diff --git a/frontend/taskdeck-web/src/store/featureFlagStore.ts b/frontend/taskdeck-web/src/store/featureFlagStore.ts
index 324c1d0b2..77ef8f60c 100644
--- a/frontend/taskdeck-web/src/store/featureFlagStore.ts
+++ b/frontend/taskdeck-web/src/store/featureFlagStore.ts
@@ -4,9 +4,23 @@ import type { FeatureFlags } from '../types/feature-flags'
 import { defaultFeatureFlags } from '../types/feature-flags'
 
 const FLAGS_KEY = 'taskdeck_feature_flags'
+const FEATURE_FLAG_KEYS = Object.keys(defaultFeatureFlags) as Array<keyof FeatureFlags>
+
+function normalizeFeatureFlags(raw: unknown): FeatureFlags {
+  const normalized: FeatureFlags = { ...defaultFeatureFlags }
+  if (!raw || typeof raw !== 'object' || Array.isArray(raw)) return normalized
+
+  const candidate = raw as Record<string, unknown>
+  for (const key of FEATURE_FLAG_KEYS) {
+    if (typeof candidate[key] === 'boolean') normalized[key] = candidate[key]
+  }
+  return normalized
+}
 
 export const useFeatureFlagStore = defineStore('featureFlags', () => {
   const flags = ref<FeatureFlags>({ ...defaultFeatureFlags })
+  const persistenceError = ref<string | null>(null)
+  let hasUnsavedChanges = false
 
   function isEnabled(flag: keyof FeatureFlags): boolean {
     return flags.value[flag]
@@ -23,27 +37,40 @@ export const useFeatureFlagStore = defineStore('featureFlags', () => {
   }
 
   function persist() {
-    localStorage.setItem(FLAGS_KEY, JSON.stringify(flags.value))
+    try {
+      localStorage.setItem(FLAGS_KEY, JSON.stringify(normalizeFeatureFlags(flags.value)))
+      hasUnsavedChanges = false
+      persistenceError.value = null
+    } catch {
+      hasUnsavedChanges = true
+      persistenceError.value = 'Feature flag changes are active for this session but could not be saved in browser storage.'
+    }
   }
 
   function restore() {
-    const saved = localStorage.getItem(FLAGS_KEY)
-    if (saved) {
-      try {
-        const parsed = JSON.parse(saved)
-        flags.value = { ...defaultFeatureFlags, ...parsed }
-      } catch {
-        flags.value = { ...defaultFeatureFlags }
+    if (hasUnsavedChanges) return
+
+    try {
+      const saved = localStorage.getItem(FLAGS_KEY)
+      if (!saved) {
+        persistenceError.value = null
+        return
       }
+      flags.value = normalizeFeatureFlags(JSON.parse(saved) as unknown)
+      persistenceError.value = null
+    } catch {
+      flags.value = { ...defaultFeatureFlags }
+      persistenceError.value = 'Feature flags could not be loaded from browser storage; defaults are active.'
     }
   }
 
   const allEnabled = computed(() =>
-    Object.values(flags.value).every(v => v)
+    FEATURE_FLAG_KEYS.every((key) => flags.value[key])
   )
 
   return {
     flags,
+    persistenceError,
     isEnabled,
     setFlag,
     resetAll,
diff --git a/frontend/taskdeck-web/src/tests/store/featureFlagStore.spec.ts b/frontend/taskdeck-web/src/tests/store/featureFlagStore.spec.ts
index 572ce5e6b..e1d95591e 100644
--- a/frontend/taskdeck-web/src/tests/store/featureFlagStore.spec.ts
+++ b/frontend/taskdeck-web/src/tests/store/featureFlagStore.spec.ts
@@ -1,4 +1,4 @@
-import { describe, it, expect, beforeEach } from 'vitest'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 import { setActivePinia, createPinia } from 'pinia'
 import { useFeatureFlagStore } from '../../store/featureFlagStore'
 import { defaultFeatureFlags } from '../../types/feature-flags'
@@ -12,6 +12,10 @@ describe('featureFlagStore', () => {
     store = useFeatureFlagStore()
   })
 
