diff --git a/web/src/hooks/useCodexExplorationCollapse.test.ts b/web/src/hooks/useCodexExplorationCollapse.test.ts
index 70cffe84..de2f3d0b 100644
--- a/web/src/hooks/useCodexExplorationCollapse.test.ts
+++ b/web/src/hooks/useCodexExplorationCollapse.test.ts
@@ -1,9 +1,13 @@
+import { act, renderHook } from '@testing-library/react'
 import { beforeEach, describe, expect, it } from 'vitest'
 import {
     DEFAULT_CODEX_EXPLORATION_COLLAPSED,
     getInitialCodexExplorationCollapsed,
+    useCodexExplorationCollapse,
 } from './useCodexExplorationCollapse'
 
+const STORAGE_KEY = 'hapi-codex-exploration-collapsed'
+
 describe('useCodexExplorationCollapse helpers', () => {
     beforeEach(() => {
         window.localStorage.clear()
@@ -14,10 +18,61 @@ describe('useCodexExplorationCollapse helpers', () => {
     })
 
     it('reads valid stored values and ignores invalid values', () => {
-        window.localStorage.setItem('hapi-codex-exploration-collapsed', 'false')
+        window.localStorage.setItem(STORAGE_KEY, 'false')
         expect(getInitialCodexExplorationCollapsed()).toBe(false)
 
-        window.localStorage.setItem('hapi-codex-exploration-collapsed', 'invalid')
+        window.localStorage.setItem(STORAGE_KEY, 'invalid')
         expect(getInitialCodexExplorationCollapsed()).toBe(DEFAULT_CODEX_EXPLORATION_COLLAPSED)
     })
 })
+
+describe('useCodexExplorationCollapse', () => {
+    beforeEach(() => {
+        window.localStorage.clear()
+    })
+
+    it('persists the expanded preference', () => {
+        const { result } = renderHook(() => useCodexExplorationCollapse())
+
+        act(() => {
+            result.current.setCodexExplorationCollapsed(false)
+        })
+
+        expect(result.current.codexExplorationCollapsed).toBe(false)
+        expect(window.localStorage.getItem(STORAGE_KEY)).toBe('false')
+    })
+
+    it('removes the stored preference when restored to the default', () => {
+        window.localStorage.setItem(STORAGE_KEY, 'false')
+        const { result } = renderHook(() => useCodexExplorationCollapse())
+
+        act(() => {
+            result.current.setCodexExplorationCollapsed(true)
+        })
+
+        expect(result.current.codexExplorationCollapsed).toBe(true)
+        expect(window.localStorage.getItem(STORAGE_KEY)).toBeNull()
+    })
+
+    it('applies cross-tab changes from storage events', () => {
+        const { result } = renderHook(() => useCodexExplorationCollapse())
+
+        act(() => {
+            window.dispatchEvent(new StorageEvent('storage', {
+                key: STORAGE_KEY,
+                newValue: 'false',
+            }))
+        })
+
+        expect(result.current.codexExplorationCollapsed).toBe(false)
+
+        act(() => {
+            window.dispatchEvent(new StorageEvent('storage', {
+                key: STORAGE_KEY,
+                newValue: null,
+            }))
+        })
+
+        expect(result.current.codexExplorationCollapsed).toBe(true)
+    })
+})