feat(select): invalid state + ItemDescription + defaultValue + visual fixes

Audit-driven improvements to Select:

- morfo APG URL fixed (combobox → listbox; Select is a collapsible-listbox
  per ARIA APG, not a text-input combobox).
- `invalid` prop added to soma + morfo data-invalid/aria-invalid on Provider
  and Trigger. Eidos applies risk-border + tinted focus shadow when invalid.
- `defaultValue` prop added (string | string[]) for uncontrolled init.
  Normalized to string[] inside the soma wrapper via untrack so the
  reference is intentionally non-reactive.
- `ItemDescription` part: new morfo part (kebab item-description, archetype
  description), new soma wrapper + new eidos wrapper. CSS gives muted
  color and 0.85em font-size; when the parent item is checked, the
  description inherits accent color.
- Value truncation: ensure `min-inline-size: 0` + `max-inline-size: 100%`
  on the trigger value so long labels ellipsis instead of overflowing.
- Highlighted vs checked distinction: the highlighted-only state now uses
  a lighter hover background, and an item that is both highlighted and
  checked gets an additional inset focus ring on top of the accent fill.

Demo at /uix/components/select adds an `invalid` switch, and three of the
six items now ship with a description (Apple / Pear / Carrot).

Verified in browser:
- triggerInvalid + aria-invalid = true after toggling switch.
- Description on non-checked item: rgb(123,123,123) (content-muted).
- Description on checked item: accent purple (inherits).
- svelte-check --threshold error → 0 errors / 0 warnings / 4574 files.

Deferred: SL3 readonly (rare use case), SL4 virtual scrolling (own task).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/uix/eidos/components/select/index.ts

@@ -5,6 +5,7 @@ import Indicator from './select-indicator.svelte'
 import Content from './select-content.svelte'
 import Viewport from './select-viewport.svelte'
 import Item from './select-item.svelte'
+import ItemDescription from './select-item-description.svelte'
 import ItemIndicator from './select-item-indicator.svelte'
 import Group from './select-group.svelte'
 import GroupHeading from './select-group-heading.svelte'
@@ -20,6 +21,7 @@ type SelectNamespace = typeof SelectComponent & {
 	Content: typeof Content
 	Viewport: typeof Viewport
 	Item: typeof Item
+	ItemDescription: typeof ItemDescription
 	ItemIndicator: typeof ItemIndicator
 	Group: typeof Group
 	GroupHeading: typeof GroupHeading
@@ -35,6 +37,7 @@ Select.Portal = Portal
 Select.Content = Content
 Select.Viewport = Viewport
 Select.Item = Item
+Select.ItemDescription = ItemDescription
 Select.ItemIndicator = ItemIndicator
 Select.Group = Group
 Select.GroupHeading = GroupHeading
@@ -53,6 +56,7 @@ export type {
 	SelectContentProps as ContentProps,
 	SelectViewportProps as ViewportProps,
 	SelectItemProps as ItemProps,
+	SelectItemDescriptionProps as ItemDescriptionProps,
 	SelectItemIndicatorProps as ItemIndicatorProps,
 	SelectGroupProps as GroupProps,
 	SelectGroupHeadingProps as GroupHeadingProps,

src/uix/eidos/components/select/select-item-description.svelte

@@ -0,0 +1,10 @@
+<script lang="ts">
+	import * as Select from '$soma/components/select';
+	import type { SelectItemDescriptionProps } from './types';
+
+	let { children, ...rest }: SelectItemDescriptionProps = $props();
+</script>
+
+<Select.ItemDescription {...rest}>
+	{@render children?.()}
+</Select.ItemDescription>

src/uix/eidos/components/select/select.css

@@ -166,9 +166,24 @@
 	cursor: not-allowed;
 }
 
+/* Invalid state — mirror field.css conventions. Border uses the risk palette
+   token; on focus we still keep the risk border (not the accent) so users
+   keep seeing the warning while interacting. */
+[data-select-trigger][data-invalid] {
+	border-color: var(--color-risk-border);
+}
+
+[data-select-trigger][data-invalid]:focus-visible,
+[data-select-trigger][data-invalid][data-state='open'] {
+	border-color: var(--color-risk-border);
+	box-shadow: 0 0 0 var(--select-trigger-border-width) var(--color-risk-border);
+}
+
 [data-select-value] {
+	display: block;
 	flex: 1 1 auto;
 	min-inline-size: 0;
+	max-inline-size: 100%;
 	overflow: hidden;
 	text-align: start;
 	text-overflow: ellipsis;
@@ -324,7 +339,10 @@
 		color var(--select-transition-duration) var(--select-transition-ease);
 }
 
