Release Activity in Canary (#34374)

## Overview

This PR ships `<Activity />` to the `react@canary` release channel for
final feedback and prepare for semver stable release.

## What this means

Shipping `<Activity />` to canary means it has gone through extensive
testing in production, we are confident in the stability of the feature,
and we are preparing to release it in a future semver stable version.

Libraries and frameworks following the [Canary
Workflow](https://react.dev/blog/2023/05/03/react-canaries) should begin
implementing and testing the feature.

## Why we follow the Canary Workflow

To prepare for semver stable, libraries should test canary features like
`<Activity>` with `react@canary` to confirm compatibility and prepare
for the next semver release in a myriad of environments and
configurations used throughout the React ecosystem. This provides
libraries with ample time to catch any issues we missed before slamming
them with problems in the wider semver release.

Since these features have already gone through extensive production
testing, and we are confident they are stable, frameworks following the
[Canary Workflow](https://react.dev/blog/2023/05/03/react-canaries) can
also begin adopting canary features like `<Activity />`.

This adoption is similar to how different Browsers implement new
proposed browser features before they are added to the standard. If a
frameworks adopts a canary feature, they are committing to stability for
their users by ensuring any API changes before a semver stable release
are opaque and non-breaking to their users.

Apps not using a framework are also free to adopt canary features like
Activity as long as they follow the [Canary
Workflow](https://react.dev/blog/2023/05/03/react-canaries), but we
generally recommend waiting for a semver stable release unless you have
the capacity to commit to following along with the canary changes and
debugging library compatibility issues.

Waiting for semver stable means you're able to benefit from libraries
testing and confirming support, and use semver as signal for which
version of a library you can use with support of the feature.

## Docs 

Check out the ["React Labs: View Transitions, Activity, and
more"](https://react.dev/blog/2025/04/23/react-labs-view-transitions-activity-and-more#activity)
blog post, and [the new docs for
`<Activity>`](https://react.dev/reference/react/Activity) for more info.

## TODO
- [x] Bump Activity docs to Canary
reactjs/react.dev#7974

---------

Co-authored-by: Sebastian Sebbie Silbermann <[email protected]>

Author: rickhanlonii

fixtures/view-transition/src/components/Page.js

@@ -1,7 +1,7 @@
 import React, {
   unstable_addTransitionType as addTransitionType,
   unstable_ViewTransition as ViewTransition,
-  unstable_Activity as Activity,
+  Activity,
   useLayoutEffect,
   useEffect,
   useState,

packages/react-devtools-shared/src/__tests__/storeComponentFilters-test.js

@@ -199,7 +199,7 @@ describe('Store component filters', () => {
   });
 
   it('should filter Activity', async () => {
-    const Activity = React.unstable_Activity;
+    const Activity = React.Activity || React.unstable_Activity;
 
     if (Activity != null) {
       await actAsync(async () =>

packages/react-dom/src/__tests__/ReactDOMFragmentRefs-test.js

@@ -31,7 +31,7 @@ describe('FragmentRefs', () => {
     jest.resetModules();
     React = require('react');
     Fragment = React.Fragment;
-    Activity = React.unstable_Activity;
+    Activity = React.Activity;
     ReactDOMClient = require('react-dom/client');
     ReactDOM = require('react-dom');
     createPortal = ReactDOM.createPortal;

packages/react-dom/src/__tests__/ReactDOMServerPartialHydration-test.internal.js

@@ -113,7 +113,7 @@ describe('ReactDOMServerPartialHydration', () => {
     act = require('internal-test-utils').act;
     ReactDOMServer = require('react-dom/server');
     Scheduler = require('scheduler');
-    Activity = React.unstable_Activity;
+    Activity = React.Activity;
     Suspense = React.Suspense;
     useSyncExternalStore = React.useSyncExternalStore;
     if (gate(flags => flags.enableSuspenseList)) {

packages/react-dom/src/__tests__/ReactDOMServerPartialHydrationActivity-test.internal.js

@@ -100,7 +100,7 @@ describe('ReactDOMServerPartialHydrationActivity', () => {
     act = require('internal-test-utils').act;
     ReactDOMServer = require('react-dom/server');
     Scheduler = require('scheduler');
-    Activity = React.unstable_Activity;
+    Activity = React.Activity;
     Suspense = React.Suspense;
     useSyncExternalStore = React.useSyncExternalStore;
 

packages/react-dom/src/__tests__/ReactDOMServerSelectiveHydrationActivity-test.internal.js

@@ -139,7 +139,7 @@ describe('ReactDOMServerSelectiveHydrationActivity', () => {
     ReactDOMServer = require('react-dom/server');
     act = require('internal-test-utils').act;
     Scheduler = require('scheduler');
-    Activity = React.unstable_Activity;
+    Activity = React.Activity;
 
     const InternalTestUtils = require('internal-test-utils');
     assertLog = InternalTestUtils.assertLog;

packages/react-reconciler/src/__tests__/Activity-test.js

@@ -24,7 +24,7 @@ describe('Activity', () => {
     Scheduler = require('scheduler');
     act = require('internal-test-utils').act;
     LegacyHidden = React.unstable_LegacyHidden;
-    Activity = React.unstable_Activity;
+    Activity = React.Activity;
     useState = React.useState;
     useInsertionEffect = React.useInsertionEffect;
     useLayoutEffect = React.useLayoutEffect;
@@ -280,7 +280,7 @@ describe('Activity', () => {
 
   // @gate enableActivity
   it('nested offscreen does not call componentWillUnmount when hidden', async () => {
-    // This is a bug that appeared during production test of <unstable_Activity />.
+    // This is a bug that appeared during production test of <Activity />.
     // It is a very specific scenario with nested Offscreens. The inner offscreen
     // goes from visible to hidden in synchronous update.
     class ClassComponent extends React.Component {

packages/react-reconciler/src/__tests__/ActivityLegacySuspense-test.js

@@ -22,7 +22,7 @@ describe('Activity Suspense', () => {
     Scheduler = require('scheduler');
     act = require('internal-test-utils').act;
     LegacyHidden = React.unstable_LegacyHidden;
-    Activity = React.unstable_Activity;
+    Activity = React.Activity;
     Suspense = React.Suspense;
     useState = React.useState;
     useEffect = React.useEffect;

packages/react-reconciler/src/__tests__/ActivityStrictMode-test.js

@@ -10,7 +10,7 @@ describe('Activity StrictMode', () => {
     log = [];
 
     React = require('react');
-    Activity = React.unstable_Activity;
+    Activity = React.Activity;
     ReactNoop = require('react-noop-renderer');
     act = require('internal-test-utils').act;
   });

packages/react-reconciler/src/__tests__/ActivitySuspense-test.js

@@ -23,7 +23,7 @@ describe('Activity Suspense', () => {
     Scheduler = require('scheduler');
     act = require('internal-test-utils').act;
     LegacyHidden = React.unstable_LegacyHidden;
-    Activity = React.unstable_Activity;
+    Activity = React.Activity;
     Suspense = React.Suspense;
     useState = React.useState;
     useEffect = React.useEffect;