fix(client): lint conformance for the preference services

Replace optional chains on always-present globals with the repo's
typeof guards (store.ts precedent), drop the non-null assertion by
failing loud on an impossible registry miss, and fix two arrow-parens
slips; cover the no-localStorage boot path in both service suites.

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

@@ -87,7 +87,8 @@ export class ThemeService {
   constructor(ctx: Context) {
     this.ctx = ctx
     this.preference = restorePreference()
-    this.media = globalThis.matchMedia?.('(prefers-color-scheme: dark)')
+    // Non-browser runs (node e2e booting the client tree) have no matchMedia.
+    this.media = typeof matchMedia === 'undefined' ? undefined : matchMedia('(prefers-color-scheme: dark)')
     this.snapshot = this.buildSnapshot()
     if (this.media !== undefined) {
       const media = this.media
@@ -157,8 +158,9 @@ export class ThemeService {
       : this.preference
     // Both built-ins always exist; a registered preference id resolves or has
     // been reset by its disposer, so the lookup cannot miss.
-    /* v8 ignore next -- the ?? arm needs a registry without light/dark, which register()/dispose() cannot produce */
-    const active = this.themes.find(t => t.id === resolvedId) ?? this.themes[0]!
+    const active = this.themes.find(t => t.id === resolvedId)
+    /* v8 ignore next 2 -- needs a registry without light/dark, which register()/dispose() cannot produce */
+    if (active === undefined) throw new Error(`theme registry lost "${resolvedId}"`)
     return Object.freeze({
       preference: this.preference,
       active,
@@ -176,8 +178,10 @@ export class ThemeService {
 
 /** Read the persisted preference; unknown or unreadable values fall back to the default. */
 function restorePreference(): ThemePreference {
+  // Non-browser runs (node e2e booting the client tree) have no localStorage.
+  if (typeof localStorage === 'undefined') return DEFAULT_PREFERENCE
   try {
-    const stored = globalThis.localStorage?.getItem(STORAGE_KEY)
+    const stored = localStorage.getItem(STORAGE_KEY)
     if (stored === 'light' || stored === 'dark' || stored === 'system') return stored
   } catch {
     // Storage access can throw (privacy mode); the default below covers it.
@@ -187,8 +191,9 @@ function restorePreference(): ThemePreference {
 
 /** Persist the preference; storage failures are non-fatal (preference resets next boot). */
 function persistPreference(preference: ThemePreference): void {
+  if (typeof localStorage === 'undefined') return
   try {
-    globalThis.localStorage?.setItem(STORAGE_KEY, preference)
+    localStorage.setItem(STORAGE_KEY, preference)
   } catch {
     // Storage access can throw (privacy mode / quota); the preference simply
     // does not survive the session.

packages/client/ui-theme/tests/theme.spec.ts

@@ -88,6 +88,18 @@ describe('ThemeService', () => {
     expect(events.map(e => e.revision)).toEqual([1, 2, 3, 4])
   })
 
+  it('runs without localStorage (node boots): defaults on read, no-op on write', () => {
+    vi.stubGlobal('localStorage', undefined)
+    try {
+      const { theme } = make()
+      expect(theme.getTheme().preference).toBe('system')
+      theme.setTheme('dark')
+      expect(theme.getTheme().preference).toBe('dark')
+    } finally {
+      vi.unstubAllGlobals()
+    }
+  })
+
   describe('prefers-color-scheme resolution (stubbed matchMedia)', () => {
     type Listener = () => void
     const stubMedia = (initialMatches: boolean) => {