+  afterEach(() => {
+    vi.restoreAllMocks()
+  })
+
   describe('default flags', () => {
     it('should match configured defaults', () => {
       for (const key of Object.keys(defaultFeatureFlags) as (keyof typeof defaultFeatureFlags)[]) {
@@ -67,6 +71,146 @@ describe('featureFlagStore', () => {
       }
     })
 
+    it('clears a previous load error after a later restore succeeds', () => {
+      localStorage.setItem('taskdeck_feature_flags', 'not-valid-json')
+      store.restore()
+      expect(store.persistenceError).toContain('could not be loaded')
+
+      localStorage.setItem('taskdeck_feature_flags', JSON.stringify({ newAuth: false }))
+      store.restore()
+
+      expect(store.persistenceError).toBeNull()
+      expect(store.isEnabled('newAuth')).toBe(false)
+    })
+
+    it('restores only declared boolean flag values', () => {
+      localStorage.setItem('taskdeck_feature_flags', JSON.stringify({
+        newShell: 0,
+        newAuth: 'false',
+        newAccess: false,
+        devTools: 'true',
+        ollama: true,
+        unknownFlag: true,
+      }))
+
+      store.restore()
+
+      expect(store.isEnabled('newShell')).toBe(defaultFeatureFlags.newShell)
+      expect(store.isEnabled('newAuth')).toBe(defaultFeatureFlags.newAuth)
+      expect(store.isEnabled('devTools')).toBe(defaultFeatureFlags.devTools)
+      expect(store.isEnabled('newAccess')).toBe(false)
+      expect(store.isEnabled('ollama')).toBe(true)
+      expect(Object.keys(store.flags).sort()).toEqual(Object.keys(defaultFeatureFlags).sort())
+      expect((store.flags as Record<string, unknown>).unknownFlag).toBeUndefined()
+    })
+
+    it.each(['null', '[false]', '"text"', '42'])(
+      'uses defaults for a non-object persisted payload %s',
+      (payload) => {
+        localStorage.setItem('taskdeck_feature_flags', payload)
+
+        store.restore()
+
+        expect(store.flags).toEqual(defaultFeatureFlags)
+      },
+    )
+
+    it('uses defaults when storage cannot be read', () => {
+      store.setFlag('newAuth', false)
+      const getItem = vi.spyOn(localStorage, 'getItem').mockImplementation(() => {
+        throw new DOMException('Storage blocked', 'SecurityError')
+      })
+
+      try {
+        expect(() => store.restore()).not.toThrow()
+        expect(store.flags).toEqual(defaultFeatureFlags)
+      } finally {
+        getItem.mockRestore()
+      }
+    })
+
+    it('keeps an in-memory flag update when persistence fails', () => {
+      const setItem = vi.spyOn(localStorage, 'setItem').mockImplementation(() => {
+        throw new DOMException('Storage full', 'QuotaExceededError')
+      })
+
+      try {
+        expect(() => store.setFlag('newAuth', false)).not.toThrow()
+        expect(store.isEnabled('newAuth')).toBe(false)
+        expect(store.persistenceError).toBe('Feature flag changes are active for this session but could not be saved in browser storage.')
+      } finally {
+        setItem.mockRestore()
+      }
+    })
+
+    it('clears the persistence error after a later write succeeds', () => {
+      const setItem = vi.spyOn(localStorage, 'setItem').mockImplementationOnce(() => {
+        throw new DOMException('Storage full', 'QuotaExceededError')
+      })
+
+      try {
+        store.setFlag('newAuth', false)
+        expect(store.persistenceError).toBeTruthy()
+      } finally {
+        setItem.mockRestore()
+      }
+
+      store.setFlag('newAuth', true)
+      expect(store.persistenceError).toBeNull()
+    })
+
+    it('does not let stale storage overwrite an unsaved flag update', () => {
+      localStorage.setItem('taskdeck_feature_flags', JSON.stringify({ newAuth: true }))
+      store.restore()
+      const setItem = vi.spyOn(localStorage, 'setItem').mockImplementation(() => {
+        throw new DOMException('Storage full', 'QuotaExceededError')
+      })
+
+      try {
+        store.setFlag('newAuth', false)
+        expect(store.isEnabled('newAuth')).toBe(false)
+
+        store.restore()
+
+        expect(store.isEnabled('newAuth')).toBe(false)
+      } finally {
+        setItem.mockRestore()
+      }
+    })
+
+    it('keeps reset defaults when persistence fails', () => {
+      store.setFlag('newAuth', false)
+      const setItem = vi.spyOn(localStorage, 'setItem').mockImplementation(() => {
+        throw new DOMException('Storage full', 'QuotaExceededError')
+      })
+
+      try {
+        expect(() => store.resetAll()).not.toThrow()
+        expect(store.flags).toEqual(defaultFeatureFlags)
+      } finally {
+        setItem.mockRestore()
+      }
+    })
+
+    it('does not let stale storage overwrite an unsaved reset', () => {
+      localStorage.setItem('taskdeck_feature_flags', JSON.stringify({ devTools: true }))
+      store.restore()
+      const setItem = vi.spyOn(localStorage, 'setItem').mockImplementation(() => {
+        throw new DOMException('Storage full', 'QuotaExceededError')
+      })
+
+      try {
+        store.resetAll()
+        expect(store.isEnabled('devTools')).toBe(defaultFeatureFlags.devTools)
+
+        store.restore()
+
+        expect(store.isEnabled('devTools')).toBe(defaultFeatureFlags.devTools)
+      } finally {
+        setItem.mockRestore()
+      }
+    })
+
     it('should use defaults when no flags are saved in localStorage', () => {
       // localStorage is clear from beforeEach
       store.restore()
diff --git a/frontend/taskdeck-web/src/tests/views/ProfileSettingsView.spec.ts b/frontend/taskdeck-web/src/tests/views/ProfileSettingsView.spec.ts
index f9088bcaa..a10fad609 100644
--- a/frontend/taskdeck-web/src/tests/views/ProfileSettingsView.spec.ts
+++ b/frontend/taskdeck-web/src/tests/views/ProfileSettingsView.spec.ts
@@ -19,6 +19,7 @@ const featureFlagMocks = vi.hoisted(() => ({
   isEnabled: vi.fn(() => false),
   setFlag: vi.fn(),
   resetAll: vi.fn(),
+  persistenceError: null as string | null,
 }))
 
