refactor(client): shared declaration-aware registration deferral

The five settings-surface registrants carried near-identical
spec-check/ledger-judge/subscribe scaffolding (three jscpd clones);
ui-slots now owns deferRegistration() — ledger-judged presence, refresh
for registrant-localized labels, one-call disposal — and every
registrant shrinks to its registration body.

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

@@ -5,6 +5,7 @@
  * discipline: packages/client/AGENTS.md.
  */
 import type { ClientContext } from '@deepseek-ai/dsh-client-runtime/client'
+import { deferRegistration } from '@deepseek-ai/dsh-client-ui-slots'
 // 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).
@@ -31,37 +32,20 @@ export function apply(ctx: ClientContext): void {
     ]
     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({
+    const deferred = deferRegistration(ctx.slots, 'settings.section', ModelsSection, () =>
+      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()
+      }, ModelsSection))
+    // Nav labels are registrant-localized: refresh on locale change so the
+    // ledger carries fresh text (the version bump re-renders the shell).
+    const offLocale = ctx.on('locale/change', () => { deferred.refresh() })
     return () => {
       offLocale()
-      unsubscribe()
-      dispose?.()
+      deferred.dispose()
     }
   }, 'ui-models: settings section registration')
 }