Agents Manager: externalize react-dom/client to the host's ReactDOM

[iamchughmayank]

Proposed Changes

• Externalize react-dom/client in the Agents Manager widget build so createRoot resolves to WordPress's ReactDOM instead of bundling a copy of react-dom, and map the subpath to the react-dom script handle so it is declared as a dependency.

Why are these changes being made?

The Agents Manager widgets externalize react and react-dom to the React that WordPress provides, but the dependency-extraction plugin does not externalize the react-dom/client subpath — so createRoot pulls a bundled copy of react-dom into the widget. A bundled react-dom ships its own React runtime, which is incompatible with the host's React whenever the versions differ.

Now that calypso builds against React 19 (#112339), a widget rebuilt from trunk bundles react-dom 19 while the block-editor host still runs React 18, which crashes the sidebar at mount (Cannot read properties of undefined (reading 'S') / minified React error 525). Externalizing react-dom/client makes the widget use the host's react-dom, so it always matches the host — React 18 today and React 19 automatically once the host migrates.

Same rationale as odyssey-stats and blaze-dashboard, which externalize the React runtime to the host; this change additionally maps the react-dom/client subpath.

Testing Instructions

1. Sandbox widgets.wp.com and run cd apps/agents-manager && yarn dev --sync.
2. Open the post editor on a Simple or Atomic site and open the AI sidebar — the FAB should render with no React console errors.
3. Confirm the suggestions in the sidebar are working as expected

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• For UI changes, have you tested the affected components in dark mode?
• Have you tested accessibility for your changes?
• Have you used memoizing on expensive computations?
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-187257

Jetpack Cloud Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-187257&env=jetpack

Automattic for Agencies Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-187257&env=a8c-for-agencies

Dashboard Live (dotcom) (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-187257&env=dashboard

Dashboard Live (A4A) (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-187257&env=dashboard-a4a

[Copilot]

Pull request overview

This PR updates the Agents Manager widget webpack build to ensure react-dom/client is treated as a WordPress-provided external, preventing the widget from bundling its own react-dom (and avoiding React runtime/version mismatches with the block editor host).

Changes:

• Externalize react-dom/client to the host’s ReactDOM global so createRoot uses WordPress’s react-dom.
• Map react-dom/client to the react-dom script handle via requestToHandle so the generated *.asset.json declares the correct dependency.

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[github-actions]

Looks like one of the E2E tests has failed.

You can fix them following these steps:

1. Check out this branch locally:

   gh pr checkout 112428

2. Start Claude Code in the repo:

   claude

3. Run the /fix-e2e-tests skill, passing this PR number:

   /fix-e2e-tests 112428
   

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

[wellyshen]

Seems duplicated: #112421

[iamchughmayank]

closing in favour of #112428 (comment)

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.