fix: prevent duplicate items in column selection

app/composables/usePreferencesProvider.ts

@@ -1,4 +1,4 @@
-import { defu } from 'defu'
+import { createDefu } from 'defu'
 
 /**
  * Abstraction for preferences storage
@@ -13,6 +13,13 @@ interface StorageProvider<T> {
   remove: () => void
 }
 
+const defu = createDefu((object, key, value) => {
+  if (Array.isArray(object[key]) && Array.isArray(value)) {
+    object[key] = value
+    return true
+  }
+})
+
 /**
  * Creates a localStorage-based storage provider
  */

test/nuxt/composables/use-preferences-provider.spec.ts

@@ -0,0 +1,63 @@
+import { describe, it, expect, beforeEach } from 'vitest'
+import { defineComponent, onMounted } from 'vue'
+import { mount } from '@vue/test-utils'
+import { usePreferencesProvider } from '../../../app/composables/usePreferencesProvider'
+
+const STORAGE_KEY = 'npmx-list-prefs'
+
+function mountWithSetup(run: () => void) {
+  return mount(
+    defineComponent({
+      name: 'TestHarness',
+      setup() {
+        run()
+        return () => null
+      },
+    }),
+    { attachTo: document.body },
+  )
+}
+
+function setLocalStorage(stored: Record<string, any>) {
+  localStorage.setItem(STORAGE_KEY, JSON.stringify(stored))
+}
+
+describe('usePreferencesProvider', () => {
+  beforeEach(() => {
+    localStorage.clear()
+  })
+
+  it('initializes with default values when storage is empty', () => {
+    mountWithSetup(() => {
+      const defaults = { theme: 'light', cols: ['name', 'version'] }
+      const { data } = usePreferencesProvider(defaults)
+      onMounted(() => {
+        expect(data.value).toEqual(defaults)
+      })
+    })
+  })
+
+  it('loads values from localStorage', () => {
+    mountWithSetup(() => {
+      const defaults = { theme: 'light' }
+      const stored = { theme: 'dark' }
+      setLocalStorage(stored)
+      const { data } = usePreferencesProvider(defaults)
+      onMounted(() => {
+        expect(data.value).toEqual(stored)
+      })
+    })
+  })
+
+  it('handles array merging by replacement (preventing duplicates)', () => {
+    mountWithSetup(() => {
+      const defaults = { cols: ['name', 'version', 'date'] }
+      const stored = { cols: ['name', 'version'] }
+      setLocalStorage(stored)
+      const { data } = usePreferencesProvider(defaults)
+      onMounted(() => {
+        expect(data.value.cols).toEqual(['name', 'version'])
+      })
+    })
+  })
+})