five dialects became one language — Defaults is the organization layer

/* the five dialects (before) — one ambient channel per axis,
   each with its own key, its own helper, its own ?? chain: */
density     DENSITY_KEY + plugin seam    resolveDensity(e, ctx)
medium      read-only projection         getMedium()
hue         runtime adapter              createHueContext()
button paint  BUTTON_GROUP_KEY zone      variant ?? scope.variant
entity depth  entity.svelte.ts accum     provideEntity()

/* the reads lived inline, in every component: */
variant ?? group?.variant ?? 'outline'        // press-button, before

plugins (print & other cross-cutting)   ← kernel never knows components,
   ↓                                       intervenes on AXIS VALUES only
axes (few, structural)
   density │ paint                          ← the two collected into slots
   entity-depth │ medium (read-only) │ hue  ← keep their own mechanisms
   ↓ ONE read point per family
<Component>Defaults                          ← this change: the organization layer
   ↓ projects
resolved props (full values, inferred types, getter-endorsed)
   ↓ overridden by
explicit props (omit → the factory decides)

// kbd-defaults.svelte.ts — the family's ONE ambient contract
import { defineComponentDefaults, defineLiteralSlot } from '@lib/defaults.svelte';
import { densitySlot } from '@lib/density.svelte';

// the named slot constant — the values tuple IS the union's source:
// default ∈ values is compile-locked, an own outside the tuple
// never compiles
export const kbdVariantSlot = defineLiteralSlot(['fill', 'tonal', 'outline'], 'tonal');

// the union, looked up — no hand-declared twin beside the values
export type KbdVariant = ReturnType<typeof kbdVariantSlot>;

export const KbdDefaults = defineComponentDefaults({
  variant: kbdVariantSlot,  // explicit ?? own, reads no context (class b)
  density: densitySlot(),   // no family own — a no-opinion slot
});

<!-- inside press-button.svelte: the family's SINGLE audited read point.
     d.variant / d.density are fully typed and already resolved. -->
const d = $derived(PressButtonDefaults.resolve({ variant, density }));

// slot resolution law, one line, every slot the same:
//    explicit prop ?? ambient axis ?? own default
// a no-opinion slot (density with no own) has no last resort: it
// resolves to no opinion, stamps nothing, and the ambient css scope
// channel keeps flowing (the fleet law).

// the literal family's scalar faces — trimmed from two families:
export const descriptionsBorderedSlot = defineLiteralSlot([false, true], false);

export const sheetSizeSlot = defineOpenSlot<string>('24rem');
// ↑ the drawer extent is a free CSS length — no closed union to
//   enumerate; a future size axis would first have to close the
//   union, at which point this slot migrates back to the values form.

// and the upgrade path stays documented in the file header: freeze a
// table row → promote to definePaintSlot(values, own) — kbd's
// convention.

// tabs.svelte — inherit-then-provide, the complete frozen form:
// 1. eager-capture the PARENT's value (argument position = statement
//    time, BEFORE this component writes its own key)
const resolvedDensity = $derived.by(
  ((inherited) => () => resolveDensity(density, inherited))(getDensityContext()),
);
provideDensity(() => resolvedDensity);

// 2. the family Defaults read stacks on the lane: the slot's ambient
//    read lands on the provider ABOVE, terminates at the captured
//    parent — one resolution per subtree, value pinned by tests
const d = $derived(TabsDefaults.resolve({ density }));