-[data-select-item][data-highlighted] {
+/* Keyboard-focus background only when the item is NOT also checked. The
+   checked-and-highlighted case is handled below with an inset ring so the
+   accent track stays visible. */
+[data-select-item][data-highlighted]:not([data-state='checked']) {
 	background: var(--select-item-bg-highlighted);
 	color: var(--select-item-color-highlighted);
 }
@@ -334,11 +352,32 @@
 	color: var(--_select-accent-text);
 }
 
+/* Highlighted + checked: keep accent track but layer an inset focus shadow
+   so the row reads as "this checked item is the keyboard focus". */
+[data-select-item][data-highlighted][data-state='checked'] {
+	box-shadow: inset 0 0 0 var(--select-item-focus-ring-width, 2px) var(--_select-accent-border);
+}
+
 [data-select-item][data-disabled] {
 	color: var(--select-disabled-color);
 	cursor: not-allowed;
 }
 
+/* Secondary descriptive text under the item label (React Aria parity). */
+[data-select-item-description] {
+	display: block;
+	margin-block-start: var(--select-item-description-mt, 0.125rem);
+	color: var(--select-item-description-color, var(--color-content-muted));
+	font-size: var(--select-item-description-font-size, 0.85em);
+	line-height: var(--select-line-height);
+	opacity: 0.8;
+}
+
+[data-select-item][data-state='checked'] [data-select-item-description] {
+	color: inherit;
+	opacity: 0.85;
+}
+
 [data-select-item-indicator] {
 	display: inline-flex;
 	flex: 0 0 auto;

src/uix/eidos/components/select/types.ts

@@ -3,6 +3,7 @@ import type {
 	ContentProps,
 	GroupHeadingProps,
 	GroupProps,
+	ItemDescriptionProps,
 	ItemProps,
 	ProviderProps,
 	SeparatorProps,
@@ -48,6 +49,7 @@ export type SelectContentProps = ContentProps & {
 
 export type SelectViewportProps = ViewportProps
 export type SelectItemProps = ItemProps
+export type SelectItemDescriptionProps = ItemDescriptionProps
 export type SelectGroupProps = GroupProps
 export type SelectGroupHeadingProps = GroupHeadingProps
 export type SelectSeparatorProps = SeparatorProps

src/uix/morfo/components/select.ts

@@ -8,7 +8,7 @@ export const selectMorfo = {
 	texts: {
 		label: '#?components.select.label|Select'
 	},
-	apg: 'https://www.w3.org/WAI/ARIA/apg/patterns/combobox/',
+	apg: 'https://www.w3.org/WAI/ARIA/apg/patterns/listbox/',
 
 	events: [
 		{
@@ -52,9 +52,12 @@ export const selectMorfo = {
 			data: [
 				{ attr: 'data-state', values: ['open', 'closed'], value: v.stateRef('open') },
 				{ attr: 'data-disabled', value: v.propRef('disabled'), severity: 'optional' },
+				{ attr: 'data-invalid', value: v.propRef('invalid'), severity: 'optional' },
 				{ attr: 'data-type', values: ['single', 'multiple'], value: v.propRef('type') }
 			],
-			aria: []
+			aria: [
+				{ attr: 'aria-invalid', value: v.propRef('invalid'), severity: 'optional' }
+			]
 		},
 		{
 			name: 'Trigger',
@@ -68,6 +71,7 @@ export const selectMorfo = {
 			data: [
 				{ attr: 'data-state', values: ['open', 'closed'] },
 				{ attr: 'data-disabled', severity: 'optional' },
+				{ attr: 'data-invalid', severity: 'optional' },
 				{ attr: 'data-placeholder', severity: 'optional' }
 			],
 			aria: [
@@ -169,6 +173,16 @@ export const selectMorfo = {
 				}
 			]
 		},
+		{
+			name: 'ItemDescription',
+			kebab: 'item-description',
+			archetype: 'description',
+			kind: 'public',
+			defaultElement: 'span',
+			optional: true,
+			data: [],
+			aria: []
+		},
 		{
 			name: 'Group',
 			kebab: 'group',