 vi.mock('../../store/sessionStore', () => ({
@@ -38,6 +39,7 @@ vi.mock('../../store/featureFlagStore', () => ({
     isEnabled: featureFlagMocks.isEnabled,
     setFlag: featureFlagMocks.setFlag,
     resetAll: featureFlagMocks.resetAll,
+    persistenceError: featureFlagMocks.persistenceError,
   }),
 }))
 
@@ -115,6 +117,15 @@ describe('ProfileSettingsView', () => {
     expect(wrapper.text()).toContain('Editor')
     expect(wrapper.text()).toContain('Can run editor-safe Ops templates; admin templates are restricted.')
   })
+
+  it('surfaces feature-flag persistence failures', () => {
+    featureFlagMocks.persistenceError = 'Feature flag changes are active for this session but could not be saved in browser storage.'
+
+    const wrapper = mount(ProfileSettingsView)
+
+    expect(wrapper.get('[role="alert"]').text()).toContain('could not be saved')
+    featureFlagMocks.persistenceError = null
+  })
 })
 
 // ── #1808 review (MEDIUM): Legacy ("off") mode substrate guard ──
diff --git a/frontend/taskdeck-web/src/views/ProfileSettingsView.vue b/frontend/taskdeck-web/src/views/ProfileSettingsView.vue
index a7bdfa060..a2a6ef74d 100644
--- a/frontend/taskdeck-web/src/views/ProfileSettingsView.vue
+++ b/frontend/taskdeck-web/src/views/ProfileSettingsView.vue
@@ -329,6 +329,9 @@ const flagLabels: Record<keyof FeatureFlags, string> = {
     <section class="paper-profile__panel">
       <h2 class="tk-h3 paper-profile__panel-title">Feature Flags</h2>
       <p class="paper-profile__panel-desc">Toggle feature flags to enable or disable new features.</p>
+      <p v-if="featureFlags.persistenceError" class="paper-profile__alert paper-profile__alert--error" role="alert">
+        {{ featureFlags.persistenceError }}
+      </p>
       <div class="paper-profile__flags-grid">
         <div v-for="(label, key) in flagLabels" :key="key" class="paper-profile__flag-row">
           <label :for="`flag-${key}`" class="paper-profile__flag-label">{{ label }}</label>