composer-ui

name: composer-ui description: Use when building or styling plugin UI with Composer's design system — the @dxos/react-ui* packages. Covers theme tokens, primitives (Panel/Card/List/Input/Button/Icon), the standard container layout (Panel + ScrollArea), lists/pickers/stacks, schema-driven forms, toolbar/menu wiring, reactivity (useObject), attention/density, translations, and storybook setup. The UI adjunct to the composer-plugins skill; consult it whenever you write a container/component, reach for a Tailwind color class, build a toolbar, render a form or list, or add a story.

Composer UI

How to consume Composer's design system (@dxos/react-ui*) from a plugin. This is the UI adjunct to [[composer-plugins]] (which owns plugin structure: capabilities, surfaces, schema, operations) and [[composite-components]] (which owns authoring new @dxos/react-ui primitives). When you're laying out a container, picking a color class, wiring a toolbar, or writing a story, the rules live here.

Golden rule: the design system already has a primitive, a token, or a layout for what you need. Reaching for a raw <div> with custom classes, a native <input>, or a guessed color token is almost always a sign you missed an existing piece. Find it (grep an existing themed component) before inventing.

Package family

Import from the most specific package. Common ones:

Many more exist (-card, -chat, -thread, -pickers, -search, -syntax-highlighter, …). When you need a domain widget, check for a react-ui-<domain> package before building one.

Theme tokens

Color/spacing tokens are plain Tailwind classes generated from CSS custom properties. The source of truth is packages/ui/ui-theme/src/css/theme/semantic.css and the per-component files under packages/ui/ui-theme/src/css/components/.

The rule: every --color-<name> custom property yields the utilities bg-<name>, text-<name>, border-<name>. So --color-modal-surface → bg-modal-surface. To find a valid token, grep semantic.css for --color-, or copy classes from an existing themed component — never guess a name. Invented tokens (bg-input, text-primary) aren't in the theme and render wrong (e.g. white-on-white in dark mode), which is the kind of bug that's invisible until someone toggles the theme.

Verified common tokens (kebab-case is current; legacy camelCase like bg-modalSurface / text-baseText is being phased out — prefer the kebab forms):

• Surfaces: bg-base-surface, bg-card-surface, bg-modal-surface, bg-toolbar-surface, bg-sidebar-surface, bg-deck-surface, bg-group-surface, bg-input-surface, bg-hover-surface, bg-attention-surface, bg-accent-bg (+ -hover).
• Text: text-base-fg (body), text-description (muted), text-subdued (dimmest), text-placeholder, text-accent-text.
• Borders: border-separator, border-subdued-separator, border-primary-separator, border-active-separator, border-focus-ring.

Themed primitives accept overrides via a classNames prop (string or array) — never className. Pass functional layout hints (p-4, space-y-4, flex, @container queries) freely; pass color/size through tokens. If you're writing more than a layout hint by hand, you're probably missing a primitive.

Icons

Icons are Phosphor sprite references named ph--<icon>--<weight> (weights: regular, bold, fill, light, duotone, thin). Use the Icon primitive or any primitive that takes an icon prop:

import { Icon } from '@dxos/react-ui';
<Icon icon='ph--plus--regular' size={5} />;

size is a numeric Size (Tailwind scale), or inherit from the --dx-icon-size CSS var. See packages/ui/react-ui/src/components/Icon/Icon.tsx.

Containers: Panel + ScrollArea

Panel.* (packages/ui/react-ui/src/components/Panel/Panel.tsx) is the container shell — a CSS grid with rows auto 1fr auto mapped to the toolbar / content / statusbar areas, so the content row absorbs the slack and the toolbar/statusbar hug their content. The canonical article shape:

<Panel.Root role={role}>
  <Panel.Toolbar>{/* Menu.Root toolbar — see below */}</Panel.Toolbar>
  <Panel.Content asChild>
    <ScrollArea.Root orientation='vertical'>
      <ScrollArea.Viewport>{/* List / Stack / Form, or ad-hoc content */}</ScrollArea.Viewport>
    </ScrollArea.Root>
  </Panel.Content>
</Panel.Root>

Parts: Panel.Root / Panel.Toolbar / Panel.Content / Panel.Statusbar. Add Panel.Statusbar (takes a size) only when the surface needs a persistent bottom status row — most articles don't.

role: Panel.Root defaults role to none. Only pass a role that the surface itself receives (the article/section/companion role threaded in via AppSurface.*Props) — don't invent ARIA roles to hang behaviour on.

asChild + composable. Every Panel.* part is slottable, so asChild makes the part become its single child instead of rendering its own <div>. Use asChild whenever the child is itself composable (e.g. ScrollArea.Root): one fewer DOM node, and the height chain passes straight through. ScrollArea provides the themed scrollbar and the height chain that lets content scroll — content that should scroll goes in ScrollArea.Viewport inside Panel.Content asChild.

