feat(daemon): enumerate installed extension skills locally

docs/design/daemon-extension-skill-catalog.md

@@ -0,0 +1,71 @@
+# Daemon extension Skill catalog
+
+This implements stage 2 of #11274. The daemon-local workspace Skill provider
+currently supplies an empty active-extension list, so its first response omits
+installed extension Skills when no child snapshot exists.
+
+Use an unbound `ExtensionManager` for the selected workspace to load installed
+extensions through the existing consistent store reader. Supply active
+extensions to `SkillManager`, preserving project > user > extension > bundled
+precedence. Append inactive extension Skills as management entries with the
+existing `inactive_extension` status, retaining their identity and metadata.
+Resolve settings and extension Skill defaults/overrides with the existing
+parsers. A settings opt-in does not enable an inactive parent extension.
+Resolve localized extension names with the existing language setting and locale
+helpers, without changing the daemon process language. The resolved locale is
+part of the provider cache key — recomputed from freshly loaded settings on
+every call — because a language change reaches no invalidation point.
+
+Keep the lightweight Config surface: do not construct a runtime Config, start a
+child, initialize MCP, execute hooks, or install watchers. Honor safe mode,
+disabled discovery levels and workspace trust; inert untrusted inventory must
+not load workspace settings or extension runtime context.
+`skills.disabledLevels` gates extension _discovery_ only; inactive-extension
+management entries are appended regardless, matching the child producer.
+
+Failure handling is two-tier. An unreadable extensions _root_ (or a configured
+skills base directory) keeps the documented all-or-nothing behavior: an
+uninitialized error status. The explicit `readdir` probe is what surfaces that
+state — the store loader swallows listing errors, so without the probe an
+unlistable root would silently yield an initialized catalog missing every
+extension Skill. A fault _inside_ the extension load itself (corrupt store
+state, a dangling extension symlink, lock contention) degrades only the
+extension entries instead: the catalog is served initialized with the project,
+user and bundled Skills, the failure is logged to the daemon's stderr, and the
+degraded build is not cached so the next read retries extension enumeration.
+
+Cache installs are guarded by a per-workspace invalidation epoch, so an
+invalidation delivered while a cold build is in flight cannot be undone by
+that build, and concurrent cold builds of one workspace are coalesced. Startup
+`--enable-extension` overrides are not propagated here (the daemon's child
+spawn generally does not carry them either).
+
+The implementation and collocated regressions live in the daemon-local provider.
+Tests cover real manifests, active/inactive state, source collisions, persisted
+Skill settings, safe/untrusted contexts, explicit and mid-build cache
+invalidation, language changes, the extension-load failure domain, unreadable
+directory roots and discovery-level gating. E2E evidence uses an isolated home
+and a daemon with no child session.
+
+The facade still prefers child snapshots in this stage. Replacing that source,
+changing toggle/refresh semantics, adding configured-state fields and changing
+Web Shell projections belong to later PRs. No public schema changes are needed.
+
+Known later-stage items (recorded during review, deliberately not in this
+stage):
+
+- The sibling `/workspace/extensions` route resolves its locale through a
+  settings load that admits the workspace `.env` into the daemon's
+  process-global environment, so a workspace `QWEN_CODE_LANG` can diverge the
+  two panels of one page. This provider follows the documented daemon
+  convention (`skipLoadEnvironment`); fixing the leak belongs to that route.
+- The inactive-append and sort assembly is a second copy of the child's
+  (`acpAgent.ts`); extracting it into the shared
+  `runtime/workspace-skills-mapping.ts` module — keeping the child's
+  `level:extensionName:name` dedupe key — belongs to a follow-up.
+- Retaining the cached `ExtensionManager` across skill-settings invalidations
+  behind `refreshCacheIfSourcesChanged` needs invalidation provenance
+  (extension-store mutation vs skill-settings mutation) that the current
+  call sites do not carry.
+- The active-Skill `enabled` judgment mirrors `Config.isSkillEnabled`;
+  sharing that decision with core config belongs to a follow-up.

packages/cli/src/i18n/index.ts

@@ -223,7 +223,9 @@ function interpolate(
 }
 
 // Language setting helpers
-function resolveLanguage(lang: SupportedLanguage | 'auto'): SupportedLanguage {
+export function resolveLanguage(
+  lang: SupportedLanguage | 'auto',
+): SupportedLanguage {
   if (lang === 'auto') {
     return detectSystemLanguage();
   }