src/uix/soma/components/select/components/select-item-description.svelte

@@ -0,0 +1,35 @@
+<script lang="ts">
+	import { readableActive, writableActive } from '$libs/reactive';
+	import { mergeProps } from '../../../props';
+	import { createId } from '../../../id';
+	import { SelectItemDescriptionProvider } from '../select-provider.svelte';
+	import type { SelectItemDescriptionProps } from '../types';
+
+	const uid = $props.id();
+
+	let {
+		ref = $bindable(null),
+		id = createId(uid, 'select-item-description'),
+		children,
+		child,
+		...restProps
+	}: SelectItemDescriptionProps = $props();
+
+	const state = SelectItemDescriptionProvider.create({
+		id: readableActive(() => id),
+		ref: writableActive(
+			() => ref,
+			(v) => (ref = v)
+		)
+	});
+
+	const mergedProps = $derived(mergeProps(restProps, state.props));
+</script>
+
+{#if child}
+	{@render child({ props: mergedProps })}
+{:else}
+	<span {...mergedProps}>
+		{@render children?.()}
+	</span>
+{/if}

src/uix/soma/components/select/components/select.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+	import { untrack } from 'svelte';
 	import { readableActive, writableActive } from '$libs/reactive';
 	import { mergeProps } from '../../../props';
 	import { createId } from '../../../id';
@@ -14,10 +15,21 @@
 		ref = $bindable(null),
 		id = createId(uid, 'select'),
 		type = 'single',
-		value = $bindable([]),
+		/**
+		 * Bindable selected value(s). When provided, takes precedence over
+		 * `defaultValue`. Use this for controlled usage.
+		 */
+		value = $bindable(),
+		/**
+		 * Initial value used only when `value` is undefined. Equivalent to
+		 * React-style "uncontrolled with initial value". Accepts a single
+		 * string or an array; coerced to `string[]` internally.
+		 */
+		defaultValue,
 		open = $bindable(false),
 		disabled = false,
 		required = false,
+		invalid = false,
 		name = '',
 		loop = false,
 		allowDeselect = false,
@@ -31,6 +43,17 @@
 		...restProps
 	}: SelectProps = $props();
 
+	// Normalize defaultValue → string[] and seed `value` if uncontrolled.
+	// Read once at init via untrack — defaultValue is intentionally not
+	// reactive (any later mutation is the consumer's responsibility via
+	// `value`).
+	if (value === undefined) {
+		value = untrack(() => {
+			if (defaultValue === undefined) return [];
+			return Array.isArray(defaultValue) ? [...defaultValue] : [defaultValue];
+		});
+	}
+
 	const state = SelectProvider.create({
 		id: readableActive(() => id),
 		ref: writableActive(
@@ -45,7 +68,7 @@
 			}
 		),
 		value: writableActive(
-			() => value,
+			() => value ?? [],
 			(v) => {
 				value = v;
 				onValueChange(v);
@@ -54,6 +77,7 @@
 		type: readableActive(() => type),
 		disabled: readableActive(() => disabled),
 		required: readableActive(() => required),
+		invalid: readableActive(() => invalid),
 		name: readableActive(() => name),
 		loop: readableActive(() => loop),
 		allowDeselect: readableActive(() => allowDeselect),
@@ -67,6 +91,7 @@
 
 {#snippet hiddenSelect()}
 	{#if name}
+		{@const safeValue = value ?? []}
 		<select
 			{...{ name, required, disabled, multiple: type === 'multiple' }}
 			aria-hidden="true"
@@ -74,9 +99,9 @@
 			style="position:absolute;pointer-events:none;opacity:0;width:0;height:0"
 		>
 			{#if type === 'single'}
-				<option value={value[0] ?? ''} selected>{value[0] ?? ''}</option>
+				<option value={safeValue[0] ?? ''} selected>{safeValue[0] ?? ''}</option>
 			{:else}
-				{#each value as v}
+				{#each safeValue as v}
 					<option value={v} selected>{v}</option>
 				{/each}
 			{/if}