Let components own their spacing. Form, List, and Stack each control their own padding and spacing — don't wrap them in a padded viewport or sprinkle p-*/space-* around them; that double-pads and fights their internal rhythm. Reserve hand-written layout hints (p-4 space-y-4, @container queries) on ScrollArea.Viewport for ad-hoc free-form content that has no owning component. Anything beyond a layout hint means you're probably missing a primitive — clear it with the user first.

Never introduce a wrapper <div> for styling. Wrappers break the height chain that ScrollArea relies on (a wrapper around an input once silently disabled scrolling). If a context-provider component (like Input.Root, which renders no DOM) has nowhere to hang a class, rely on parent-level layout rules rather than wrapping — and if there's genuinely no path without a wrapper, discuss it first.

See: plugin-chess/src/containers/ChessArticle/, plugin-sample/src/containers/.

Lists, pickers, and stacks

Pick the collection primitive by decision order — don't hand-roll a list of mapped <div>s:

1. Need a picker / combobox (choose from a set, typeahead)? Check for an existing one first — Picker / Combobox / Listbox in @dxos/react-ui-list, or a domain widget like SearchList (@dxos/react-ui-search). Reuse before building.
2. A simple flat or tree list? Use @dxos/react-ui-list — List, RowList, Tree, Accordion.
3. A reorderable / resizable / tiled collection of surfaces? Use the Stack from @dxos/react-ui-mosaic (MosaicStack / MosaicVirtualStack, with MosaicStackTileComponent tiles).

Do NOT use @dxos/react-ui-stack — it is deprecated. (Some plugins still import it; don't copy them.) The live Stack is the Mosaic one.

dx-current / dx-selected are automatic. List and Stack drive current-item and selection state themselves (via react-tabster keyboard navigation) — you don't set those classes or wire focus by hand. Like Form, both own their own padding and spacing, so drop them straight into a ScrollArea.Viewport without a padded wrapper.

Toolbar / menu wiring

Container toolbars are always built from menu actions, never bare Toolbar.IconButton chains. Compose actions with MenuBuilder inside an Atom, thread them through useMenuActions, and render with Menu.Root — passing attendableId so attention-driven contributions (graph actions, plugin extensions, keyboard shortcuts) target the right surface. Skipping this breaks plugin composition.

const actionsAtom = useMemo(
  () =>
    Atom.make(
      (): ActionGraphProps =>
        MenuBuilder.make()
          .action(
            'add',
            { label: ['add.label', { ns: meta.id }], icon: 'ph--plus--regular', disposition: 'toolbar' },
            handleAdd,
          )
          .build(),
    ),
  [handleAdd],
);
const menuActions = useMenuActions(actionsAtom);

return (
  <Panel.Toolbar>
    <Menu.Root {...menuActions} attendableId={attendableId}>
      <Menu.Toolbar />
    </Menu.Root>
  </Panel.Toolbar>
);

Encode dynamic state (disabled, busy/idle icon swap) inside the action properties and list that state in the useMemo deps — the atom rebuilds and the toolbar updates. Always thread attendableId from AppSurface.ObjectArticleProps; don't underscore it as unused.

See: plugin-sample/src/containers/SampleArticle.tsx.

Reactivity

When an ECHO object is passed into a component as a prop and the component must re-render on changes to it, wrap it with useObject and read from the returned snapshot. A surface receiving an ECHO subject (e.g. via AppSurface.ObjectArticleProps<T>) MUST do this — without it, mutations to nested arrays/structs (e.g. Obj.update(obj, (m) => (m.images = [...]))) don't trigger a re-render until you navigate away and back: the prop reference stays stable, and the subscription lives inside useObject.

const [gallery] = useObject(subject);
// reads (gallery.images) re-render reactively;
// writes still go through the original subject:
const handleDelete = (index: number) =>
  Obj.update(subject, (obj) => {
    const mutable = obj as Obj.Mutable<Gallery.Gallery>;
    mutable.images = (mutable.images ?? []).filter((_, idx) => idx !== index);
  });

The snapshot type is narrow — cast as needed (obj as Obj.Mutable<T> inside Obj.update, or as T to read fields not surfaced on Snapshot<T>). For collections of objects use the reactive useQuery rather than holding a plain array. (Pure presentational components that just receive scalar props don't need any of this — keep useObject at the container boundary where the ECHO object enters.)

