate the FIRST one. `for=""` makes it label nothing.
+    field.htmlFor = '';
+    const span = document.createElement('span');
+    span.textContent = label;
+    const list = document.createElement('div');
+    list.className = 'multiselect';
+    const chosen = new Set((Array.isArray(value) ? value : []).map(String).filter(Boolean));
+    const optValue = (opt) => String(typeof opt === 'object' ? opt.value : opt);
+    const fill = (options) => {
+      for (const input of list.querySelectorAll('input')) {
+        if (input.checked) chosen.add(input.value);
+        else chosen.delete(input.value);
+      }
+      list.innerHTML = '';
+      const missing = [...chosen].filter((v) => !options.some((opt) => optValue(opt) === v));
+      const all = [...options, ...missing.map((v) => ({ value: v, label: `${v} (saved — not listed now)` }))];
+      for (const opt of all) {
+        const row = document.createElement('div');
+        row.className = 'multiselect-row';
+        const toggle = document.createElement('span');
+        toggle.className = 'switch';
+        const input = document.createElement('input');
+        input.type = 'checkbox';
+        input.value = optValue(opt);
+        input.checked = chosen.has(input.value);
+        const track = document.createElement('span');
+        track.className = 'track';
+        toggle.append(input, track);
+        const text = document.createElement('span');
+        text.className = 'switch-label';
+        text.textContent = String(typeof opt === 'object' ? (opt.label ?? opt.value) : opt);
+        row.append(toggle, text);
+        row.addEventListener('click', (e) => {
+          if (e.target === input) return;           // the box toggles itself
+          input.checked = !input.checked;
+          input.dispatchEvent(new Event('change', { bubbles: true }));
+        });
+        list.appendChild(row);
+      }
+      if (!all.length) {
+        const none = document.createElement('div');
+        none.className = 'multiselect-empty';
+        none.textContent = 'Nothing to choose from yet.';
+        list.appendChild(none);
+      }
+    };
+    fill(Array.isArray(spec.options) ? spec.options : []);
+    if (spec.optionsRoute && moduleId) {
+      refetch = (query) => {
+        const qs = query && Object.keys(query).length ? `?${new URLSearchParams(query)}` : '';
+        return fetch(`/api/modules/${encodeURIComponent(moduleId)}${spec.optionsRoute}${qs}`)
+          .then((res) => (res.ok ? res.json() : null))
+          .then((body) => {
+            if (Array.isArray(body?.options)) fill(body.options);
+          })
+          .catch(() => { /* keep the static/saved options */ });
+      };
+      if (!spec.optionsDependsOn) refetch();
+    }
+    field.append(span, list);
+    read = () => [...list.querySelectorAll('input:checked')].map((input) => input.value);
   } else if (type === 'color') {
     // A swatch picker; the value is always a #rrggbb string.
     field.classList.add('color-field');

public/shell.js

@@ -108,9 +108,10 @@ function wireDropdown(btnId, menuId, rebuild) {
   return menu;
 }
 
-function menuItem(label, onClick, { sub = '', danger = false } = {}) {
+function menuItem(label, onClick, { sub = '', danger = false, disabled = false } = {}) {
   const item = document.createElement('button');
   item.className = 'menu-item' + (danger ? ' danger' : '');
+  item.disabled = disabled;
   const span = document.createElement('span');
   span.textContent = label;
   if (sub) {
@@ -706,6 +707,10 @@ function buildDivider(L, R, top, bottom) {
  */
 function addTile(moduleId, entry = null) {
   const man = registry.get(moduleId);
+  if (entry?.single && tiles.some((t) => t.module === moduleId && t.variant === String(entry.id))) {
+    toast(`${entry.name} is already on this dashboard`);
+    return;
+  }
   const defaultSize = entry?.defaultSize || man?.defaultSize;
   const size = {
     w: Math.max(1, Math.min(COLS, defaultSize?.w || 4)),
@@ -1316,10 +1321,13 @@ function renderAddMenu(menu) {
       title.textContent = man.name;
       menu.appendChild(title);
       for (const entry of entries) {
+        // An entry that allows one tile at most is offered greyed out once
+        // that tile exists — a second Send box would only confuse.
+        const placed = entry.single && tiles.some((t) => t.module === man.id && t.variant === String(entry.id));
         menu.appendChild(menuItem(entry.name, () => {
           menu.hidden = true;
           addTile(man.id, entry);
-        }, { sub: entry.description || '' }));
+        }, { sub: placed ? 'Already on this dashboard' : (entry.description || ''), disabled: placed }));
       }
     } else {
       menu.appendChild(menuItem(man.name, () => {

public/style.css

@@ -170,6 +170,7 @@ body.menu-hidden #topbar {
   margin-top: 2px;
   white-space: normal;
 }
+.menu-item[disabled] { opacity: 0.45; cursor: default; }
 .menu-item.danger { color: var(--danger); }
 .menu-note {
   padding: 8px 10px;

server.js

@@ -463,6 +463,8 @@ function sanitizeTileEntry(raw) {
     name: String(raw.name),
     description: raw.description ? String(raw.description) : '',
     settings: raw.settings && typeof raw.settings === 'object' ? raw.settings : {},
+    // at most one tile of this entry per dashboard (the picker greys it out)
+    single: raw.single === true,
   };
   for (const key of ['minSize', 'defaultSize']) {
     const size = raw[key];
@@ -1055,6 +1057,9 @@ function applyConfigPatch(id, patch) {
     }
     if (type === 'number') value = Number(value) || 0;
     else if (type === 'boolean' || type === 'switch') value = Boolean(value);
+    else if (type === 'multiselect') {
+      value = (Array.isArray(value) ? value : []).map((v) => String(v)).filter(Boolean);
+    }
     else if (type === 'endpoint') {
       const src = value && typeof value === 'object' ? value : {};
       value = {