src/uix/soma/components/select/exports.ts

@@ -4,6 +4,7 @@ export { default as Value } from './components/select-value.svelte';
 export { default as Content } from './components/select-content.svelte';
 export { default as Viewport } from './components/select-viewport.svelte';
 export { default as Item } from './components/select-item.svelte';
+export { default as ItemDescription } from './components/select-item-description.svelte';
 export { default as Group } from './components/select-group.svelte';
 export { default as GroupHeading } from './components/select-group-heading.svelte';
 export { default as Separator } from './components/select-separator.svelte';
@@ -18,6 +19,7 @@ export type {
 	SelectContentProps as ContentProps,
 	SelectViewportProps as ViewportProps,
 	SelectItemProps as ItemProps,
+	SelectItemDescriptionProps as ItemDescriptionProps,
 	SelectGroupProps as GroupProps,
 	SelectGroupHeadingProps as GroupHeadingProps,
 	SelectSeparatorProps as SeparatorProps,

src/uix/soma/components/select/select-provider.svelte.test.ts

@@ -51,6 +51,7 @@ function createSelectOpts() {
 		type: state<SelectType>('single'),
 		disabled: state(false),
 		required: state(false),
+		invalid: state(false),
 		name: state('choice'),
 		loop: state(false),
 		allowDeselect: state(false),

src/uix/soma/components/select/select-provider.svelte.ts

@@ -50,6 +50,7 @@ interface SelectOpts
 			type: SelectType;
 			disabled: boolean;
 			required: boolean;
+			invalid: boolean;
 			name: string;
 			loop: boolean;
 			allowDeselect: boolean;
@@ -116,6 +117,7 @@ export class SelectProvider {
 			props: {
 				disabled: () => this.opts.disabled.current,
 				required: () => this.opts.required.current,
+				invalid: () => this.opts.invalid.current,
 				type: () => this.opts.type.current,
 				multiple: () => this.opts.type.current === 'multiple'
 			},
@@ -384,8 +386,10 @@ export class SelectTriggerProvider {
 			'aria-controls': this.provider.contentId.current || undefined,
 			'aria-activedescendant': this.provider.highlightedId || undefined,
 			'aria-required': this.provider.opts.required.current || undefined,
+			'aria-invalid': this.provider.opts.invalid.current || undefined,
 			'data-state': getDataOpenClosed(this.provider.opts.open.current),
 			'data-disabled': boolToEmptyStrOrUndef(this.provider.opts.disabled.current),
+			'data-invalid': boolToEmptyStrOrUndef(this.provider.opts.invalid.current),
 			'data-placeholder': this.provider.opts.value.current.length === 0 ? '' : undefined,
 			disabled: this.provider.opts.disabled.current || undefined,
 			onclick: this.onclick,
@@ -718,6 +722,32 @@ export class SelectItemProvider {
 	);
 }
 
+// ── ItemDescription ──────────────────────────────────────────────────────────
+
+interface SelectItemDescriptionOpts extends WithRefOpts {}
+
+export class SelectItemDescriptionProvider {
+	readonly opts: SelectItemDescriptionOpts;
+	readonly runtimePart: SomaRuntimePart;
+	static create(opts: SelectItemDescriptionOpts) {
+		return new SelectItemDescriptionProvider(opts);
+	}
+
+	private constructor(opts: SelectItemDescriptionOpts) {
+		this.opts = opts;
+		const provider = SelectProvider.require();
+		this.runtimePart = provider.runtime.part('item-description', {
+			id: opts.id,
+			ref: opts.ref,
+			owner: this
+		});
+	}
+
+	readonly props = $derived.by(() =>
+		this.runtimePart.assert({ ...this.runtimePart.props } as const)
+	);
+}
+
 // ── Group ────────────────────────────────────────────────────────────────────
 
