feat: add feature usage tracker for nightly surveys (#8175)

Introduces `useFeatureUsageTracker` composable that tracks how many
times a user has used a specific feature, along with first and last
usage timestamps. Data persists to localStorage using `@vueuse/core`'s
`useStorage`. This composable provides the foundation for triggering
surveys after a configurable number of feature uses. Includes
comprehensive unit tests.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8175-feat-add-feature-usage-tracker-for-nightly-surveys-2ee6d73d36508118859ece6fcf17561d)
by [Unito](https://www.unito.io)

src/platform/surveys/useFeatureUsageTracker.test.ts

@@ -0,0 +1,131 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+
+const STORAGE_KEY = 'Comfy.FeatureUsage'
+
+describe('useFeatureUsageTracker', () => {
+  beforeEach(() => {
+    localStorage.clear()
+    vi.resetModules()
+  })
+
+  afterEach(() => {
+    localStorage.clear()
+  })
+
+  it('initializes with zero count for new feature', async () => {
+    const { useFeatureUsageTracker } = await import('./useFeatureUsageTracker')
+    const { useCount } = useFeatureUsageTracker('test-feature')
+
+    expect(useCount.value).toBe(0)
+  })
+
+  it('increments count on trackUsage', async () => {
+    const { useFeatureUsageTracker } = await import('./useFeatureUsageTracker')
+    const { useCount, trackUsage } = useFeatureUsageTracker('test-feature')
+
+    expect(useCount.value).toBe(0)
+
+    trackUsage()
+    expect(useCount.value).toBe(1)
+
+    trackUsage()
+    expect(useCount.value).toBe(2)
+  })
+
+  it('sets firstUsed only on first use', async () => {
+    vi.useFakeTimers()
+    const firstTs = 1000000
+    vi.setSystemTime(firstTs)
+    try {
+      const { useFeatureUsageTracker } =
+        await import('./useFeatureUsageTracker')
+      const { usage, trackUsage } = useFeatureUsageTracker('test-feature')
+
+      trackUsage()
+      expect(usage.value?.firstUsed).toBe(firstTs)
+
+      vi.setSystemTime(firstTs + 5000)
+      trackUsage()
+      expect(usage.value?.firstUsed).toBe(firstTs)
+    } finally {
+      vi.useRealTimers()
+    }
+  })
+
+  it('updates lastUsed on each use', async () => {
+    vi.useFakeTimers()
+    try {
+      const { useFeatureUsageTracker } =
+        await import('./useFeatureUsageTracker')
+      const { usage, trackUsage } = useFeatureUsageTracker('test-feature')
+
+      trackUsage()
+      const firstLastUsed = usage.value?.lastUsed ?? 0
+
+      vi.advanceTimersByTime(10)
+      trackUsage()
+
+      expect(usage.value?.lastUsed).toBeGreaterThan(firstLastUsed)
+    } finally {
+      vi.useRealTimers()
+    }
+  })
+
+  it('reset clears feature data', async () => {
+    const { useFeatureUsageTracker } = await import('./useFeatureUsageTracker')
+    const { useCount, trackUsage, reset } =
+      useFeatureUsageTracker('test-feature')
+
+    trackUsage()
+    trackUsage()
+    expect(useCount.value).toBe(2)
+
+    reset()
+    expect(useCount.value).toBe(0)
+  })
+
+  it('tracks multiple features independently', async () => {
+    const { useFeatureUsageTracker } = await import('./useFeatureUsageTracker')
+    const featureA = useFeatureUsageTracker('feature-a')
+    const featureB = useFeatureUsageTracker('feature-b')
+
+    featureA.trackUsage()
+    featureA.trackUsage()
+    featureB.trackUsage()
+
+    expect(featureA.useCount.value).toBe(2)
+    expect(featureB.useCount.value).toBe(1)
+  })
+
+  it('persists to localStorage', async () => {
+    vi.useFakeTimers()
+    try {
+      const { useFeatureUsageTracker } =
+        await import('./useFeatureUsageTracker')
+      const { trackUsage } = useFeatureUsageTracker('persisted-feature')
+
+      trackUsage()
+      await vi.runAllTimersAsync()
+
+      const stored = JSON.parse(localStorage.getItem(STORAGE_KEY) ?? '{}')
+      expect(stored['persisted-feature']?.useCount).toBe(1)
+    } finally {
+      vi.useRealTimers()
+    }
+  })
+
+  it('loads existing data from localStorage', async () => {
+    localStorage.setItem(
+      STORAGE_KEY,
+      JSON.stringify({
+        'existing-feature': { useCount: 5, firstUsed: 1000, lastUsed: 2000 }
+      })
+    )
+
+    vi.resetModules()
+    const { useFeatureUsageTracker } = await import('./useFeatureUsageTracker')
+    const { useCount } = useFeatureUsageTracker('existing-feature')
+
+    expect(useCount.value).toBe(5)
+  })
+})

src/platform/surveys/useFeatureUsageTracker.ts

@@ -0,0 +1,46 @@
+import { useStorage } from '@vueuse/core'
+import { computed } from 'vue'
+
+interface FeatureUsage {
+  useCount: number
+  firstUsed: number
+  lastUsed: number
+}
+
+type FeatureUsageRecord = Record<string, FeatureUsage>
+
+const STORAGE_KEY = 'Comfy.FeatureUsage'
+
+/**
+ * Tracks feature usage for survey eligibility.
+ * Persists to localStorage.
+ */
+export function useFeatureUsageTracker(featureId: string) {
+  const usageData = useStorage<FeatureUsageRecord>(STORAGE_KEY, {})
+
+  const usage = computed(() => usageData.value[featureId])
+
+  const useCount = computed(() => usage.value?.useCount ?? 0)
+
+  function trackUsage() {
+    const now = Date.now()
+    const existing = usageData.value[featureId]
+
+    usageData.value[featureId] = {
+      useCount: (existing?.useCount ?? 0) + 1,
+      firstUsed: existing?.firstUsed ?? now,
+      lastUsed: now
+    }
+  }
+
+  function reset() {
+    delete usageData.value[featureId]
+  }
+
+  return {
+    usage,
+    useCount,
+    trackUsage,
+    reset
+  }
+}