Fix fullscreen infinite render loop in video embeds (#10807)

eslint-suppressions.json

@@ -650,14 +650,6 @@
       "count": 2
     }
   },
-  "src/components/hooks/useFullscreen.ts": {
-    "@typescript-eslint/no-floating-promises": {
-      "count": 2
-    },
-    "react-hooks/set-state-in-effect": {
-      "count": 1
-    }
-  },
   "src/components/hooks/useLandingEntry.native.ts": {
     "react-hooks/set-state-in-effect": {
       "count": 1

src/components/Post/Embed/VideoEmbed/ActiveVideoWebContext.tsx

@@ -108,10 +108,15 @@ export function useActiveVideoWeb() {
 
   return {
     active: activeViewId === id,
-    setActive: () => {
+    setActive: useCallback(() => {
       setActiveView(id)
-    },
+    }, [setActiveView, id]),
     currentActiveView: activeViewId,
-    sendPosition: (y: number) => sendViewPosition(id, y),
+    sendPosition: useCallback(
+      (y: number) => {
+        sendViewPosition(id, y)
+      },
+      [sendViewPosition, id],
+    ),
   }
 }

src/components/hooks/useFullscreen.ts

@@ -1,10 +1,4 @@
-import {
+import {useCallback, useEffect, useRef, useSyncExternalStore} from 'react'
-  useCallback,
-  useEffect,
-  useRef,
-  useState,
-  useSyncExternalStore,
-} from 'react'
 
 import {IS_WEB, IS_WEB_FIREFOX, IS_WEB_SAFARI} from '#/env'
 
@@ -13,28 +7,38 @@ function fullscreenSubscribe(onChange: () => void) {
   return () => document.removeEventListener('fullscreenchange', onChange)
 }
 
+function getFullscreenSnapshot() {
+  return Boolean(document.fullscreenElement)
+}
+
 export function useFullscreen(ref?: React.RefObject<HTMLElement | null>) {
   if (!IS_WEB) throw new Error("'useFullscreen' is a web-only hook")
-  const isFullscreen = useSyncExternalStore(fullscreenSubscribe, () =>
+  const isFullscreen = useSyncExternalStore(
-    Boolean(document.fullscreenElement),
+    fullscreenSubscribe,
+    getFullscreenSnapshot,
   )
   const scrollYRef = useRef<null | number>(null)
-  const [prevIsFullscreen, setPrevIsFullscreen] = useState(isFullscreen)
+  // Tracked via a ref rather than state so that reacting to a fullscreen change
+  // never schedules its own render. Scheduling a render in response to the
+  // external store value (the old `setPrevIsFullscreen` pattern) was a seed for
+  // the commit-phase update loop reported in APP-315 / APP-5PP / APP-7ZB.
+  const prevIsFullscreenRef = useRef(isFullscreen)
 
   const toggleFullscreen = useCallback(() => {
     if (isFullscreen) {
-      document.exitFullscreen()
+      void document.exitFullscreen()
     } else {
       if (!ref) throw new Error('No ref provided')
       if (!ref.current) return
       scrollYRef.current = window.scrollY
-      ref.current.requestFullscreen()
+      void ref.current.requestFullscreen()
     }
   }, [isFullscreen, ref])
 
   useEffect(() => {
+    const prevIsFullscreen = prevIsFullscreenRef.current
     if (prevIsFullscreen === isFullscreen) return
-    setPrevIsFullscreen(isFullscreen)
+    prevIsFullscreenRef.current = isFullscreen
 
     // Chrome has an issue where it doesn't scroll back to the top after exiting fullscreen
     // Let's play it safe and do it if not FF or Safari, since anything else will probably be chromium
@@ -46,7 +50,7 @@ export function useFullscreen(ref?: React.RefObject<HTMLElement | null>) {
         }
       }, 100)
     }
-  }, [isFullscreen, prevIsFullscreen])
+  }, [isFullscreen])
 
   return [isFullscreen, toggleFullscreen] as const
 }