 interface SelectGroupOpts extends WithRefOpts {}

src/uix/soma/components/select/types.ts

@@ -22,8 +22,10 @@ export type SelectProps = WithChild<{
 	id?: string;
 	/** Selection mode. @default 'single' */
 	type?: SelectType;
-	/** Selected value(s). Bindable. @default [] */
+	/** Selected value(s). Bindable. When provided, takes precedence over `defaultValue`. @default [] */
 	value?: string[];
+	/** Initial value used only when `value` is undefined. @default undefined */
+	defaultValue?: string | string[];
 	/** Callback on value change. */
 	onValueChange?: OnChangeFn<string[]>;
 	/** Whether the listbox is open. Bindable. @default false */
@@ -36,6 +38,8 @@ export type SelectProps = WithChild<{
 	disabled?: boolean;
 	/** @default false */
 	required?: boolean;
+	/** Marks the trigger as having an invalid value. Emits `data-invalid` and `aria-invalid`. @default false */
+	invalid?: boolean;
 	/** Form field name. Renders hidden <select> when set. */
 	name?: string;
 	/** Wrap keyboard navigation at boundaries. @default false */
@@ -131,6 +135,12 @@ export type SelectItemProps = WithChild<
 > &
 	Without<PrimitiveDivAttributes, {}>;
 
+export type SelectItemDescriptionProps = WithChild<{
+	/** Unique identifier. Auto-generated if omitted. */
+	id?: string;
+}> &
+	Without<PrimitiveSpanAttributes, {}>;
+
 export type SelectGroupProps = WithChild<{
 	/** Unique identifier. Auto-generated if omitted. */
 	id?: string;

web/routes/uix/components/select/+page.svelte

@@ -13,17 +13,23 @@
 
 	type Tab = 'live' | 'api' | 'morfo' | 'sema' | 'recipe' | 'a11y';
 	type SelectMode = 'single' | 'multiple';
-	type Option = { value: string; label: string; group: string; disabled?: boolean };
+	type Option = {
+		value: string;
+		label: string;
+		group: string;
+		disabled?: boolean;
+		description?: string;
+	};
 	type TraceEntry = { event: string; family: string; intent?: string; at: number };
 
 	const uix = getActiveUix();
 	const params = page.url.searchParams;
 
 	const options: readonly Option[] = [
-		{ value: 'apple', label: 'Apple', group: 'Fruit' },
+		{ value: 'apple', label: 'Apple', group: 'Fruit', description: 'Crisp, sweet, ubiquitous' },
-		{ value: 'pear', label: 'Pear', group: 'Fruit' },
+		{ value: 'pear', label: 'Pear', group: 'Fruit', description: 'Soft, mellow autumn fruit' },
 		{ value: 'orange', label: 'Orange', group: 'Fruit' },
-		{ value: 'carrot', label: 'Carrot', group: 'Vegetables' },
+		{ value: 'carrot', label: 'Carrot', group: 'Vegetables', description: 'Root, high in beta-carotene' },
 		{ value: 'mushroom', label: 'Mushroom', group: 'Vegetables', disabled: true },
 		{ value: 'pepper', label: 'Pepper', group: 'Vegetables' }
 	];
@@ -47,6 +53,7 @@
 	let mode = $state<SelectMode>('single');
 	let disabled = $state(params.get('perm.disabled') === 'true');
 	let required = $state(false);
+	let invalid = $state(false);
 	let allowDeselect = $state(true);
 	let size = $state<SelectSize>('md');
 	let variant = $state<SelectVariant>('surface');
@@ -198,6 +205,7 @@
 				type={mode}
 				{disabled}
 				{required}
+				{invalid}
 				{allowDeselect}
 				{size}
 				{variant}
@@ -225,7 +233,12 @@
 											data-perm-step={!disabled && option.value === 'pear' ? '1' : undefined}
 											data-perm-label={!disabled && option.value === 'pear' ? 'select pear' : undefined}
 										>
-											<span>{option.label}</span>
+											<span style="display: flex; flex-direction: column; min-inline-size: 0;">
+												<span>{option.label}</span>
+												{#if option.description}
+													<Select.ItemDescription>{option.description}</Select.ItemDescription>
+												{/if}
+											</span>
 											<Select.ItemIndicator />
 										</Select.Item>
 									{/each}
@@ -311,6 +324,10 @@
 					<input type="checkbox" bind:checked={required} />
 					<span data-uix-switch-label>required</span>
 				</label>
+				<label data-uix-switch>
+					<input type="checkbox" bind:checked={invalid} />
+					<span data-uix-switch-label>invalid</span>
+				</label>
 				<label data-uix-switch>
 					<input type="checkbox" bind:checked={allowDeselect} />
 					<span data-uix-switch-label>allowDeselect</span>