fix: count back/forward revisits — key transitions, not key novelty

location.key is stable per history entry, so a POP restores the entry's
original key; the persistent seen-keys set suppressed exactly the
revisits the dedupe intended to count. Track only the current key and
reset the per-page set on every key change: any navigation (push,
replace, pop) counts again, while StrictMode re-mounts and co-located
duplicates within one navigation still dedupe. Memory is now bounded
to the current view instead of growing per session.

Author: paul-phan

packages/hydrogen/__tests__/use-pixel.test.ts

@@ -2,7 +2,7 @@ import { describe, expect, it } from 'vitest'
 import { shouldFirePixel } from '../src/utils/pixel'
 
 describe('shouldFirePixel', () => {
-  it('should_fire_once_per_page_per_navigation_entry', () => {
+  it('should_fire_once_per_page_per_navigation', () => {
     expect(shouldFirePixel('nav-1', 'page-a')).toBe(true)
     // Second co-located instance of the same page (or a StrictMode
     // re-mount) must not double-count the impression.
@@ -12,11 +12,17 @@ describe('shouldFirePixel', () => {
   it('should_count_each_co_located_page_separately', () => {
     expect(shouldFirePixel('nav-2', 'page-layout')).toBe(true)
     expect(shouldFirePixel('nav-2', 'page-child')).toBe(true)
+    expect(shouldFirePixel('nav-2', 'page-child')).toBe(false)
   })
 
-  it('should_count_revisits_with_a_fresh_navigation_key', () => {
-    expect(shouldFirePixel('nav-3', 'page-a')).toBe(true)
-    // Back/forward navigation produces a new location.key — revisits count.
-    expect(shouldFirePixel('nav-4', 'page-a')).toBe(true)
+  it('should_count_back_forward_revisits_that_restore_the_original_key', () => {
+    // location.key is stable per history entry: visiting A, pushing to B,
+    // then pressing Back POPs to A's ORIGINAL key. The key transition (not
+    // key novelty) is what marks a new navigation.
+    expect(shouldFirePixel('key-a', 'page-a')).toBe(true)
+    expect(shouldFirePixel('key-b', 'page-b')).toBe(true)
+    expect(shouldFirePixel('key-a', 'page-a')).toBe(true)
+    // Within the restored entry, duplicates still dedupe.
+    expect(shouldFirePixel('key-a', 'page-a')).toBe(false)
   })
 })

packages/hydrogen/src/utils/pixel.ts

@@ -1,17 +1,27 @@
-// One pixel per page per navigation entry. Nested compositions mount
-// multiple Weaverse instances on one URL (and React StrictMode re-runs
-// mount effects); both would otherwise double-count the same impression.
-// Back/forward navigation gets a fresh `location.key`, so revisits count.
-let firedPixels = new Set<string>()
+// One pixel per page per navigation. Nested compositions mount multiple
+// Weaverse instances on one URL (and React StrictMode re-runs mount
+// effects); both would otherwise double-count the same impression.
+//
+// `location.key` is stable per history entry, so a back/forward POP
+// restores the entry's ORIGINAL key — a persistent "seen keys" set would
+// suppress those revisits. Instead, remember only the current key and
+// reset on every key change: any navigation (push, replace, or pop)
+// transitions the key and counts again, while re-mounts and co-located
+// duplicates within one navigation dedupe.
+let currentNavigationKey: string | null = null
+let firedPageIds = new Set<string>()
 
 export function shouldFirePixel(
   navigationKey: string,
   pageId: string
 ): boolean {
-  let key = `${navigationKey}:${pageId}`
-  if (firedPixels.has(key)) {
+  if (navigationKey !== currentNavigationKey) {
+    currentNavigationKey = navigationKey
+    firedPageIds.clear()
+  }
+  if (firedPageIds.has(pageId)) {
     return false
   }
-  firedPixels.add(key)
+  firedPageIds.add(pageId)
   return true
 }