Forms

Never hand-roll native <input> / <textarea> / <select> in a plugin — they don't inherit the theme (a bare textarea is a white box in dark mode) and bypass validation. Edit objects with the schema-driven Form from @dxos/react-ui-form, which renders themed inputs from the Effect Schema (strings, numbers, booleans, enums via Schema.Literal/Format, nested Schema.Struct, Schema.Array, Schema.Record).

Form is composed — Form.Root renders nothing on its own. The fields come from Form.FieldSet (or Form.Layout), nested inside the standard Radix wrapper pair: Form.Viewport (outer) → Form.Content (inner), which own scroll and padding (so, like List/Stack, don't pad them yourself):

<Form.Root schema={Type.getSchema(Foo)} values={obj} autoSave onSave={handleSave}>
  <Form.Viewport>
    <Form.Content>
      <Form.Section label='…' description='…' /> {/* optional grouping */}
      <Form.FieldSet /> {/* fields, generated from the schema */}
      <Form.Actions /> {/* Save/Cancel — omit when autoSave */}
    </Form.Content>
  </Form.Viewport>
</Form.Root>

• Form.FieldSet is driven entirely by the schema and its annotations — fields, order, labels, visibility. Hide a field with FormInputAnnotation.set(false); there's no manual field markup.
• Form.Layout template={…} is the alternative to FieldSet: a custom layout DSL for arranging fields (grouping, columns, ordering) when the default schema order isn't enough.

Save model — the form never mutates values; the parent applies the change. Pick a mode:

• autoSave + onSave — on blur, if valid and changed, calls onSave(values, { changed, isValid }). This is the usual ECHO-object pattern: onSave writes back via Obj.update. No Form.Actions needed.
• onSave without autoSave — onSave fires only on explicit submit (Form.Actions / Form.Submit, gated by canSave). Use when you want a deliberate Save/Cancel.
• onValuesChanged — controlled: fires on every change with merged values + meta; the parent holds the state. Pair with values.

values is the controlled current value; defaultValues seeds an uncontrolled form that keeps its own internal state. To edit an opaque document (e.g. a stored JSON Schema), model it with typed sub-schemas and render those rather than dropping to a <textarea>. For a one-off input not backed by a schema object, use Input.Root + Input.TextInput.

Custom field renderers. When a field needs an editor the schema can't express, supply a FormFieldComponent (an FC<FormFieldComponentProps> — label, readonly, and value/onChange wiring) — never a native element. Choose how to register it by when you know which fields need it:

• fieldMap: Record<jsonPath, FormFieldComponent> — static, when you know the property paths ahead of time. Override the renderer for specific named fields.
• fieldProvider: (props) => FormFieldComponent | undefined — dynamic, when you must decide at runtime (e.g. by type or annotation rather than exact path). Preferred for plugin-specific input surfaces.

See: packages/ui/react-ui-form/src/components/Form/Form.stories.tsx (a dedicated canonical custom-field example is planned — tracked separately).

Cards: 3-slot subgrid

Card.Header and Card.Row are 3-slot subgrids (grid-cols-subgrid: leading icon · 1fr content · trailing action), placed by child order. A lone <Card.Title> lands in the narrow leading slot and gets clamped (a title renders as "20…"). Put real content in the centre slot — bracket it with icon slots or wrap it in one element occupying slot 2:

<Card.Header>
  <Card.IconBlock /> {/* slot 1 (icon) */}
  <div className='flex flex-col gap-0.5 min-w-0'>
    {' '}
    {/* slot 2 (1fr content) */}
    <Card.Title classNames='line-clamp-2'>{title}</Card.Title>
    {price && <span className='text-sm text-description'>{price}</span>}
  </div>
  <Card.IconBlock /> {/* slot 3 (action) */}
</Card.Header>

A card used as the child of Focus.Item asChild (or any Radix Slot/asChild) must be composable — a single element that forwards ref and spreads injected props, or the Slot's ref/handlers silently drop and current/keyboard/click wiring never attaches. Make presentational cards forwardRef and spread:

export const FooCard = forwardRef<HTMLDivElement, FooCardProps>(({ subject, current, classNames, ...props }, ref) => (
  <Card.Root ref={ref} classNames={['dx-hover', current && 'dx-current', classNames]} {...props}>
    …
  </Card.Root>
));

For authoring brand-new composite primitives (Radix-style Foo.Root/Foo.Content with slottable() / composableProps), see [[composite-components]].

