refactor(gui): features register their own settings surfaces

Settings collaboration direction (recorded in the note): the shell only
provides composition faces — feature plugins register themselves. The
General section moves into the ui-settings shell (order 0, skeleton
rows) and declares the settings.general.item list slot; locale registers
the Language row and ui-theme the Appearance row (each with its own
store mirror, dictionaries, and ledger-judged deferral); the
ui-settings-general package is gone. ui-settings-models becomes
ui-models — a feature package that contributes its Settings section
rather than a settings-owned satellite. The item-slot SlotMap entry is
authored in the ui-settings contract and repeated verbatim in
locale/ui-theme (reference-cycle avoidance; declaration merging keeps
the copies identical).

packages/client/ui-models/src/client/ModelsSection.tsx

@@ -0,0 +1,13 @@
+/**
+ * Models settings section: an intentionally empty content column — the nav
+ * entry exists so the section slot composition is visible; model management
+ * lands in a later phase.
+ */
+
+/**
+ * Render the (empty) Models section content column.
+ * @returns null — no content this phase.
+ */
+export function ModelsSection() {
+  return null
+}

packages/client/ui-models/src/client/index.ts

@@ -0,0 +1,67 @@
+/**
+ * Models settings section plugin, browser half. Registers the `models` nav
+ * entry into the shell-declared `settings.section` list slot; the content
+ * column is intentionally empty until model management lands. Export
+ * discipline: packages/client/AGENTS.md.
+ */
+import type { ClientContext } from '@deepseek-ai/dsh-client-runtime/client'
+// Type-only: pulls the shell's SlotMap merge (the 'settings.section' entry).
+import type {} from '@deepseek-ai/dsh-client-ui-settings/client'
+// Type-only: pulls the locale plugin's Context merge (ctx.locale).
+import type {} from '@deepseek-ai/dsh-client-locale/client'
+import { ModelsSection } from './ModelsSection.tsx'
+
+/**
+ * Required services (cordis fiber inject). The target slot is declared by
+ * ui-settings' apply, whose activation order relative to this one is NOT
+ * constrained; registration goes through declaration-aware deferral.
+ */
+export const inject = ['slots', 'locale']
+
+/**
+ * Register the Models section once the `settings.section` declaration is on
+ * the ledger.
+ * @param ctx - client root context.
+ */
+export function apply(ctx: ClientContext): void {
+  ctx.effect(() => {
+    const disposers = [
+      ctx.locale.register('settings.models', 'zh', { nav: '模型' }),
+      ctx.locale.register('settings.models', 'en', { nav: 'Models' }),
+    ]
+    return () => { for (const dispose of disposers) dispose() }
+  }, 'ui-models: nav copy dictionaries')
+  // Declaration-aware registration; the LEDGER is the has-registered judge
+  // (not a local flag): after an HMR collapse re-declares the slot, the
+  // cascade already removed our entry, and a stale disposer must not block
+  // the re-registration.
+  ctx.effect(() => {
+    let dispose: (() => void) | undefined
+    const tryRegister = (): void => {
+      if (ctx.slots.spec('settings.section') === undefined) return
+      if (ctx.slots.entries('settings.section').some(e => e.component === ModelsSection)) return
+      dispose = ctx.slots.register({
+        name: 'settings.section',
+        id: 'models',
+        order: 10,
+        label: ctx.locale.bind('settings.models')('nav'),
+      }, ModelsSection)
+    }
+    // Nav labels are registrant-localized: re-register on locale change so
+    // the ledger carries fresh text (the version bump re-renders the shell).
+    // Dispose-then-requery: after an HMR collapse the disposer is stale and
+    // the ledger/spec re-check keeps this path an idempotent no-op.
+    const offLocale = ctx.on('locale/change', () => {
+      dispose?.()
+      dispose = undefined
+      tryRegister()
+    })
+    const unsubscribe = ctx.slots.subscribe('settings.section', () => { tryRegister() })
+    tryRegister()
+    return () => {
+      offLocale()
+      unsubscribe()
+      dispose?.()
+    }
+  }, 'ui-models: settings section registration')
+}

packages/client/ui-models/src/css-modules.d.ts

@@ -0,0 +1,6 @@
+declare module '*.module.css' {
+  const classes: Record<string, string>
+  export default classes
+}
+
+declare module '*.css'

packages/client/ui-models/src/index.ts

@@ -0,0 +1,4 @@
+/** Host loader entry for the browser implementation exported from `./client`. */
+
+/** Host plugin body — no host-side behavior for the models settings plugin. */
+export function apply(): void {}

packages/client/ui-models/src/invariant.ts

@@ -0,0 +1,31 @@
+/**
+ * Package-owned invariant companion for `@deepseek-ai/dsh-client-ui-models`.
+ * @module @deepseek-ai/dsh-client-ui-models/invariant
+ */
+
+/* jscpd:ignore-start */
+import type { Context } from 'cordis'
+import type { InvariantInstaller } from '@deepseek-ai/dsh-invariants'
+
+const PACKAGE_NAME = '@deepseek-ai/dsh-client-ui-models'
+
+/** Cordis companion plugin name. */
+export const name = 'client-ui-models-invariant'
+/** Service required before the companion can reserve package ownership. */
+export const inject = ['invariants']
+
+/**
+ * No runtime invariant: a nav-entry-only section plugin rendering a fixed
+ * empty content column — it emits no cordis events and owns no cross-plugin
+ * mutable relation.
+ */
+const install: InvariantInstaller = () => {}
+
+/**
+ * Register this package's invariant companion.
+ * @param ctx - Cordis context carrying the invariant service.
+ * @returns the installed registration's disposer after setup succeeds.
+ */
+export const apply = (ctx: Context): Promise<() => void> =>
+  Promise.resolve(ctx.invariants.register(PACKAGE_NAME, install))
+/* jscpd:ignore-end */