docs(i18n): record D-102 (i18n routing) + ui-design skill rule

Document the T-462 i18n architecture: ext-id namespaces auto-loaded on
activation, a 'core' catalog for framework chrome, the null-safe
ClideSettings.i18n read facade, contribution titleKey/labelKey fields, and the
assets/i18n/<locale>/<namespace>.json locale-dir layout. Add the "route
user-facing strings through the catalog" rule to the ui-design skill.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.claude/skills/ui-design/SKILL.md

@@ -45,6 +45,13 @@ These apply across every reference and every surface:
   widget must set it explicitly. `clideMonoFamily` / `clideUiFamily` are the
   facade's defaults — don't read them directly in new widgets (D-101). Same
   facade exposes `ClideSettings.theme.of(context)` and `.i18n.of(context)`.
+- User-facing strings resolve through the catalog, never a hardcoded literal
+  (D-21/D-102): `ClideSettings.i18n.string(context, 'dotted.key', namespace:
+  <ext id or 'core'>, placeholder: '<English>')` (or `.interpolated` for
+  templated). Add the key→English to `assets/i18n/en_us/<namespace>.json`. The
+  `placeholder` is the English fallback; the extension's own id is its
+  namespace (framework chrome uses `core`). Contribution manifests carry
+  `titleKey`/`labelKey` for the same reason.
 
 ## Conversation-panel cards (T-305)
 

governance/README.md

@@ -143,6 +143,7 @@ You might also want, project-permitting:
 - [D-99: Remote session identity keyed on (host, workspace)](decisions/architecture.md#d-99-remote-session-identity-keyed-on-host-workspace) — _architecture_
 - [D-100: Fence `dart:ffi` behind conditional imports + web stubs to keep the web/WASM target compiling](decisions/tooling.md#d-100-fence-dartffi-behind-conditional-imports--web-stubs-to-keep-the-webwasm-target-compiling) — _tooling_
 - [D-101: ClideSettings — one live-preferences access facade](decisions/architecture.md#d-101-clidesettings--one-live-preferences-access-facade) — _architecture_
+- [D-102: i18n routing — ext-id namespaces, `core` catalog, ClideSettings.i18n facade, contribution keys](decisions/accessibility.md#d-102-i18n-routing--ext-id-namespaces-core-catalog-clidesettingsi18n-facade-contribution-keys) — _accessibility_
 
 ## Open questions
 

governance/decisions/accessibility.md

@@ -32,4 +32,15 @@ A11y + i18n are Tier-0 contracts, not Tier-6 polish.
 - **Cost:** Two extra theme files per "named" theme when we add a11y variants. The bundled-theme contrast gate ([D-22](#d-22-wcag-aa-contrast-gate-on-bundled-themes)) needs a baseline/extended split so the named themes don't fail the strict pairs.
 - **Raised by:** 2026-05-17 — user intervened mid-T-114 when I had retuned `clide`/`midnight`/`paper`/`terminal` palette entries to satisfy the expanded `canonicalPairs`; reverted, decision written, T-114 will follow this rule.
 
+### D-102: i18n routing — ext-id namespaces, `core` catalog, ClideSettings.i18n facade, contribution keys
+- **Date:** 2026-06-19
+- **Decision:** Implements [D-21](#d-21-i18n-is-a-tier-0-contract-fframe-pattern--locale-fallback-chain) across the whole app (epic T-462).
+  - **Namespaces:** an extension's catalog namespace IS its id (`builtin.<name>`); the ExtensionManager eager-loads it on activation, so a built-in localizes with no hand-maintained registry. Framework chrome outside any extension (`lib/widgets`, `lib/kernel`, the shared reader chrome) resolves under one **`core`** namespace, preloaded at boot.
+  - **Read path:** widgets resolve through the single [D-101](architecture.md) facade — `ClideSettings.i18n.string(context, key, namespace:, placeholder:)` (+ `.interpolated`) — null-safe (returns the placeholder when no kernel is in scope, so primitives render in isolated tests).
+  - **Manifest labels:** `CommandContribution` carries `titleKey`/`i18nNamespace`; the palette and menu resolve via a shared `localizedCommandTitle`, and the palette's fuzzy search matches the localized title. The settings schema carries `i18nNamespace`+`titleKey` on the category and `labelKey`/`helpKey`/option `labelKey` beneath it, threaded down by the renderer.
+  - **Storage:** catalogs are bundled assets at `assets/i18n/<locale>/<namespace>.json` — the locale is a *directory* (`en_us`, future `nl_nl`, `nl_be`, `en_eu`, …), so a new language is a new folder of the same namespace files, no renames.
+- **Rationale:** makes a complete translation set (e.g. a Dutch pack) a pure data drop — no code. ext-id namespaces need no registry; the facade keeps one widget-facing read path for theme/fonts/i18n (D-101); the locale-dir layout is cleaner to maintain and mirrors how an external extension ships its own catalog.
+- **Cost:** every extension's manifest gains optional key fields, and framework primitives now depend on the (null-safe) facade. The pure-data search matcher (`settingsFieldMatches`) still matches the English label — display localizes, search-by-translation does not (acceptable refinement).
+- **Raised by:** 2026-06-19, epic T-462 (i18n everywhere). Builds on [D-101](architecture.md).
+
 ---