Attention & density

• Attention (@dxos/react-ui-attention): surfaces carry an attendableId; focusing one registers it so contributions target it and AttentionGlyph reflects focus. As a plugin author you mostly just thread attendableId into Menu.Root (above) and let the shell handle the rest.
• Density (DensityProvider / useDensity, values xs|sm|md|lg): scales spacing and hit-areas. Primitives read it automatically; wrap a region in <DensityProvider density='…'> only to override.

Translations (i18n)

Use useTranslation(meta.id) for plugin-scoped strings and reference labels as ['key', { ns: meta.id }] (as in the menu action above). Resources are keyed by language → namespace → key, declared in the plugin's translations.ts and contributed via addTranslationsModule. See [[composer-plugins]] for registration.

Storybook

Every major component and container gets a .stories.tsx beside it — the user reviews agent-built UI primarily through storybook, so a missing story means the component effectively doesn't exist for review. Start with a very basic story for each (mount it with realistic props); add variants later. Mount it with these decorators (import from @dxos/react-ui/testing):

import { type Meta, type StoryObj } from '@storybook/react-vite';
import { withLayout, withTheme } from '@dxos/react-ui/testing';
import { translations } from '#translations';

const meta = {
  title: 'plugins/plugin-foo/FooView',
  component: FooView,
  decorators: [withTheme(), withLayout({ layout: 'centered' })],
  parameters: { translations },
} satisfies Meta<typeof FooView>;

export default meta;
type Story = StoryObj<typeof meta>;
export const Default: Story = {
  args: {
    /* realistic props */
  },
};

Two things break silently if omitted:

• withTheme() must be CALLED with parens — it's a factory returning the decorator. Passing withTheme (no parens) passes the factory itself and theme/types break.
• parameters: { translations } (from #translations) is required for useTranslation labels to resolve. Without it, triggers show the raw key (foo.add.label) instead of the translated text — which looks like a bug in a screenshot but isn't.

For a container with complex data behavior (loading, mutation, multi-step interaction), add a Storybook play function that drives and asserts the interaction — a basic static story isn't enough to catch regressions in behaviour. Keep the basic story too; play is the second step, not a replacement.

Capability hooks (useCapability, useAppGraph, useOperationInvoker) throw in storybook (no PluginManager). Keep those in containers/ and take resolved values as props in components/ so the component is storybook-mountable. See [[composer-plugins]] ("Container vs Component").

See: plugin-sample/src/containers/SampleArticle.stories.tsx, plugin-chess/src/components/Chessboard/Chessboard.stories.tsx.

Verifying a story in a worktree

preview_start serves storybook from the main repo, so it won't include stories that exist only in a worktree. To verify worktree UI, run storybook from the worktree on a free port and drive it with Playwright:

moon run storybook-react:serve -- --port 9014 --no-open --ci

Find story ids via curl -s localhost:9014/index.json, navigate to http://localhost:9014/iframe.html?id=<story-id>&viewMode=story. Screenshots go to temp/ (gitignored), never the repo root. If a story renders empty with "Invalid hook call" / "Cannot read … 'useEffect'" / 504 "Outdated Optimize Dep", that's Vite dep-optimizer churn (dual React), not your code — kill storybook, rm -rf node_modules/.cache/storybook, restart. Clean up the port and cache when done.

Checklist

• Layout from Panel.* + ScrollArea.*; no wrapper <div>s for styling; asChild when the child is composable.
• Let Form/List/Stack own their padding/spacing — don't double-pad them.
• Collections: existing picker/combobox → react-ui-list list → Mosaic Stack. Never @dxos/react-ui-stack (deprecated).
• Colors from verified tokens (grep semantic.css / copy a component); no invented tokens, no className.
• Toolbars via MenuBuilder + useMenuActions + Menu.Root with attendableId.
• Object editing via composed Form (Viewport/Content/FieldSet) + schema; no native inputs; form never mutates values.
• ECHO object passed into a component → wrap with useObject at the container boundary.
• Icons as ph--<icon>--<weight>.
• Every major component/container has a basic .stories.tsx with withTheme() (parens) + parameters: { translations }; add a play function for complex data behaviour.
• Authoring a new Foo.Root/Foo.Content primitive → [[composite-components]]; plugin wiring/surfaces → [[composer-plugins]].