Numeric spacing scale

Context

KDS spacing already had a density-aware t-shirt scale (--kds-space-{xs,sm,md,lg,xl} = calc(<px> × var(--kds-density-scale)), in the density :root of assets/css/base.css), and the semantic tokens (--pad-x, --gap-field, …) are integer multiples of a 2px base unit (internal/tokens/noncolour.go). What was missing — and what gov.br's Padrão Digital publishes explicitly — is a numeric scale (spacing-scale-*). This spec adds the numeric scale as the single source, re-expresses the t-shirt names as aliases of it, and documents the semantic + gov.br mappings.

R1 — The scale

--kds-space-<n> = n × --kds-space-unit, where --kds-space-unit is 2px. The index is the multiple, so the scale faithfully names the geometry KDS spacing already used — no value is invented. Contiguous n ∈ 0..12 (0–24px at default density) is published in the density :root (assets/css/base.css, served in the KDS dist tokens at https://kds.koder.dev). Larger steps extend the SAME rule (--kds-space-16 = calc(16 × unit × scale)); the rule, not an enumerated ceiling, is normative.

R2 — Density relation

Each step n ≥ 1 reads the density multiplier: --kds-space-<n>: calc(<n> * var(--kds-space-unit) * var(--kds-density-scale, 1)). --kds-density-scale is 1 default, 0.8 compact, 1.2 comfortable (specs/themes/density.kmd R2). A surface rescales all scale-sourced spacing by setting data-density alone. --kds-space-0 is a literal 0 (density-invariant).

R3 — T-shirt aliases (single source)

The pre-existing t-shirt tokens are aliases of numeric steps — same computed value, one source of truth (no parallel definitions to drift):

R4 — Semantic-token mapping

The semantic spacing tokens (internal/tokens/noncolour.go) are exact scale steps:

Migrating the semantic tokens to literal var(--kds-space-<n>) (so they too become density-aware) is a follow-up — it changes their behavior under non-default density, so it is deliberately separate. Until then the semantic tokens keep their raw px (density-invariant).

R5 — gov.br cross-map

gov.br's spacing-scale maps onto even indices (its base is 8px = 4 units):

Higher gov.br steps (4x…10x) resolve through R1's extension rule (--kds-space-16…--kds-space-40), giving the govbr DS a spacing foundation in the KDS scale with no parallel vocabulary.

Não-escopo

• Component minimum dimensions and per-mode padding deltas — specs/themes/density.kmd R2/R3, not here.
• The semantic-token alias migration (R4) — its own slice.
• Rust/non-CSS token mirrors — the scale's canonical dist surface is the KDS CSS custom properties; a Rust mirror follows design-RFC-006 if a native consumer needs it.